Breeding for Rust Resistance in Daylilies: Part 7

Breeding for Rust Resistance in Daylilies: Part 7

In this installment we will look at techniques of rating rust resistance and susceptibility. I want to stress that this is not a comprehensive coverage of the subject, but is a look at the techniques I use and how those techniques compare to the methods of various other breeders. A comprehensive discussion of techniques and methods of rating rust resistance in daylilies is beyond the scope of a simple blog. This is a complex subject and I hope this small overview can spur further thought and discussion.

Rating Resistance/Susceptibility Levels

This is a complicated issue. The rating of resistance or susceptibility levels is subjective and there is no formal method for evaluation that has been devised which is universal for Hemerocallis. Each person I know doing a resistance selection program has a slightly different rating method, though they are all similar. As well, rust itself can be very variable. In some cultivars, rust is only on the undersides of the leaves. On others, it is on the underside and the upper side of the leaves. This can severally complicate the evaluation process. In time, I would love to see a formal set of working guidelines established for rust sporation evaluation. In the meantime, I will set out here some loose, informal guidelines based on how I and a handful of other breeders who I am in contact with, tend to evaluate for resistance levels.

Before we discuss actual rating scales and systems, I need to stress that the subjective aspect is that people can color their observations with emotion. A great example can be found in various message board posts dealing with rust. Take for instance that one person may have a cultivar, say ‘Joan Senior’, and they post that is it ‘resistant’, then a few posts later another person pops in and posts that “’Joan Senior’ isn’t resistant because it got rust in their garden". The problems here are many. First, while the one person saw no rust, that doesn’t mean it is necessarily “resistant” or “immune”, though it seemed to be in that situation. On the other hand, because the other person saw some rust doesn’t mean that it is ‘not resistant’ either. The later person doesn’t in any way indicate the level of rust seen with such a loose statement, and seems to be equating ‘resistant’ with ‘immune’ as we have discussed earlier when defining these terms.

My experience of the diploid version of ‘Joan Senior’ mirrors that of many other people who are actively selecting for rust and regularly evaluating plants – it shows high resistance, but it isn’t immune. In other words, it can get some rust, and often does in severe outbreak seasons, but it doesn’t get more than about 25-30% coverage in my experience and I haven't seen rust on the upper sides of its leaves. To me, that then is a resistant cultivar, but if I was deluded into thinking that any rust at all meant “no resistance” and I thought they had to have no rust to be “resistant”, I might have an emotional reaction and make a broad, subjective statement like, “It got rust here. It is not resistant.” Real resistance is a more nuanced thing than generalizations allow. Further, the misconception that the only resistant plants are those that never show rust creates an artificial expectation that is harmful to any actual realistic effort toward evaluating resistance levels and can likely lead to an emotional reaction that might color one’s ability to rate the subject.

The most important tool you can take into the garden with you during an active spore outbreak is detachment. More than anything else, detachment will help you to remain calm and not give in to emotionalism, which is very counterproductive to accurate observation. Scientists value detachment, and a few actually achieve it: those who do make great researchers. Likewise, those who can achieve some detachment when evaluating their own plants for rust will be able to achieve a more accurate and consistent rating that is closer to the reality of what the plants are actually displaying.

In my own rating style, I prefer to use a general 4 level range, which I label ‘A’ through ‘D’. I also allow for half steps (yes, I have studied music also) that are represented by a + or – symbol. The highest rating in my system is ‘A+’, which we could also call ‘apparently immune’ (I use ‘apparently’ to not imply false certainty). In this way I can actually chart about ten possibilities within the overall arc of the four main rating levels.

I know several people who use a numerical rating of 1 through 5 and a couple who use a rating of 1 through 10. Others use titles and their abbreviations such as ‘Rust resistant’ (RR) for the highest level through ‘Poor Resistance’ (PR) for the lowest with other nomenclature in-between. Others simply use phrases such as ‘excellent resistance’, ‘average resistance’, 'good resistance’, etc. The rating system at All Things Plants database uses a numerical scale of 1 through 5, but they each have many shadings between, such as 2.5, 1.3 or 3.8, etc. The university research studies I have seen tend toward a simple numerical rating system. All of these systems work and each are basically saying the same thing. Through observation and comparison, I can use most anyone’s scale and translate it to mine. Some are more detailed than mine, some less. I find a looser scale more effective, as it is very difficult to be very specific, especially in systems that are using the evaluations of many people with different situations and different ideas about what each level is.

I will now set out the parameters of my system and then you can use that as is or you can adapt it in any way you like. The best possible thing to do is to talk to many people, compare their systems and create a hybrid system that allows you to interface with many systems. That is what I did. I will also attempt to make some comparisons of other systems with mine so you can have an idea of how it interfaces with other’s nomenclature when you run across it.

The system I use is based on the first four letters of the alphabet – A, B, C, and D. In general terms, A is high resistance or low susceptibility, B is good resistance or moderate susceptibility, C is low resistance or high susceptibility and D is very low to no resistance or very high to total susceptibility. Immunity is something higher than any level of resistance, and is rated as A+. Any rust spores at all knock the A+ allegedly immune plant down to an A rated plant. An A plant is still exceptional, highly desirable and very usable in breeding. They may in fact be the most useful plants for breeding in many ways.

Now, let’s look at the numerical percentages I equate with each letter. A+ is no rust spores or 0% spore coverage on either side of any leaves on the plant, while A is 1% to 25% spore coverage on the underside of any number of leaves on the plant. B is 25% to 50% rust spore coverage on the underside of any number of leaves on the plant, while C is 50% to 75% spore coverage on the undersides of the leaves on the plant. D is 75% to 100% coverage of the underside of the leaves by rust spores.

To complicate things, rust can also appear on the upper side of the leaves of some cultivars while never appearing on the upper sides of leaves of other cultivars, regardless of how resistant or susceptible they are. To me, this seems to either be higher susceptibility or a further genetic factor that allows spore formation on the upper sides of the leaves. In either case, I don’t like it and when this occurs, that knocks the rating of the plant down by a half notch to a full notch, depending on how severe the spore coverage is on the upper side of the leaves.

For instance, if a plant shows 20% coverage on the underside of, let’s say, half its leaves, it is an A rated plant, but if that same plant also shows ten percent coverage on the upper sides of the leaves, then it becomes an A-. Further, if the same plant shows coverage as heavy or heavier (almost unseen in my experience) on the upper side of the leaves as on the underside of its leaves, it is then knocked down a full ranking to a B. Since I am not literally counting every spore and measuring the square millimeters of coverage versus uncovered areas of the leaf, this is subjective.  The key is to practice, spend a lot of time looking at infected leaves from various cultivars and compare infected leaves from various cultivars to each other to gain as impartial and subjective an eye as you can. Some people are going to be better at this than others, but I do not rule out the ability of the hobbyist to do this. After all, hobbyists often learn to observe a great deal of minutia such as petal width, teeth and edge details, shading of colors, etc. Either acting as if you can’t do it or getting emotional over rust being on a cultivar you have a given attachment to (positive or negative) will derail the process faster than anything else can and lead to (sometimes wildly) inaccurate perceptions.

I can’t stress enough how important it is in all aspects of rust to just take a deep breath and realize that the world won’t end over it. In most instances, taking a step back and realizing that the problem is manageable and that you aren’t about to be ‘wiped out’, ‘utterly ruined’ or ‘totally annihilated’ is a good first step. Then, rather than running at break-neck speed for the sprays or starting to rip things with a speck of rust out of your garden willy-nilly, you can calmly proceed to begin making observations, some careful notes and over the course of a few weeks, begin to get a feel for what cultivars are more or less effected and formulate a sensible plan from which to proceed. In that calmer mindset, you can then make the critical evaluations with an eye less colored by emotion or sensationalism.

Learning to properly evaluate the level of rust on any given cultivar is not easy, but it is also not extraordinarily difficult. It is not impossible! It can be done and I have faith that you can do it. There are some simple points to consider that will help. In some instances, the rust actually manifests in ways that can help you determine what you are seeing. It is not uncommon to see rust on fairly resistant cultivars clustered only on the tips of the undersides of the leaves, or in some instances, at the bases of the leaves. In those instances, you can fairly easily gauge how much of the underside of the leaf is covered just by measuring how long the leaf is, and then how much of the leaf is covered in rust, or you can then prepare an average from several leaves on that cultivar for even more accuracy overall. A little math is required, but it isn’t a quantum formula.

In other instances, the rust may be scattered over the entire surface of the underside of the leaves or on both sides of the leaves, much like a scattering of salt. The amount can vary widely. The easiest way to come to a conclusion of coverage in this instance is to attempt to judge how much leaf is showing through the salting of spores. This is more difficult to gauge than when the rust is restricted to a specific portion of the leaf, but it is not impossible to gauge. I hope in the future that we can come up with a series of photos showing leaves with different levels of rust to create a general visual guideline for those new to evaluating rust levels, but until that gets done, I hope these general ideas can help you to make some fairly accurate evaluation assessments in your own garden.

In comparing my system of A-B-C-D to other systems, I have found that the numeric system of 1-5 equated quite closely, with 1 = A+, 2 = A, 3 = B, 4 = C, 5 = D, generally speaking. If decimal points are used, then the various decimal points indicate shadings between the main letter/number scores, much as I use a plus or minus. When 1-10 is used, it seems that 1 = roughly A+, 2-4 is about A, 4-6 is about B, 6-8 is about C and 8-10 is about D, approximately. For those systems that use descriptions of resistance I find that Rust Resistant (RR) = A+, Highly Resistant (HR)= A-B+, Moderate Resistance = B-C and Poor Resistance (PR) = C- to D. In other description systems Excellent Rust Resistance seems to be similar to the upper end of my A range, Very Good Rust Resistance is in the A-B range, Good Rust Resistance seems to be about my B level, Average Rust Resistance is about C and Poor Rust Resistance is about the D level in my rating system.

Before we finish this section, we must consider some other eccentricities of rust that will have a bearing on evaluating resistance levels of various cultivars.

First, rust infestation can progress throughout the season, so what may look like an ‘A’ rating in August could well be a ‘C’ or ‘D’ rating by the end of October. It is thus important to start weekly or twice monthly evaluations from the first appearance of rust up through the first killing frost (in climates with enough cold to get killing frosts) when rust sporation will end for that season. There can be tremendous variation in the actual final resistance/susceptibility level and that which the subject starts out with. Some very susceptible cultivars will have heavy spore coverage from the first appearance of rust. Others only gradual increase to heavy spore levels. If I had to choose a plant that shows heavy spore coverage for breeding, I would prefer to use the individual that has slower progression of coverage to heavy levels.

Those that spore heavily almost as soon as rust appears may be the least suitable selection for breeding, as they show the most susceptibility and due to the heavy sporation from the beginning of spore appearance, these cultivars often exhibit a strong impact on vigor and subsequent performance, showing low tolerance to rust, while those that gradually move from light spore coverage to heavy spore coverage over a few months seem to have less impact on their vigor and performance due to the rust infection and would be examples of higher tolerance to rust. In the most tropical regions of the country, these susceptible plants with low tolerance to rust can even dwindle and die from the long-term impact of rust infestation. It is very important to regularly evaluate the levels of rust throughout your rust cycle, but it is also important, where highly susceptible cultivars are not culled out of the garden (as in a breeding program for resistance where some rusty individuals are required to inoculate the seedlings each year) to evaluate their performance the next season to see if their vigor and performance is heavily impacted by the heavy rust infestation of the previous year.

Another point that we often hear is that some will say, well, this or that cultivar was highly resistant or immune last year, but this year it is showing a lot more rust. I suspect that a given cultivar does not build up or loose its genetic resistance to the same strain of rust over time. I suspect in such instances there is either environmental difference between the years that have impacted the plant(s) in question, or you are seeing variable resistance from one year to the next because of the presence of different strains of rust in those years. Certainly, those who regularly spray cannot make a qualified statement on resistance levels at all, nor make observations about the levels of resistance in a given cultivar or clone from year to year. As the years wear on and we keep moving plants around throughout the country, we will see more and more strains of rust in our areas. Hopefully there will be some labs that will offer testing for strain identification in the future.

One final point I want to touch on is that any garden can have variable environmental factors, while different gardens will likely represent environmental differences as will different regions around the continent. Environment can influence the expression of resistance. One report from one year from one garden is highly unreliable. Multiple reports representing many gardens gives a much better chance of understanding actual resistance. When multiple years are also factored in from multiple gardens, that gives a much better picture of actual resistance. With that said though, even one garden can make for better evaluation by using multiple clumps of the same cultivar or seedling scattered throughout the garden. Both multiple clumps and random arrangement, even within one garden, gives a much better insight into the actual resistance of a given plant and helps to neutralize environmental effects. This is but one technique to help eliminate environmental effects and come to a better evaluation of actual resistance. There are also other techniques used by professional researchers to formulate statistical models that can help to eliminate environmental effects.

The evaluation of rust has not yet been standardized, and that is a shame, but we must move forward anyhow, learning to evaluate rust on our own, if necessary. Trust me, after a few seasons of closely observing rust outbreaks and spore coverage, you will develop a keen eye for the various manifestations of spore levels and you will begin to know the range of acceptable sporation (resistance/susceptibility) that you can live with and want to aim for in your own breeding work. Keeping some sort of record system is also very helpful, in order to compare resistance levels from one year to the next in order to gain an overall impression of resistance in any given cultivar and to perhaps also gain some insight into those years when anomalous results may indicate the presence of an alternate strain of rust. In closing I can’t stress how important it is to not freak-out the first time you get an outbreak and to proceed cautiously and carefully, observing with the most detached stance you can achieve. Make observations and evaluate your plants, It doesn’t matter if you did the evaluation ‘right’, just that you are making the attempt and at least learning the variations of resistance/susceptibility and tolerance in your own garden. That is the first step and all else follows from there. 

In the next installment we will look at many points that don't conveniently fall into one particular subject heading...

Merry Christmas!

Breeding For Rust Resistance in Daylilies: Part 6

Breeding For Rust Resistance in Daylilies: Part 6

This post is arriving a little faster than the others in the series have because it is a continuation of the last post, so I wanted to get it up while the last post was still fresh in our minds and before we move into the holiday week. Let's just dive right in...

Practical Techniques For Resistance Breeding: Part 2

To refresh our memories before we proceed, the five systems of mating as outlined by Sewell Wright are listed below. For a more definition of each, please refer to the previous post in this series.

1)   Random Mating {RM}

2)   Genetic Assortative Mating {GAM}

3)   Phenotypic Assortative Mating {PAM}

4)   Genetic Disassortative Mating {GDM}

5)   Phenotypic Disassortative Mating {PDM

The first of these five systems, Random Mating (RM), can be of use in breeding for rust resistance if the entire population shows some level of resistance on the higher end of a bell curve (i.e., moderate to high resistance or immunity). In this system, allowing open pollination (OP) is one way to go, or one could simply mix any number of pollens from various donors (or all of the plants in the population) to apply to as many of the plants in the population as desired. Either way allows for random mating. Yet, with this system, while resistant individuals will likely be created and perhaps even plants desirable on other levels, there is much less control over the direction that the population moves in. With that said, even this system, if only highly resistant individuals are selected each generation, can generate increases in resistance and the creation of highly resistant plants.

Of these five systems of mating, the most effective for breeding for rust resistance is 2 and 3 – Genetic Assortative Mating (GAM) and Phenotypic Assortative Mating (PAM). In both of these methods, two plants showing rust resistance are being mated. In GAM, two related, rust resistant plants are mated, while in PAM two unrelated rust resistant plants are mated. The first then is inbreeding using ‘like x like’, while the second is outcrossing using ‘like x like’. Both can be very effective for concentrating rust resistance. As it is highly likely that we have multiple genes for rust resistance, #3 (PAM) has the added possibility of combining multiple genes for resistance, while #2 (GAM) will concentrate the genes already present in that family line. We can see then that both of these mating systems are very important for breeding rust resistance, and both then are foundational to that work. However, the 4^th and 5^th systems also have uses.

In regards to breeding for rust resistance, the 4^th (GDM) and 5^th (PDM) systems would generally involve crossing a highly resistant or immune individual to a moderate or low resistance individual though not exclusively. The 5^th (PDM) could involve a wide cross for phenotypic reasons (flower, plant habit, foliage type, etc) that use two rust resistant plants or the 4^th (GDM) could involve a cross of two resistant plants that have been shown to have very different genetic types of resistance. Both GDM and PDM can be used to blend multiple types of resistance to create a broader-based resistance genotype/phenotype. Where GDM focus more on different genetic types of rust resistance (genotype), PDM focuses more on different phenotypic expressions of rust resistance (i.e., a seemingly immune plant crossed to a plant showing consistent partial resistance or where each parent shows resistance to a different strain of rust). When either GDM or PDM are used to cross a resistant x non-resistant plant, this is generally what I refer to as a ‘salvage project’.

Now, let us look at these points in more practical terms. In resistance breeding, the most common and effective strategies involve breeding two resistant individuals. This is the fastest path to getting more resistant offspring. Of course, when dealing with more than one gene for resistance, we are not always assured of resistant offspring in the first generation (F1), especially if we mate two resistant plants carrying recessive resistance genes and those genes are not compatible (i.e., at different alleles - this however in practice seems to be very rare). However, when that F1 were intermated to create the second generation (F2), not only would each type of resistance reoccur in some of the offspring, but a small number should express both types of resistance in one plant, but I don’t want to get sidetracked because in most instances, two resistant plants throw some resistant offspring. 

As mentioned above, if two related resistant plants are crossed (GAM), then you are concentrating the genes for resistance within that family. You may get a few offspring with greater resistance than either parent in this way, many with the same levels of resistance as the two parents and some with less resistance than either parent. This is a very effective tool when a family line showing high resistance has been identified, as it will allow you to concentrate the best they have to offer, perhaps creating individuals with much greater resistance than the line began with. This is also why it is so important to identify specific resistant plants as well as family lines that show clearly heritable resistance – these plants need to be used both for outcrossing and then for subsequent inbreeding (GAM) to concentrate and explore their resistance factors.

If two unrelated resistant plants are crossed (PAM), you may be dealing with the same type of gene(s) or you may be combining different types of genes. If one of those genes is dominant from either parent, then you can expect (in theory) as many as 50% (somewhat) resistant offspring from such a mating if the parent with the dominant gene is heterozygous for the gene and as many as (in theory) 100% showing some resistance (not immunity!!) if the parent with the dominant gene is homozygous for the gene, though in practice we rarely see such high numbers, or at least do not recognize them as the resistance levels of heterozygotes can be variable. If both plants are carrying multiple genes, then the outcomes can be very variable (this might be termed ‘quantitative expression’), but as long as some of the recessives are compatible genes, you should see some resistant offspring. It is likely you will see a few offspring as or more resistant than the parents, but not always (as mentioned above, you could even get none, though this would be unusual). However, in general practice, this method seems to work well to produce resistant offspring and often to increase the resistance of a few of them as well. Further, this method can be used to combine multiple genes for rust resistance in an effort to both increase resistance and create lines with a broader base of resistance that may offer resistance to more than one strain of rust. This will be an important challenge in time.

When we want to do a ‘salvage project’ (a specific example of GDM or PDM) we will generally be looking to cross a more resistant plant to a less resistant plant, and often a very susceptible plant, at that.  In doing this type of work, the best results are had when a highly resistant (or immune) plant is one of the parents, especially if the second parent is very susceptible. While even then we might not expect the offspring to be highly resistant, we may see some increase in resistance in the offspring, but even if we don’t we still have added some recessive genes for resistance to the offspring, so we should select through them, noting their resistance levels and where possible, choosing those with the highest levels and then mating those offspring to another resistant plant (usually the best route to increase the resistance in the next generation by brining out some homozygosity for the hidden recessives) or mating them together and watching for the most resistant offspring (which again, would indicate individuals with a concentration of the desired genes).

A salvage project may not be an overnight success. They take patience and one may have to go through two or more generations to start seeing the flower phenotype we want to save from the ‘salvage plant’ recombined with the resistance factors from the resistant plant. If we are careful and patient, taking our time to research resistant plants, and choose something that is resistant that is a good match for the ‘salvage phenotype’, then we can more quickly get back to that phenotype. Say, for instance, that we have a patterned seedlings or cultivar that shows exceptional pattern, but is very rusty. We want to utilize the genes for great pattern, but increase rust resistance. So we research know resistant cultivars to find something that is both highly resistant and shows pattern and we use that in our cross to the salvage plant. In this way we are both introducing rust resistance and making every effort to retain and increase the pattern genetics. Can you see then how this is really not that different from what you already do? Let’s change the word ‘rust’ to ‘bud count’ and see if the example is still so scary.

You have an excellent patterned cultivar with poor bud count. You want to increase the bud count while retaining the fine pattern. You research cultivars with high bud count and locate one that shows high bud count and is also patterned. You cross the two and work with the progeny to retain the fine patterning of the low bud count individual while recombining that trait with the high bud count of the outcross plant. This is the exact same thing I am describing, and you are probably all already doing projects just like that, so don’t get freaked out by this being about rust. Can you see how rust resistance can become just another trait you select for, just like any other? You already do salvage projects, but you do them for things like bud count, branching, flower opening, spotting, etc. Any flaw that keeps you from introducing a plant with otherwise good traits, but the plant has other traits that are so good you keep it as a breeder and breed from it, striving to increase its good traits and ‘iron out’ the flaw, is the exact equivalent to a wonderful plant with rust susceptibility.

The most important thing to remember about any salvage project, whether it is for rust susceptibility or low bud count, is that you may need to raise a large number of seedlings in order to get away from the flaw and replace it with its desirable opposite, and you may not be able to do it in one generation. So any salvage project may represent an investment of more time and space than other projects. In regards to rust resistance, you may get few resistant offspring and take longer to get resistant offspring than if you don’t pursue a salvage project at all. Always weigh the challenges of a salvage project to see if it is really worth pursuing. It may or may not be and that will entirely depend on you.

I now want to touch on a few final points in breeding schemes. There are three very basic mating strategies that can be very helpful. This first is to simply cross two individuals (called a hybrid single cross). We then call these plant ‘A’ (the pod parent) and plant ‘B’ (the pollen parent). Their offspring are ‘AB”. The ‘AB’ offspring can then be selfed, mated to other ‘AB’ siblings, backcrossed to either parent or outcrossed to an alternate plant/line.

The second is when plant ‘AB’ is outcrossed to a third plant (plant ‘C’), we get a three-way cross (AB X C or C x AB). The registry is full of plants reflecting this type of breeding and it is very common in daylily breeding. It also may utilize PAM where plant ‘C’ is unrelated to “AB’ (outcross) or GAM where plant ‘C’ is related to plant ‘AB’ (inbreeding). Any of these techniques are excellent for enhancing and concentrating rust resistance and are also useful in salvage projects, as well.

The third is when two the offspring of two hybrid single crosses are mated and is called a double cross. In this instance, you might notate it as Plant ‘AB’ and plant “CD”. Either plant can be pod or pollen parent, provided they are fertile that direction. This type of mating combines a greater diversity of genes, especially if none of the main plants (plant A, B, C or D) are closely related. If the phenotypes that we are seeking to combine are not genetically compatible (the same genes), we may not see much expression of the target trait in the F1 from crossing ‘AB’ and ‘CD’, but then that F1 can be selfed or intermated to bring out the target traits. The double mating scheme is a great way to combine multiple genes for rust into a later generation, bringing up to four different packages, eventually, into one group of offspring, with some few perhaps expressing homozygosity for all the genes involved. Where all four initial plants have the same genes for resistance, or are equally expressing those genes (i.e., all highly resistant), this method (as with the other two) can be a way to combine flower traits while also combining rust resistance. So you see, there are ways to select for rust resistance and the all-important ‘face’ at the same time!

Another point I want to discuss in regards to breeding strategies is recurrent selection, which is where one identifies the most resistant individuals and uses them to produce the next generation. This is the essence of resistance breeding. This strategy is used to increase and concentrate the targeted trait(s) within a population. The ‘keepers’ are selected repeatedly based on the highest levels of resistance and bred together to increase the amount of resistance. You do the same thing when selecting for any other trait, such as teeth or patterns or edges, thinness or roundness of petals, etc, when you keep the biggest teeth, edges or most strongly patterned, the thinnest or roundest petaled and keep breeding those together every generation. We know from those examples what we can achieve. We can increase resistance to diseases, rust and others, in just exactly the same way we have with other phenotype traits. It is most strongly through recurrent selection that we can do this.

Finally, one last technique I want to mention is the use of a recurrent parent. The recurrent parent is a more focused or narrow form of recurrent selection and is basically a backcross method of using recurrent selection. I have referred to this in the past as making good use of an exceptional individual and have made great strides with this technique in resistance breeding in poultry. The exceptional individual is very rare. They encompass many good traits and score highly for all those traits. In addition, they also have high breeding value, which means they can pass their good traits on in reasonable to high numbers to their progeny. Not all exceptional seeming individuals will have high breeding value, so when you find that combined with many good traits, you have found a real jewel worth its weight in gold!

In using the exceptional individual (recurrent parent) with high breeding value in recurrent selection, we cross it to another plant (called the donor parent) to make F1 offspring and then we backcross those offspring to the exceptional individual, to make a BC1. If this inbreeding does not reveal hidden deleterious traits and we see no indications of inbreeding depression, we may then continue to take the most resistant offspring from each BC over the recurrent parent for several generations. In doing this, we must watch carefully for signs of deleterious traits appearing or for inbreeding depression, but should none appear, backcrossing to the exceptional individual can concentrate and strengthen the exceptional traits and breeding value of the line, creating a line that is highly homozygous for good traits and that can then be used in many other directions with confidence of imparting a highly concentrated package of genes to those offspring. For instance, highly resistant plants from such a backcrossing scheme, as well as the recurrent parent, would make excellent subjects to use in salvage projects for crossing to the ‘salvage plant’.

In closing this section, I would mention that these are just a few of the possible breeding schemes that can be pursued. For a greater discussion of schemes, see the bibliography I will present at the end of this series. I do want to stress that there is not just one strain of rust, so in time, some of the more complex schemes and techniques I have described here will be necessary to begin combining lines of resistance to create plants with multiple forms of genetic resistance, offering a broad based resistance to multiple strains of rust. However, until we know more about the various strains of rust and can gather data on which cultivars show resistance to which strain of rust, we should approach this breeding in simpler ways, dealing with the rust that we encounter in our own gardens and working from there, allowing that a cultivar that was resistant one or more years, but suddenly shows significantly lower resistant in a subsequent year may have encountered a new strain of rust for the first time and to which is has lesser resistance. This will happen and we shouldn’t freak out when it does. It is highly likely that the plant still has resistance to one or more strains of rust and didn’t ‘fail’. The answer would then be to outcross that cultivar to another cultivar that did show resistance to the strain of rust encountered in that year, and in that way begin to blend the two packages of resistance genes.

It is important to realize at the start that there will never be a time when rust resistance breeding it ‘done’. That is highly unrealistic. What we should be striving for instead is to remain calm and remember that our goal is to stay one step ahead, not to somehow defeat the evolution of this pathogen forever, which is something we likely can’t do. Our goal is to improve the situation and reduce the number of highly rusty plants that enter into registration and the gardening world.

In the next installment, we will look at evaluating and rating rust resistance levels as well as various rating systems that are commonly in use.

Breeding for Rust Resistance in Daylilies: Part 5

Breeding for Rust Resistance in Daylilies: Part 5

In this installment, we begin to look at breeding programs and breeding techniques. As this section is rather long, I have divided it into two parts. In this section we will look at concepts of breeding and in the next section we will discuss these concepts as they apply to breeding for rust resistance.

Practical Techniques For Resistance Breeding: Part 1

There are many ways one can go about incorporating resistance to rust (or crown rot, spring sickness, etc.) into his or her breeding strategies. Those who have the best opportunity to do so will be people breeding in the deep south, where rust is a year round issue (or wherever a given pathogen/problem is most active), but people in other locations can make a contribution in their own way as well. All-out resistance breeding such as one might expect from a USDA agricultural station is probably impractical for any hobbyist (and yes, even the ‘big names’ are hobbyists when compared to true commercial agricultural endeavors, be they for ornamentals or food). However, that doesn’t mean that hobbyists can’t make great strides in intensifying the levels of resistance seen in their breeding programs.

One of the first steps is to begin to identify cultivars that show some level of resistance. The next step is to allow rust to run through your seedlings when it appears in your garden, even if only in the fall once every few years. This is certainly better than doing nothing. Interested persons in the south, especially if they are not actively selling plants, can discontinue spraying programs and test their daylilies against rust throughout the year. They have the greatest opportunity to make fast strides in breeding for resistance and in both identifying resistant and susceptible cultivars and putting that information to use in their programs. As well they could be of great benefit to others by sharing that information so those who do not have their ideal testing situation can benefit from their experience. For those who may be collectors in the deep south, not selling or hybridizing, and who would be willing to host plants from northern breeders and not spray (at least in the fall and preferably year round) a great service would be to gather data on resistance levels of those hosted plants and relay it back to the breeders. Those willing to do so could be trained in observation of rust and rating rust infection so that accurate ratings could be assessed. Anyone willing or able to do this would be providing a highly useful and specialized service for his or her fellow hemerocalliphiles!

It is important to understand that there is a difference between immunity, resistance and tolerance. I can’t stress this enough, so I will repeat here the differences. Immunity is when an organism shows no susceptibility to a given pathogen. Resistance is when the organism shows some susceptibility to a pathogen, but the effects are not as severe as in the worst individuals. The level of resistance can vary widely between individual clones. Tolerance is the ability of a given organism to show lower-than-average adverse effects from the presence of a given pathogen.  And of course we should also consider susceptibility, which means showing effects from a given pathogen. Susceptibility will vary from mild (also called ‘high resistance’) to highly susceptible (‘low resistance’, which is sometimes lovingly called “a rust magnet” as these highly susceptible individuals often seem capable of literally sucking rust out of the air).

In selecting potential breeding stock for a resistance breeding project, one mistake that many people make when beginning to resistance breed any species, is that they believe they have to start with totally immune individuals, but that is not the case. I suspect there is one or more major genes that show dominant gene action and infer near or total immunity to rust, at least when homozygous. I suspect this would not be terribly common in daylilies, but it is likely to exist. However, I suspect that the majority of resistance we see is the accumulation of lesser factors (minor genes or polygenes) that accrue to increase resistance incrementally. Many of these factors seem to be recessive, so it is possible that even some very rust susceptible plants are carrying genes for resistance (and only test matings to other resistant plants would confirm or deny this, and I mention it because it is possible to get a resistant offspring from a susceptible parent, and even when both parents are susceptible, there is still the slight possibility of an offspring with some level of resistance higher than the parents, suggesting both may be carrying recessives for resistance).

So let us first consider the different types of breeding programs we might adopt in regards to rust. I see three major ways this could be approached: 
1) – Breeding for resistance as a major focus with all efforts geared toward producing the highest levels of resistance in the most offspring, i.e., making every effort and using all resources at one’s disposal to move the levels of resistance within the entire gene pool maintained towards high resistance and/or immunity. 
2) – Breeding for resistance as a major trait to be selected for, but not as the sole focus of the breeding program, i.e., seeking to increase the levels of resistance in one’s overall gene pool, but not making resistance the sole point of focus. 
3) – Passive selection that would encompass an awareness of rust and rust resistant cultivars, incorporating one or more of those resistant cultivars into the breeding program and noting, recording data about and possibly culling (especially seedlings) for rust on the occasions when rust does appear in the garden, i.e., seeking to at least incorporate some resistance genetics into the overall gene pool and being somewhat educated about rust in general. 

I would stress that none of these three groups necessarily have to be mutually exclusive, nor do they all have to be pursued in the exact same way. Each breeder must decide where on the spectrum he or she wishes to fall and then proceed from there.

Now let us consider each of these three categories for a moment. The first may be pursued by a university or professional operation and with many thousands of seedlings, strict controls and protocols and extreme notation, and might also incorporate lab techniques and methodology. This is likely outside the realm of possibility for any hobby breeder. However, any hobbyist may chose to emulate some of those protocols and make resistance the main focus of their breeding. This would be the strictest and most focused system and likely produce the fastest results. I also have to say that I think it is the least likely to be pursued by hobbyists. This style of breeding may well be too narrow in focus for most hobbyists, but if you think you are cut out for it, then please, only allow me to encourage you. I am not cut out for that system, as I have too many interests beyond simply creating resistant lines, and after having spent many years doing this type of work with poultry, I simply want my daylily work to be a bit more creative and fun; a touch more light-hearted while still taking rust resistance and other plant performance traits seriously. I think most reading this will feel the same way.

The second category is much more realistic for hobby breeders, even those who want to make breeding for resistance a major factor (but not the sole factor) of their work. This system is probably more suitable to hobbyists because it allows focus on other points beyond resistance and can be pursued a bit more casually (even though you may still be very serious about what you are doing). I know breeders out there who have been pursuing such a program for some years with great success. This type of program is probably most suitable for those in the Deep South or anywhere that rust is recurrent yearly and preferably in both spring and fall, but could still be utilized by those only with fall rust or who may not see rust every year, though it will be a bit harder there and may require special considerations. This is more in line with the system I am pursuing in my own breeding work.

The third category is for everybody else. It will be useful for the greatest number of breeders and is much more passive in nature. This style will be especially important for breeders in the North and for those who do not recurrently and reliably get rust (even in the fall), those who must spray (at least in the spring and summer) because they sell and those who want to help in some way but don’t have the time, energy, interest, expertise or proper setting/location to pursue a more elaborate program. This system would be based around incorporating known resistant plants, cultivars or seedlings, and utilizing those in the breeding program. This could encompass as many or as few resistant cultivars as desired. If one wanted to be as active as possible in the passive program, one could make an effort to collect allegedly resistant plants, putting emphasis, for instance, on those that have been resistant in many locations and over many years. Conversely, one may take their time, research and speak to many individuals and find only a handful of know-resistant cultivars that suit their other interests and incorporate those into the program.

The key is to bring in plants that show resistance and use those in the breeding program. In this way, there is at least the chance of increasing the level of resistance factors in one’s gene pool. There would be special considerations with this work that is discussed further below and it must be realized that this type of system will not actively create resistant plants or lines, but will increase the chances of such. One other thing that can greatly enhance this is to allow rust to manifest on the occasions when it occurs, especially in the seedlings and if possible, to send select seedlings to more reliably rusty locations for further testing. At the very least, gathering anecdotal evidence from client sources can help you to make selection decisions and that information could be offered, merely for what it is – anecdotal – to your clientele and other breeders. If neither of these is possible, at the very least, you are considering rust, you are educating yourself about plants with resistance and you are making some effort to include plants with resistance for the chance of increasing resistance in your program. That beats doing nothing, or inadvertently breeding from a group of highly susceptible plants!

With any system you chose to work within, there is a group of well-known breeding methods that can be employed. I will list some that are well-known in the plant breeding profession and then we will discuss them in less technical and more hobby friendly terms in the second part of this topic.

In 1921, the well-known American geneticist Sewell Wright described five types of plant mating that can be applied to plants that are self-fertile or can be outcrossed. These five mating systems are fundamental to all plant breeding, though some are used more than others, depending on the type of plant breeding being pursued. At some time or another, all of these five have been used for breeding daylilies, and all have their practical applications still. These five systems are as follows: {Note – the abbreviations are my own notation system for convenience}

1. Random Mating {RM} – This is open pollination, generally speaking, where any plant in flower at the same time has an equal chance of being crossed with any other in flower at the same time.
2. Genetic Assortative Mating {GAM} – This is hybridizing with plants of related background and is used for line breeding to fix the favorable traits (genes) and works toward homozygosity of those traits (genes). I.e., Mating 'Fortune’s Dearest' to 'Mort Morss' to select for stronger expression of teeth.
3. Phenotypic Assortative Mating {PAM} – This is crossing two plants that have the same look or trait, but are not related. This is used to attempt to concentrate extreme phenotypic expressions of the desired trait. I.e., Mating 'Mort Morss' to 'Tooth and Nail' to increase the expression of teeth.
4. Genetic Disassortative Mating {GDM} – This is when individuals with diverse genetics that are not closely related are mated. This is usually done to increase genetic diversity, and is often employed to create plants for future breeding projects. I.e., an example could be crossing 'Fortune’s Dearest' to any unrelated, edge-flowered (but not toothed) plant in the effort to ‘bring in new blood’.
5. Phenotypic Disassortative Mating {PDM} – This type of cross involves plants of different family lines that are outwardly different in appearance and is considered a wide cross to increase genetic (and phenotypic) diversity and is often employed to combine new traits. The first generation (F1) from such crosses are often what we call ‘bridge plants’ in the hobby and especially in the case of recessive genes, may not express the combined traits we are seeking in the phenotype, so must be carried forward to another generation to seek the recombinant individuals expressing all the desired traits. I.e., Crossing 'Mort Morss' to Tet. 'Priscilla’s Rainbow' to work toward a pattern-eyed and toothy flower.

As you can probably see, these five styles of mating encompass most of what we all already do in daylily breeding. I have made the effort to give an example of each that is related to breeding a popular trait in flowers, but as we discuss these systems, we will consider how these systems, already familiar from selection for flowers and other phenotype traits, applies to rust resistance breeding.

We will end here for now and in our next installment we will pick up with a more detailed discussion of these breeding techniques and how we might apply them to our goal of breeding for rust resistance...

Breeding For Rust Resistance in Daylilies: Part 4

Breeding For Rust Resistance in Daylilies: Part 4

In this fourth installment we will look at the importance of identifying recurrently resistant cultivars, the mindset required to make a good resistance breeder and the importance of exposure to pathogens in a resistance breeding program.

The Importance of Identifying Recurrently Resistant Cultivars

It is important when discussing rust resistance to first realize that there is no rhyme or reason to where resistance occurs. If one takes a wider view, of course, we could say that any cultivar that shows resistance likely had ancestral species (perhaps having evolved some level of resistance in the wild through interaction with the rust pathogen over an unknown amount of time) that carried some gene(s) for resistance and that from that point forward, each generation was passing those genes along until that cultivar encountered rust infection and revealed to us that it shows resistance. The same would probably be true of susceptibility. Yet, in the short term view, there is no way to know which cultivar will be resistant, even if we know it has an ancestor that is known to be resistant.

No specific phenotype traits seem to be linked with resistance. There is no way to know resistance or susceptibility based on foliage type, flower color, bud counts, branching, region of origin or even ancestry. Now, there does seem to be some tendency for certain colors to show more individuals with resistance than others (there are a lot of red cultivars that show resistance for instance), but there is no color where all the individuals are or are not resistant. There are resistant cultivars of every color and susceptible cultivars of every color.

Foliage type is also no indicator of resistance. There is no linkage between foliage type and resistance/susceptibility. Now, it is true that dormants will always have their leaves die off every year and that kills any rust mycelium living in those leaves, while an evergreen or semi-evergreen can have the mycelium survive even in fairly cold conditions, but that has nothing to do with actual resistance or susceptibility to rust.

As well, the entire notion of “hard dormant”, “dormant”, “semi-dormant”, “semi-evergreen”, “hardy evergreen” and “tender evergreen” is highly subjective. There may be some absolutes, but these categories commonly used in the hobby are more of a spectrum than a set of absolutes. For instance, I have purchased cultivars that are “hard dormants” where they were bred in locations north of me, only to have them display as “semi-evergreen” or even “evergreen” in my garden. 

As well, there are many examples of cultivars that are “evergreen” and “semi-evergreen” in southern climates that behave as “semi-evergreen”, semi-dormant”, “dormant” or even “hard dormant” when grown in northern climates. While the original species may in some instances be truly evergreen or dormant in all climates, even in some of those (fulva “evergreens” come to mind as do citrina clones) their foliage performance will depend a great deal on where they are grown. Since our modern cultivars are an amalgamation of many species, we can expect the genes of foliage type to be very mixed with great variability seen throughout the many climate ranges.

I would mention from personal experience that I have seen just as much susceptibility from northern dormants and semi-evergreens as I have from southern evergreens (or southern semi-evergreens or southern bred dormants, for that matter). In fact, I would say that susceptibility is much more normal from all locations than is resistance. In the first years of assembling a breeding colony of modern daylily cultivars, I bought a great many daylilies from breeders in the far north because I visually prefer the dormant foliage (all foliage types live well for me, but dormant looks cleaner and neater to me) and because I felt bad for all the northern collectors and growers who couldn’t get good dormants with nice, modern faces and I wanted to work on combining northern hard dormants with southern pretty faces in order to make daylilies that would be more useful for northern growers, but as soon as rust appeared, the vast majority of those hardy northern dormants rusted up and only got worse through the entire season. 

While their leaves died back that winter and the rust was gone, many of the plants were so weakened by the heavy rust of the previous year due to also having low tolerance that they performed very poorly with lowered fan number, bud counts, and branching the next year. As well, a great many of their seedlings were also highly susceptible, like having produced like in those cases. Most of these were removed from any breeding consideration with a few being used in salvage projects, while others that I retained are now here merely to use to ensure heavy rust to inoculate my seedlings when rust does appear.

With that said though, there have been a few northern bred daylilies that have shown excellent resistance to rust and I am using those heavily, so there is no way to say that “all southern daylilies are susceptible or resistant” or that “all northern daylilies are susceptible or resistant”. I would point out though that those cultivars from northern breeding that have shown good resistance often descend from other cultivars known to show resistance, even though no active selection for resistance had been applied due to lack of rust exposure. Further, I would also point out that I have obtained a great many daylilies from southern breeders that do show good to high resistance and are evergreen or semi-evergreen, but I have sought them out as there are many southern breeders who are making some selection for resistance in their breeding work, even if just through the very passive act of culling out the worst of their rust magnets, both in their breeders and in their seedlings. 

Both examples from north and south indicate that passive selection and removing rust magnets, rather than actively selecting for highly resistant or immune seedlings, can still be of benefit in a breeding program and that just the act of using a known resistant cultivar can increase the odds of producing rust resistance, even in situations where no selection pressures from rust infection are possible. So let us now consider the importance of identifying recurrently resistant cultivars.

In the years since rust has appeared in the US, there have been some small number of cultivars observed to not develop rust over a wide area of the country and for a long period of time. When this is the case, it is likely that these plants are strongly resistant and there is a chance that they may show resistance to more than one strain of rust. Nothing of that sort is proven, but the long term resistance seen in some cultivars, growing in many different locations, is encouraging and is perhaps the best point to begin in a quest for materials to use in breeding more resistant plants. Identifying such cultivars is a priority as while still anecdotal, numerous reports build a strong case toward the reality of their resistance. 

It doesn’t matter how old or simple the cultivar, though many may be neither old nor simple. All that matters is that those showing long-term resistance in many locations give the breeder a jumping-off point for potentially increasing the levels of resistance in their own seedling population. A further point is that when such cultivars also have many offspring that show recurrent resistance in many locations, we can then say that such cultivars and their family lines may represent a high level of breeding value for resistance.

Such cultivars, where they have been noted, need to be given more than a cursory glance. Even for a cultivar that is regularly immune to rust, one or more reports of some rust are to be expected. It is to be expected that even the most rust resistant may exhibit some level of rust sporation if there are other environmental stressors at work to lower their defenses. So we shouldn’t be too freaked out when the “proven resistant” cultivar shows up with rust in a given garden or a given year. Such a situation may also suggest that the individual has encountered a different strain of rust, and it is now confirmed that there are multiple strains of rust in the US.

Once large enough numbers of tests have been carried out in a wide range of conditions, an idea of overall resistance/susceptibility evaluation may be possible. In either case, I feel it is important to begin to identify truly, genetically based resistant individuals (as in ‘can reproduce the trait reliably’) and test them in both field and lab conditions to obtain further proof of their resistance, but most of all, I feel it is important for breeders to be using these cultivars and beginning to develop their own lines utilizing such individuals as part of their project base. 

The more anecdotal evidence that can be gathered, the better an insight we can gain into the rust resistance and potential breeding value of a given cultivar for rust resistance and this could then also build a foundation that professional researchers could use to establish proven resistance under proper controlled conditions. As professional researchers do more research, giving us a greater understanding of both rust strains and resistance factors, the greater our ability to breed for resistance will become, but at the same time, we mustn’t undervalue the observations of the hobbyist breeders. Both the anecdotal information of hobbyists and the empirical information of researchers are important in the pursuit of knowledge.

Without identifying those cultivars that actually show resistance, there is little clear direction for materials acquisition and breeding schemes to be formed. If there is genetic resistance to rust, then it will be heritable, and so determining those individuals that show the trait and can reproduce the trait is the first key in actively breeding for rust resistance. My experience and the information I have gathered from many sources (all anecdotes of course) have proven to my satisfaction that rust resistance has a genetic and heritable basis. This has not been ‘proven’ yet in any way by professional researchers that has been made available to the public at large, so only time will tell if we will have that ‘proof’, but I personally feel confident in proceeding with the certainty that there is a genetic basis to resistance. You, of course, will have to decide for yourself, but it seems that simply integrating one or two plants known to show high resistance in many areas surely couldn’t present a hugely undue burden to most breeders, unless their space was extremely limited.

There are many cultivars that have been stated to show resistance. Some of those reports are single-garden reports for one or more years. Other reports come from university studies. Some reports are derived from surveys and others come from scouring the Internet and daylily message boards as well as from personal communications. While none of this translates into “proof”, there are some trends that to me seem suggestive of actual resistance amongst some cultivars. There are a few cultivars that seem to show resistance in both field reports and university trials. I believe they may represent a jumping-off point for further testing and for hobbyist breeding projects. The scores for resistance do not always agree within all the tests, but there is an overall trend toward resistance in all evaluations of a handful of cultivars across several lists, and often with anecdotal reports lending credence, as well.

A final point I want to make in this vein is that I feel it is very important to work to identify newer and more modern types of daylilies that show good levels of rust resistance in order to have modern resistant material to work with and to cross to older resistant material to bring more modern traits in the resultant lines produced. Getting back to fully modern phenotypes will go much faster if there are very modern resistant cultivars to use from the beginning of such a selection project. Identifying even a tiny number of such cultivars would be very helpful and I am glad to say that some do exist. We will look at the issue of resistant cultivars in more detail in a later posting in this series.

Some Thoughts and Observations on Who Makes A Good Resistance Breeder

We could easily say that the best person to breed for resistance to rust lives in the deep south where rust is present the majority of the year, and that the person least suited lives in the far north where rust (is so far, nearly) never seen. However, that is not really what I mean by the title of this section. Instead, I want to focus in this section on what I feel is required, personality-wise, to actually pursue a program of selection toward disease resistance.

Beyond the observation and physical work required, my experience suggests that a certain mindset is required to pursue resistance breeding in an active fashion. That mindset requires focus and dedication, but perhaps the most important attribute required is detachment and/or a low threshold of sentimentality, and a large dose of practicality seems to help as well.

It seems to be ‘Murphy’s Law’ that your favorite individuals, the rarest individuals and the most expensive individuals, seem to show a higher frequency of low tolerance/low resistance to any given pathogen, regardless of the organism you are working with. For someone who is not very detached or is very sentimental, excluding such an individual from breeding may be emotionally very difficult if not impossible. Further, culling out such an individual may be unthinkable. With daylilies, culling out highly susceptible individuals may not really be necessary but excluding them from breeding, in many cases, may be. Exceptions would include such an individual being part of a ‘salvage project’ or in instances where northern breeders who simply can’t engage in a fully active resistance-breeding program and/or cannot fully or consistently test all their breeders and seedlings for resistance are pursuing a more passive system of increasing resistance.

With resistance breeding, maintaining highly susceptible individuals is important to keep a high level of rust in the garden for inoculation of each generation of seedlings, but it is also then important not to spray such susceptible individuals, or to at the very least not spray them in the fall. Even this may be more than some individuals can bear. As well, when a special individual seedling or cultivar is shown to have high susceptibility, it may be used in what I call a ‘salvage project’, which seeks to bring in the desired flower phenotype traits but recombined with resistance in a future generation (often not the first generation either). We will discuss this type of project later.

Beyond sentimental or very advanced cultivars, the culling of seedlings is a necessity. It is clear to anyone who has ever raised even a few daylilies from seed that you simply can’t keep them all. Anyone who has pursued daylily breeding with any seriousness will be used to culling seedlings, but they may not be used to culling seedlings with the most wonderful faces based upon plant traits. Rust is most certainly a ‘plant trait’ in that it does not make those beautiful faces any less beautiful, generally. It only disfigures the plant. So it may be very emotionally distressing to cull the most beautiful faces because a plant is rust prone and it may be equally distressing to not use plants in breeding that have exceptional flower traits, or that represent a heavy investment of cash, but after all, you can only really deal with so many salvage projects before you become overrun by the huge numbers of seedlings such work will generate. 

Resistance breeding requires a certain detachment to these things and an ability to drop sentimentality and cull where necessary and ‘salvage projects’ should remain special cases. Not everyone can do this and one must do some soul-searching before they begin to pursue such a program. The question one needs to ask oneself is, “Can I really cull and if so, can I cull or not breed from expensive, stunning, rare or advanced individuals?” If the answer is no, then perhaps this type of breeding is best left to those who can answer yes to that question, or a more passive program is most suitable for you.  

There is no shame in not being able to pursue such a program. In fact, I would suspect most breeders of any given organism wouldn’t find it easy. After all, who really wants to be immersed in disease and its unattractive manifestations when they can just ignore it or hide it with treatments and focus on beautiful flowers and/or other phenotypes? I want to stress that you need to be sure you can handle a resistance breeding program emotionally before you start one. Not everyone is cut out for it and that is fine. I have absolutely no judgment of anyone who isn’t. From my own experiences, I can attest that at times, such a program can be harrowing and emotionally draining, but in the end, is very worthwhile.

What I would suggest for those who do not feel up to undertaking such a project is that they simply attempt to keep informed about highly resistant individuals/lineages and incorporate those into their own breeding programs where possible. While this will not ensure resistance in all the offspring from such individuals, it does increase the likelihood that some resistance factors are entering those gene pools. This is the essence of a passive project, and while it isn’t resistance breeding, it is better than doing nothing and simply ignoring the problem. At the very least, you are educating yourself about what others are finding rust resistant, and you may even be able to send your seedlings south for further evaluation in very rusty settings, as well. If one or more of your own seedlings then turn out to show high resistance, all the better, and using such resistant seedlings of your own creation should not only be palatable, but joyful.

Finally, I want to stress that I do not advocate that all people should be following one goal or one system of breeding. We need diversity and it is the diversity of directions in the daylily world that has brought us the stunning and fast advances we see today. We need people who are just focused on the flower, creating advances that can then be incorporated into hardier or more practical lines, and we need people working on lines with more focus on plant traits including disease resistance. My point here is simply to instill an awareness of resistance and known resistant cultivars so that all breeders have more tools at hand regardless of their chosen direction.

Exposure Is a Necessity

Here is a point we need to look at for a moment. When breeding for resistance, it is important to have highly susceptible plants around to be certain your plants (cultivars, breeders and seedlings) are being exposed to sufficient levels of rust spores to ensure their inoculation. While a gardener who is not breeding may want to remove the most susceptible plants to ensure that they have low sporation, both to cut down on inoculation and to keep a more aesthetically pleasing garden, the breeder will want to do just the opposite.

I can’t stress how important this is, as some cultivars will not easily contract rust, even though they develop high spore levels when they do contract it. In some instances, a given plant may not develop rust unless it is given heavy exposure to spores, while others seem to literally suck rust out of the air and be dripping spores seemingly overnight. In order to identify those that are difficult to infect, but have high susceptibility when infected, they must be exposed to high spore levels. Thus for an effective resistance breeding program, there must be highly susceptible individuals maintained solely to ensure inoculation.

One of the great advantages in this for the breeder is that it then requires that some of the most susceptible be maintained. These can be those cultivars or seedlings with other good qualities that can be part of a salvage project, they can be sentimental favorites that you want to keep in spite of their high susceptibility or they can the expensive latest-and-greatest you just spent a fortune on only to find out they are highly susceptible rust magnets (and then maybe they can be a salvage project plant also).

This is probably the greatest difference between the breeder and the collector or average gardener in terms of how they manage the plants they grow. The collector and average gardener wants to reduce sporation, while the active resistance breeder wants to increase sporation to identify those that show the highest resistance under the highest level of sporation. However, for the person working with a more passive project, they may choose to not go to either extreme, not seeking to reduce or increase spore levels. As they are not actively seeking those with the most resistance under extreme spore conditions, but rather are just looking to remove those that are most susceptible under their garden conditions.

In the next post, we will begin to look at actual breeding methods, schemes and systems that can be used in the resistance breeding program...