Tuesday, December 23, 2014

Foliage Habits of Daylilies

Foliage Habits of Daylilies

Brian Reeder

Foliage habit is an interesting subject that I often spend a lot of time thinking about at this time of the year. I am in my garden every day, regardless of the cold or weather, as I have to feed and water my birds and that allows me to make observations of foliage type throughout the winter months.

An evergreen cultivar on the left and a true dormant cultivar on the right from my garden on 12/18/2014

To start this article, let’s look at how the AHS defines the foliage categories. From the AHS FAQ page we find the following:

What are the foliage traits of daylilies?

Foliage traits of daylilies include color, size, habit, and cold-hardiness and heat-tolerance.

The foliage of daylilies can be blue-green to yellow-green or any shade in between.

Daylily leaves vary considerably from slender and grass-like to husky, wide, and nearly corn-like. The leaves may arch, or may stand nearly erect. The length of daylily leaves ranges from as little as 6 inches to 36 inches or more.

The winter behavior of the daylily foliage is called "the foliage habit." For registration purposes, the foliage habit is loosely categorized as dormant, evergreen, and semi-evergreen.

  • Dormant. The leaves of these daylilies die completely back as winter approaches. They stop growing and form resting buds at the crown, and the foliage dies down naturally and gradually. In the spring, the resting buds have a distinctive spear-like appearance as they emerge.
  • Evergreen. These daylilies retain their leaves throughout the year. They do not form resting buds. Instead, they continually produce new leaves unless cold weather prevents growth. In mild climates, the leaves of evergreens remain green all winter. In the coldest climates, the foliage of evergreens nearly always is frozen back, but the crown survives if it is hardy (or well mulched).
  • Semi-Evergreen. Today, the term semi-evergreen is used to describe any foliage behavior that is not readily classed as simple evergreen or dormant. Originally, the term semi-evergreen (or conversely, semi-dormant) was used to describe those daylilies that retained many of its leaves and appeared somewhat evergreen when grown in the South, but lost all its leaves and went dormant when grown in the North.

Cold-Hardiness and Heat-Tolerance
The cold-hardiness of daylilies is quite variable. Some are ironclad hardy. Others are extremely tender. Cold-hardiness is not determined by the foliage habit. Evergreen, dormant, and semi-evergreen can be anything from extremely cold hardy to extremely tender. To avoid risk of losing a cultivar, choose daylilies that others have already grown successfully in your climate.
I think this is a very good description of the three foliage habit registration categories. I agree with the definition of dormant and evergreen and I think the description of semi-evergreen is particularly good in that it acknowledges this category as basically a catchall for anything that is not a true dormant or extreme evergreen. Further, the difference between foliage type and cold hardiness is defined.

It is a common habit of humans to generalize, and so we often hear generalizations such as ‘all evergreens are tender’ or ‘all dormants are cold hardy’, but these generalizations are not always true. There are cold hardy evergreens and tender dormants. It is important to remember this. At this point, the genes of the original species are so blended and recombined that almost any combination is possible.

I would also point out that in truth the semi-evergreen category is something of a generalization. There really is no such thing as a ‘semi-evergreen’ speaking from a genetic standpoint, though I don’t blame the AHS for using the category. It is a convenient generalization that is useful for registry and can encompass all the in-betweens in one classification. The only problem I see with the classification is that a lot of people seem to think it is a real thing that is absolutely definable, rather than a broad category with a lot of variation.

On the left is a clump of Ancient Elf, a true, hard dormant photographed in my garden on 12/18/14. It almost appears that there is nothing there and if you dig through it, the resting buds are almost completely underground. On the right is the same clump in bloom summer 2014.

In truth, there are only two foliage habits - dormant or evergreen. Anything that does not go completely dormant in the winter is an evergreen, technically speaking, though the 'evergreen' range is very variable. However, as daylily cultivars are hybrids of several wild species of daylily, the genes of those species are recombined into unique combinations in the hybrids and expressions that are not seen in the species can occur.

Those cultivars that we call semi-evergreen are likely the expression of both evergreen and dormant genes interacting within the one genome. It is highly unlikely that single genes control all foliage habits amongst the species and so there are probably major genes and minor genes (or modifier genes) at work to create the foliage habit expressions we see in the species and their hybrid descendants. It is generally accepted that evergreen foliage habit is dominant to dormant foliage habit (likely the action of some of  the ‘major’ genes).

So a semi-evergreen may be a heterozygote for both types of major genes with evergreen habit predominating but not fully expressing (this could also be due to a dosage effect), or we may see some instances where a homozygote for evergreen also has one or more modifier genes coming from dormant ancestors and thus don’t express the evergreen genes fully. There are also likely combinations of both examples. As well, there are undoubtedly homozygous dormant cultivars that have some evergreen modifiers and so are something of a ’semi-dormant’, being far closer to a dormant than anything else, but not a real, true, hard dormant. These frequently (though not always) get registered as ‘dormant’.

A true evergreen seedling (Substantial Evidence x Kaleidoscopic Intrigue) in my garden photographed on 12/18/2014

However, to fully understand the foliage habit of daylilies, it is important to give some consideration to the species from which they all derive. There are dormant and evergreen species amongst the Hemerocallis genus. The dormant species are mainly true dormants that perfectly fit the description for dormant as per the AHS. An example of this type is H. dumortieri.

The evergreens however, are a different matter. They are much more variable, ranging from the tender and fully evergreen H. aurantiaca and its clone Major to the group that I would consider ‘conditional evergreens’ such as the many clones of H. fulva, H. citrina. In these later species the foliage is usually evergreen in warm winter climates while going dormant in cold winter climates. It is also interesting to note the AHS description of semi-evergreen says this type of habit was the old definition of semi-evergreen. A few clones of some of the species can actually maintain evergreen foliage while forming a resting bud in cold climates. The fulva clone Chengtu is an example. 

Even in Stout's day, when they were only dealing with species and the very earliest diploid hybrids, it was noted that some of the evergreen species could not survive in the north, or did very poorly.

From Daylilies by A. B. Stout 1934, regarding Winter Injury on page 99 of the 1986 edition - "In the northern part of the United States and further north daylilies which have evergreen habit of growth usually suffer to some extent from winter injury...In the region about New York there is usually a protection of snow for only a small part of the winter and there is an alternation of freezing and thawing temperatures. When spring arrives many of the exposed leaves have been killed and some buds may be dead... The H. aurantiaca clone Major suffers so severely from winter injury that is usually does not survive the winter throughout the northern United States. Many seedlings obtained by hybridizing H aurantiaca and (its clone) Major with more hardy daylilies are not fully hardy."

On page 100 in the section 'In semi-tropical and tropical countries', he states, "In the southern states the types and varieties which are evergreen or nearly so, are said to be most satisfactory."

So from the very beginning, there was a noticeable difference in the most hardy, dormant species and the most tender of the evergreen species, with some evergreen species being impossible or nearly impossible to grown in the north. This is just a fact of the evolution of the species in their native ranges in Asia. We can't expect that all evergreen cultivars, descending from those semi-tropical evergreen species, are going to suddenly 'get hardy'. Some evergreen cultivars are very hardy, and probably due to cold hardy dormant species deep in their ancestries or from the presence of hardy types of evergreens such as H. fulva or H. citrina in their background. Others are not hardy and that has a lot to do with the genes they have inherited from tender evergreen species in their backgrounds.

Because there are different variations of evergreen foliage habit amongst the species, as well as the true dormants, and crossing these species widely made the hybrid cultivars, we have an even wider array of foliage habit expression in the hybrids than we do in the species. Some of our cultivars perform exactly as the species do in regards to foliage habit, but some fall in-between their species ancestors.

Foliage habit, in and of itself, does not touch directly on the subject of cold hardiness, as the AHS text above points out very well. Cold hardiness seems to be determined by genes other than those that determine the foliage habit, though those genes would also derive from the wild species in the ancestry of the hybrids. While it is true that there are hardy evergreen cultivars, it is also true that some evergreen cultivars will not perform at their maximum capacity in areas of cold weather due to the stress they must endure through the cold months of winter, even though they survive from year to year and bloom. An example of such suppressed performance would be reduced branching and bud counts or scape heights. There are however some evergreen cultivars that simply won’t survive in northern climates.

In my own experience with around 800 cultivars, I have only lost a tiny handful of evergreen cultivars outright to cold. What I see more frequently is suppressed performance, occasional loss of a few fans, reduced branching, bud counts and scape height. Because I am in an area that can be very cold or very warm in the winter, each year can be variable. However, my area almost never has the snow cover that more northern areas benefit from and so some evergreen cultivars are hardier both further north and further south than they are in my Kentucky garden. This can come as quite a surprise to folks not familiar with our variable winter weather and late, often devastating frosts.

A particularly bad combination here is cultivars that are evergreen and are early-early blooming. We frequently have late frosts, but we may get very warm as early as March and have full growth very early with scapes beginning to form on the earliest flowering cultivars by the beginning of May. When those late April and early to mid May hard frosts occur, this causes considerable damage to those early blooming evergreens and the entire first round of scapes may be completely destroyed or severally damaged. When those cultivars are also rebloomers, then the later bloom scapes will be fine, but for those first ones these late frosts are a disaster. There are very few years when we don’t have an episode of late frosts, so this damage is something I see almost every year. I do want to stress though that this does not mean these are ‘bad’ plants. I fully understand why the early-early evergreen cultivars are very desirable in more southern settings. They just aren’t the most suitable cultivars for my climate. In spite of that, I am still using some of these, especially strong rebloomers, in my breeding program. I am just careful about what I cross them with.

With that said, though, I want to stress that I buy and grow evergreens, usually bred in the deep south, making them a part of my breeding program and fully intend to keep growing them and breeding from them. While I personally prefer hard dormant cultivars, I want to produce plants that can be grown successfully in climates other than my own, both north and south. Another thing I keep in the back of my mind is that one can never tell how the climate may change over time and should we become warmer and warmer, hard dormants may start to be less viable here than the more evergreen cultivars. No one can know what will happen, and I certainly don’t claim to know, but I like to be prepared for all eventualities. Another thing that I take into consideration is that there is generally more information on the rust resistance of plants bred in the south than there is for plants bred in the north.

In my own garden there are very successful evergreens. I have grown Nivia Guest, for example, for over twenty years and it has never shown any problems. I would also point out that it is not a very early blooming cultivar, so I think this helps make it more successful as a garden flower, but the plant never reduces in fan count here in even the coldest winters. Other evergreens don’t do as well, and a few do really poorly, decreasing every year and showing infrequent bloom scapes only after the very mildest winters. However, some of these are still a part of my breeding program, even if only in a very limited way.

There are many reasons to use these cultivars. The southern breeders can go through their generations much faster than most of us in the north can (except perhaps where greenhouses are used in the north), and so the southern breeders are almost always ahead of everyone else in terms of flower trait advancements. Those advanced flower genetics are reason enough alone, but there are also other reasons. For me, the known rust resistance of some cultivars from the south is a huge necessity, as most northern growers can’t test for rust resistance so the results of their programs are far too often an unknown quantity. Finally, using the southern evergreens over northern dormants can often produce both foliage types, as well as the in-betweens so plants can be produced that may flourish in the south or in the north, and sometimes you get lucky and get a plant that flourishes in both extremes. Using the southern evergreens over northern dormants is a long-practiced, tried-and-true method. Just look to Curt Hanson’s amazing program if you need an example.

I have some evergreens here that survive (though certainly don’t flourish) and set seeds well, but their seedlings have very poor survivability through the winter in my environment. Those few that make it through though are often well worth the effort and usually continue to show hardiness. A technique I have found that is giving me some success is to use the pollen of these more tender evergreens on hard dormants that are very cold hardy to produce seedlings that seem to survive more frequently. Often all the seedlings are somewhere in the semi-evergreen category, but they may be more hardy and can often throw dormant offspring when backcrossed to other dormants.

I have no peer reviewed proof on this technique, and so far this is only my anecdotal experience, but it seems that when I take one of these more tender cultivar's pollen over a very hardy dormant as pod parent, I get better survival rates in the seedlings than I do if I make the reverse (reciprocal) cross. This may not prove to be true in all cases, but so far, this seems to be the most successful route in getting hardier seedlings from these more tender cultivars in my breeding program.

Now I want to turn to another aspect of foliage type. It is important to remember, especially for beginners, that all plants registered as a given foliage type may not always be that foliage type. Sometimes it is that a cultivar performs differently in your garden than it did in the hybridizer’s garden. Sometimes a seedling gets labeled wrong or information gets mixed up in the registration process. I don’t like to think that anyone is intentionally falsifying foliage habit for whatever advantage they may assume they get from doing that, but it is not outside the realm of possibility I suppose. I never assume that is the case though as I always give people the benefit of the doubt.

An interesting example - the cultivar on the right is a registered dormant, while the cultivar in the center is a registered semi-evergreen and the cultivar on the left is a registered evergreen. Can you tell any significant difference between any of them? I can't either... To me, these are all three in the 'semi-evergreen' category, with none being true dormants or true evergreens in my garden.

It is important to remember that there are species that are evergreen in warm winters and dormant in cold winters, and there are cultivars that perform in the same manner. When this happens, it is usually a happy surprise for all concerned, as such a plant registered as dormant by a northern breeder may prove to be evergreen in the south and vice-versa. More often it occurs that plants registered as semi-evergreen or evergreen by a southern breeder may turn out to go dormant when grown in the north. Both Linda Sierra and Priscilla’s Rainbow are examples of semi-evergreen and evergreen cultivars that go dormant in the north.

Priscilla's Rainbow - a registered evergreen that, as you can clearly see, goes dormant in my garden. This one is well known to go dormant in cold climates, but remains evergreen in warm climates. It has very tight resting buds that are mostly underground throughout the winter.

Another registered evergreen that goes dormant in colder climates, Challenger is a Stout cultivar from 1949 that is a blending of H. altissima and H. fulva, both of which show this type of foliage habit being evergreen in warm climates and dormant in cold climates.

What can be less exciting and desirable is when you purchase a ‘dormant’ only to have it prove to be some form of evergreen/semi-evergreen in your garden, if you really wanted a dormant (and I can assume the opposite would be true if you wanted an evergreen, but got a dormant instead). I have heard discussion that there are two types of dormancy - one is alleged to be temperature-triggered dormancy and the other is alleged to be light-triggered dormancy. If this is the case (and there is no solid proof that I know of that it is), perhaps the triggers for dormancy are very different in various areas and so something that goes dormant in one area may not get the right trigger to go dormant in another area. I can’t say, but I don’t want to think people are too fast-and-loose with their observations of the foliage habits of their introductions.

A situation that does raise my eyebrows a bit is when I receive a ‘dormant’ from a breeder in a very similar climate or not too far from me, only to have it remain green here through the winter. Maybe I am just enough further south of the grower, enough warmer, to not trigger full dormancy? I hope that is all it is. I also suspect that some growers have looser definitions of what a dormant is than I do. For me, if there is any green foliage still present during winter, then I don’t consider it a true dormant. One grower sent me a ‘dormant’ that remained fully green all winter, with foliage identical throughout the winter to Great White (an evergreen), which grew directly beside it. That was ok as it was fully hardy and bloomed late enough not to have any problems. I asked the breeder about this and the reply was, “Oh, yes, it remains green, but its leaves don’t grow at all in the winter and it shows resting buds, so it is a dormant.” 

While it is true that the H. fulva clone Chengtu shows leaves that remain green through cold winters yet develops resting buds, the cultivar I am referring to did not show what I would call resting buds, any more than did Great White, growing beside it. If it was a dormant then so was Great White. None of the evergreens growing here in a normal or hard winter grow new leaves (unless we have an occasional warm spell out of season) and a great many of them don’t have nearly as much green foliage above ground as this ‘dormant’ did. Further, it doesn't match the AHS registration definition of a dormant. I don’t grow this one any more because it turned out to be extremely susceptible to rust, but the foliage habit would not have been any deterrent to me buying or using the plant.

Center - a registered 'dormant' that is one of the most evergreen cultivars I am currently growing...

Foliage habit seems to be a continuum, moving from the true, hard dormant all the way to the true evergreen, with a range of variations in-between. For me, and based on the AHS definition of a dormant, it is only those cultivars that go fully dormant that are true dormants. However, there are cultivars that are probably genetically dormant while also having some small amount of modifier genes from evergreen ancestors and are close to the true, hard dormant on the continuum, but don’t express as true, hard dormants in many (most?) environments. These may be what some refer to as ‘semi-dormant’ and to me should be registered as semi-evergreens, rather than dormants, but it seems these frequently get registered as ‘dormant’. When I walk through my garden in the winter, I observe a good many registered ‘dormants’ with a bit of foliage sticking up out of the dead leaves. These are not the resting buds of true dormants, but are small fans with obvious leaves, even though they may be quite small.

Another problem is that in the far north, cultivars will go fully dormant that won’t even this far south, and may be full evergreen in the near tropical south. I always try to bear these many environmentally influenced variations in mind, as I don’t want to think badly of anyone or think anyone is being deceptive, and while that may make me have my head in the sand, it allows me to just shrug it off and move forward. After all, as a breeder, I can always work toward the foliage habit I want in my garden, in my own program.

Another thing that I sometimes hear, but have not observed personally, is there being any direct correlation between foliage habit and foliage quality. I have seen beautiful blue-green foliage on all foliage habits, and I have seen sickly, ugly foliage on all foliage habits. These variations in foliage color/quality seem to have nothing to do with foliage habit and are likely genes separate from the genes controlling foliage habit.

One final point that I want to touch on concerns foliage habit and rust resistance/susceptibility. I have been told by several northern breeders that their cultivars are ‘likely resistant, because they are good hard dormants”, the implication being that only evergreens are rust susceptible. This is absolutely false. There is absolutely no linkage what so ever between foliage habit and rust susceptibility/resistance. I have cultivars of all foliage types that show strong rust resistance, and I have cultivars of all foliage types that show rust susceptibility. I can assure you that foliage habit has nothing to do with this and neither does foliage color or cold-hardiness/tenderness. The genes of resistance/susceptibility are not the same genes as those that determine foliage traits.

I will say that I actually have more highly resistant evergreen and semi-evergreen cultivars than I do resistant dormant cultivars. Again, this has nothing to do with foliage habit. I suspect this is because breeders in the south have had to contend with rust now for over a decade and so they have been able to evaluate cultivars for resistance (so there is some information on these available) and some few breeders in the south have actually been breeding for rust resistance now for a good long while. Conversely, cultivars in the north are not being evaluated for rust resistance with any frequency nor is much selection for rust resistance being done in the north.

In defense of northern breeders, this is understandable, as they don’t have the conditions to evaluate for rust, but it does mean that northern cultivars are thus an unknown quantity in this regard. So my experience points to there possibly being more susceptibility amongst many hardy, northern dormant lines by default, than there is amongst some of the lineages (but certainly not all!) of southern-bred evergreens and semi-evergreens, but this has nothing to do with foliage habit and rather is caused by environmental constraints and chance.

In closing, I would like to encourage people to talk about the subject of foliage habit. I know some people get offended, but these things are just facts. We in colder climates don’t say that some evergreens do poorly, or don’t perform to their full potential, to offend people. Dormancy is not a marketing scam (I have actually been told that!), nor is it an attempt to vilify those breeding evergreens. Every foliage type is important and necessary. Not every plant will prosper in every garden. This is a simple fact of life. Sometimes that is related to their foliage type/cold hardiness, and sometimes it isn’t. When someone in the north relates that a given southern-bred cultivar has done poorly in his or her garden, being harmed or killed in the winter, this is not an attack on the breeder of that plant. If I introduce a hard dormant and a southern grower buys it and it dies, quickly or gradually, I know that many hard dormants often don’t survive in warm areas, so I can’t take that personally. Why should the reverse situation be any any different?

I fully understand why southern breeders focus on evergreen/semi-evergreen foliage and I understand why northerners tend to focus more toward dormants. I don’t in any way blame southern growers for growing and breeding the foliage that works best for them. Why on earth would they not? I grow and breed what works best in my garden, as should everyone else. Further, it seems intuitively obvious to me that no southern breeder can know beyond a shadow of a doubt how any of their introductions will behave in cold climates until they have actually been grown in cold climates in many parts of the continent, and they should be aware that there are instances where a plant is hardier in the far north with constant snow cover all winter than they might be in less cold areas where there is not a constant snow cover and where temperatures can fluctuate a great deal. Conversely, the same can be said for any plant bred in the north in regards to its ability to survive and flourish in the south.

It is only by exchanging information and our experiences that we can start to gather a broad base of information to help people in making proper cultivar choices for their area. I would think this would be important to all of us, because successful gardeners are probably going to stay with it longer than people who constantly have failures due to poor cultivar choices for their area. I hope that this post can help to generate a civil and friendly discussion and that we can share our information and experiences without hurt feelings or angry responses and through that sharing only improve our understanding of, and success with, our beloved daylilies.

Tuesday, November 18, 2014

A Review of Identification of Pathotypes in the Daylily Rust Pathogen with an Eye Toward Breeding for Resistance

A Review of Identification of Pathotypes in the Daylily Rust Pathogen with an Eye Toward Breeding for Disease Resistance

Brian Reeder

Overview of Paper

In the paper entitled Identification of Pathotypes in the Daylily Rust Pathogen Puccinia hemerocallidis - James W. Buck (Department of Plant Pathology, University of Georgia, Griffin, GA 30223, USA - Received: January 23, 2013; accepted: May 16, 2013.  - Journal of Phytopathology 161 (2013) 784–790 - 2013), the abstract at the beginning of the paper states... 

"Daylily rust, caused by Puccinia hemerocallidis, has been present in the United States since 2000. In 2003, inoculations with a single isolate of P. hemerocallidis identified daylily cultivars with high levels of resistance to the fungus. The present study was carried out to determine if pathotypes of P. hemerocallidis are present in the southeastern United States. Sixteen isolates of P. hemerocallidis were each inoculated onto leaf segments from 19 daylily cultivars and the resulting disease phenotype assessed. A significant effect of rust isolate on host reaction phenotype was observed for nine of the 19 daylily cultivars. Five of the nine cultivars displayed reaction phenotypes with different isolates of P. hemerocallidis that included at least one susceptible or moderately susceptible and also resistant phenotypes. These results indicate that different pathotypes of the fungus are present in the southeast United States. Daylily hybridizers interested in screening for host resistance to P. hemerocallidis will need to include multiple isolates of the fungus to allow for this host specialization."

We can see from this statement that we now have good evidence that there is more than one strain of rust in the US, but there also seems to be more than one gene for resistance to the potential strains of rust pathogen studied in the paper.

The paper gives an overview of the methods used. The research is conducted in greenhouses for quarantine of each isolate. Each isolate may or may not be a unique strain of rust. I have received no data showing any gene typing of each isolate. To my knowledge at this time, the isolates are determined by unique accession. That is, each isolate came from a different garden, so that there were 16 accessions from sixteen Georgia gardens in the study. To the best of my knowledge at this time, all evidence of strain differences in rust accessions is based on the reactions of the host materials. So at this time I would stress that the most we can know from the paper is that it seems highly that there are at least two different strains of rust amongst the 16 isolates, though there could be more than two.

The same can be said for any hypothesis of ‘resistance genes’ based on this paper - there seems to be the indication of variation in resistance amongst the nineteen cultivars used in the research project. Of those nineteen, nine show different responses to the 16 isolates and of those nine, six were observed to have a wider divergence in rust presentation with reactions that were both resistant and susceptible, depending upon the isolate. As the most common type of apparent resistance variation is expressed as one rating up or down (i.e., HR to R or R to MR or MR to MS), those cultivars that show a wider jump between rating variations (i.e., R to S) are notable and may indicate actual strain differences in the rust pathogen as well as variable resistance/susceptibility genes in the host (daylily plant). However, as breeders, we may be more interested in those cultivars that showed the highest resistance to every isolate, as these may represent individuals with more than one resistance gene or with a resistance gene offering protection against more than one rust strain. Both instances could be useful in breeding for resistance.

These quotes of interest caught my eye in the paper’s Discussion section. I will quote each here and offer a bit of commentary.

In conclusion, the present study clearly shows that pathotypes of P. hemerocallidis that differ in virulence to daylily cultivars are present in the south east United States.

This is accurate. We can now make a fairly good case for there being more than one strain of rust. Further work may reveal much more about this, if any of the research being done is published or made available to the hobby in some form.

The number of resistance genes to P. hemerocallidis present in Hemerocallis sp. is unknown. Diploid and tetraploid cultivars, with dormant to evergreen growth habits, were included in this study with no apparent differences in susceptibility observed. The chrysanthemum – Puccinia horiana pathosystem is thought to contain at least seven resistance genes (De Backer et al. 2011). Incorporation of disease resistance into new daylily cultivars would be a valuable tool for reducing the impact of daylily rust on the ornamental industry… Development of DNA markers that can detect resistance in diploid and tetraploid Hemerocallis germplasm could greatly facilitate current breeding efforts… Daylily hybridizers interested in producing new cultivars resistant to P. hemerocallidis will need to include multiple isolates of the rust fungus to allow for this host specialization.”

This well surmises where the hobbyist breeder with an interest in increasing rust resistance in their gene pool now finds themselves. We can be relatively certain that there is more than one strain of rust in the US. We know that there are resistance genes to rust pathogens in other species. We know that such genetic resistance can be vertical (single dominant major genes) or horizontal (multiple genes combined).  

We have seen fourteen years of data, both scientific research and anecdotal observations, which allows us to surmise that there are genes for resistance in the daylily gene pool and we can make use of any such genes in our own field selection programs for rust resistance. Identification of resistance/susceptibility genes with laboratory methods is not currently available to the hobbyist breeder. There is no way to know if such testing will ever be made available or if it will be kept as a proprietary intellectual property. In the mean time, the hobbyist simply needs to do what we have always done, and breed best to best using what data we can find, what research is made available and our own observations.
Prairie Blue Eyes

Discussion of Practical Applications

So how do we hobbyist breeders apply the information gained through Dr. Buck’s paper? What is actually applicable to us? For me, the most important take-away is something I had previously taken for granted anyhow - there is not just one ‘rust’ pathogen. We will generally note variations in response in any given cultivar based potentially upon both environmental factors and/or strain interactions. Of special interest are those cultivars that show high resistance in many locations and over many years. It is possible that, if multiple genes for resistance occur in the daylily (which seems likely), then there are individuals that, quite by chance, already have more than one gene for resistance combined into their genotype. Such individuals would be highly useful in any effort to breed for resistance. Even if a new, more virulent strain of pathogen arises that defeats the resistance of any of these long term resistant individuals, they are still useful breeders for the resistance they convey to other strains of the pathogen. In short, such cultivars may be useful for a gene-pyramiding project.
Joan Senior

Discussion of Most Resistant Cultivars

For brevity, in considering the cultivars in the study, I will focus on those six cultivars that showed the highest and most consistent resistance with no susceptibility ratings in Dr. Buck’s paper - Hush Little Baby, Joan Senior, Prairie Blue Eyes, Going Bananas, Stella De Oro and Mardi Gras Parade.

It is by chance that I grow and have grown all six of these cultivars for a long period of time, some as long as thirty + years. It is also by chance that I had identified each of these cultivars as showing strong resistance to rust in my own field observations and so have been using them in breeding for several years already. I am already into the second generation with some of these cultivar’s descendants and I am seeing, what suggests to me, heritability of that high resistance. I believe any of these cultivars can offer a base upon which to add more resistance genes through outcrossing to other cultivars that also show high resistance. It is a place to start.

Now I know the arguments. These are all plain, old, cheap cultivars, so why would anyone want to use them? Stella De Oro, after all, is universally disparaged and seen as a near blight by refined daylily personages. However, my own breeding tests show that ideas of “old” or “plain” are more in the mind of the person thinking the thought. By combining modern faces and advanced phenotypes onto these older cultivars, new advances can be seen that were not possible back in the day when the cultivars were being bred from. By dipping the best of now back into the best of before, advances are possible and this also allows us to keep identifying potentially resistant new daylilies to make intensified gene combinations by breeding them back onto older, more proven cultivars. Both advanced faces and plant traits can be selected for in one program, after all.
Stella De Oro

Uses in Breeding Programs and Methods

We would typically suggest that individuals showing broad resistance, much as the six I detailed above, might have ‘vertical’ resistance, while a plant showing less complete resistance may show ‘horizontal’ resistance, but things may not always be so cut and dry. There can be instances where vertical resistance may give resistance to only one specific strain, or there may be instances where a single gene infers resistance to multiple strains. Conversely, horizontal resistance, being quantitative, can fall anywhere on a spectrum, depending on the concentration of genes in any given individual. In instances where many resistance genes are combined into one individual, we may see resistance to multiple strains. In some instances, this can be perceived as ‘vertical’ resistance, especially where the resistance is very complete. 

Gene Pyramiding is a concept in genomics that involves stacking multiple genes for resistance into one genome. While pyramiding is in many ways similar to the concept of horizontal resistance, in that there are multiple genes concentrating greater resistance, the difference is that in pyramiding we are making a conscious effort to add as many resistance factors as we can, possibly also tolerance and slow progression of sporulation traits, into one individual to increase field performance against the rust pathogen(s).

Some might suggest that a path would be to inbreed each of these six cultivars from the research paper and to thus concentrate their own resistance genes into homozygous lines, and this would certainly be interesting from a research standpoint, but from a hobby standpoint, I think this is one of our least productive routes for many reasons.

Another potential route is to cross the six cultivars from the paper to create lines of concentrated rust resistance. While this is feasible, and certainly could be interesting, I think it has two major drawbacks. The first is that none of the six cultivars offer anything terribly modern from the point of view of the flower. The second is that we do not know how many resistance genes may or may not be contained within all six of those cultivars. So strictly relying on those six cultivars, and only those six cultivars, is much too limiting for most modern breeding programs.

I believe the most productive route is for each breeder who has the interest to use some of these six cultivars and to combine them with their own favorite cultivars, seedlings, and interests in form, color or pattern, especially those alternate cultivars that have also been shown to have or are known to have some resistance themselves. In other words, these six cultivars would possibly have applications both in pyramiding with other resistant lines as well as being useful in salvage projects to bring desired flower traits into more resistant genetic backgrounds.

First, let us look at using any of these cultivars in salvage projects. I believe that it is this type of breeding where the most interest is likely to be found in the daylily world, as a number of remarkable and popular cultivars show various levels of susceptibility. The desire to salvage the good traits into a more desirable background setting is standard fair in ornamental plant breeding and daylily breeders have been doing this type of thing as long as daylilies have been bred.

In short, a salvage project is a cross of highly resistant x less resistant/more susceptible. This cross is done to bring the expression of resistance together with desired flower traits in the F1 and/or later generations. Generally, a field test of F1 offspring will reveal some with higher resistance. Select toward resistance where possible. The F1 can then be interbred, backcrossed to the more resistant parent or outcrossed to another resistant cultivar or seedling. Selection is toward resistance in at least the second generation (F2, Bc1, etc.), if not the first (F1). From this technique, plants of usable resistance can be secured for further breeding work and in some instances, resistance may be increased even in the F1. Salvage projects may become a very important aspect of daylily breeding for spreading resistance genes further through the gene pool, but it is not the most important method for increasing resistance within individuals.

The most important form of breeding for increasing resistance genes within given individuals is to stack multiple genes for resistance together through the pyramiding of genes. We do this by breeding resistant individuals carrying different genes (or suspected different genes, in the hobby setting) together. We are seeking to combine the different genes from each parent into the offspring for broader-based, multigenic resistance to the given pathogen in future generations. We may expect to see some progress in the F1, selecting those that field trial with the most resistance or we may see little to no increase in the F1 and seek more expression in the F2 and later generations. Much will depend on the nature of the genes involved.

Regardless, we have many options once we have our F1. In my own situation, I prefer to field trial such seedlings for resistance levels. I then select for acceptable expressions of field resistance. I may repeat this for one or more years before I ever begin breeding. Once I begin breeding such F1 plants, I might go in any of many directions. I can backcross to either parent to concentrate that particular form of resistance, making a BC1 generation. This can often be a wise thing to do in both directions. Another thing I can do is to interbreed the F1 to make an F2. This is the best way to find the new recombination of both forms of rust resistance in one plant. Whether we need to breed to full homozygosity for any/all of the resistance genes will depend on their penetrance and their nature (dominant/recessive). Finally, the F1 can be outcrossed to other lines, cultivars or seedlings, in an effort to combine the resistance of both parents with another type of resistance. This later example tends to only work well when dealing with highly penetrant dominant genes, typically. 

As you can see, there are many directions and possibilities for our F1 seedlings. Our main aim is to combine the genes for resistance from both parents into the offspring. Once we have a plant or plants (whether as an F1 expression of dominant genes or in the F2) that show the targeted combination of traits we are looking for, we can then move forward. We may choose to work within the line to concentrate traits or we may seek to further build our pyramid by going out to a different lineage, also showing resistance, in the hopes of adding yet another genetically distinct set of genes for resistance.

Pyramiding of genes can go on indefinitely, so long as there are new genes to add. When an older, proven cultivar seems to ‘fail’, it may well be that it has encountered a new strain of rust that it does not have resistance for, so such cultivars should not be discarded, but used in pyramiding with new resistance genes to the new strain of rust to keep building a broad base of genetic resistance. The cultivar reacting to a new strain of rust that has been resistant for many years, through many tests and in many locations in the past has not suddenly ‘lost’ its resistance. It still has resistance to the rust pathogen strains it was previously tested against and those genes can and should still be put to use. 

Over time, we can assume that any and all genetic resistance will fail as new strains of the pathogen emerge. The speed at which this will occur is anyone’s guess, but with time, that failure is inevitable. Rather than see this as a problem, through pyramiding of resistance genes, we can continue to build on past successes and resistant bloodlines. In this way, we incorporate a broader range of resistance so that plants can safely overcome the challenges of many strains of rust. 

An excellent place to start will be to make some use of those cultivars that have been tested in research projects (such as that detailed in the Buck paper) and field trials, as well as those with a number of anecdotal reports and personal experiences. Some of the six cultivars with the highest scores in the Buck paper should find a place in any and all diploid breeding programs. As well, tetraploid conversions exist of several of these six cultivars. 

We will look more in-depth at some of these six cultivars in a coming blog post.
Hush Little Baby

Thursday, January 30, 2014

Breeding for Rust Resistance in Daylilies: Part 12

Breeding for Rust Resistance in Daylilies: Part 12

In Conclusion

So now we come to the final post in this series. In the previous eleven posts we have looked at a wide range of subjects relating to rust and selecting for rust resistance in daylily breeding programs. It is my hope that these posts have been of benefit to you and that some few of you who have read them may now make use of some of this information and apply some of what I have offered herein to your own breeding programs. 

I would like to make a short review of what I consider to be the most important points made throughout this series.

1. Rust is now an inescapable reality on the North American continent. We have it, so there is no going back to the old pre-rust days. Even for those in climates cold enough to kill all foliage and suppress rust each winter, rust may still enter your areas through shipped daylilies or through the use of greenhouses. For those of us in warmer climates, even when an exceptional winter suppresses rust for one year, rust is still a reality and no single harsh winter is going to permanently eliminate rust. Rust is a reality we all face and the further south you go, the more persistent that reality is and the more extreme the impact.

2. There is resistance to rust in the daylily population. While resistance levels will vary from cultivar to cultivar, and may even vary from garden to garden or year to year, depending on the environmental factors at work and/or the strain of rust present, there is some consistent resistance amongst some cultivars and that resistance appears to have a genetic, and thus heritable, basis.

3. As rust resistance appears to have a heritable basis, active breeding and selection for rust resistance can be practiced. Simple Mendelian segregation ratios should not be expected, and we should be realistic and look for individual resistant seedlings, rather than being focused on a more idealistic goal of developing "resistant lines". While there is some circumstantial evidence that some family lines do exist that show higher than average percentages of resistant individuals, a more realistic and basic breeding goal is to simply select resistant individuals. Equally important is the reduction of the use of very susceptible individuals in breeding programs, except perhaps in 'salvage programs'. Finally, of equally great importance is the reduction of the number of susceptible individuals that are introduced as cultivars and put on the market.

4. It is important to remember that the term 'resistant' it not synonymous with 'immune'. They are different things. Further, 'susceptibility' and 'resistance' are broad terms that do not simply define one particular phenotypic expression, but represent a bell curve of phenotype variations with the two terms representing the extreme ends of the spectrum with many variations in between. Further, tolerance means the ability to tolerate the presence of rust without severe repercussions and lack of tolerance means those that suffer severe repercussions due to the presence of rust that can range from suppression of vigor to death in some specific environmental situations.

5. There is known to be more than one strain of rust. Rust will continue to mutate, but it is highly likely that one cultivar or another may show resistance to any given rust mutation. A daylily resistant to one strain of rust is valuable for breeding even if it shows lack of resistance to another strain of rust. The ultimate goal would be a layered or pyramidal resistance that combines multiple forms of genetic resistance into one individual. 

6. You need to make observations in your own garden when rust appears and develop your own observational system and approach to breeding and management based on your own experiences. The information I have imparted to you in this series is my experience, my basic approach or system and the gathered anecdotal and peer-reviewed information that I have been able to find. This information is presented to give you a jumping off point, tools to help you develop your own approach, for use in developing your own program based on your needs, interest, and available space and time. The information I have presented here is not set in stone. 

7. Any cultivar listed as resistant, immune, susceptible, etc, is merely a guide and may not apply to all situations or all strains of rust. You need to find what is best in your situation and work from there. Further, a cultivar that shows excellent resistance in one year, but susceptibility in another, may have encountered different environmental conditions or a different strain of rust. Don't be too hasty in eliminating a cultivar from your program due to variability between its response in one year or another. A better view is gained of resistance if the cultivar is observed for many years in one particular setting. Any list of resistant cultivars is merely suggestions and is presented as a guideline and no cultivar therein will be resistant permanently in all settings or all years. 

8. There is considerable difference between the approach of an average gardener, a collector, a seller and a hybridizer. Each will have different needs and may also have different approaches. The average gardener may choose to eliminate susceptible cultivars and may want to focus on only maintaining resistant cultivars in order to not have to spray and to keep a neat and attractive garden setting. Collectors and sellers may choose to maintain susceptible cultivars and may also spray, with sellers in most states being required to spray, at least for part of the year. Hybridizers who have any interest in increasing resistance to rust in their program will need to maintain susceptible cultivars, but are advised to not breed from such any more than is absolutely necessary (salvage projects). While hybridizers who are also sellers may be required to spray, those who can forgo spraying are in the best situation to observe actual resistance levels and make selections toward resistance.

9. Your location will determine how you will approach your resistance breeding project. Those in the most rust prone areas, where rust is present in spring and fall, have the very best environment for rust resistance selection. They can engage in an active resistance breeding program. Those in less rust prone areas or in the far north (and who do not use a greenhouse) are less able to actively select for resistance and are usually only able to participate in a passive program.

10. An active resistance selection program requires rust (at least in the fall and better if in fall and spring) yearly and requires no spraying so that all plants are equally exposed to rust and can reveal their resistance levels. A passive program involves the use of known resistant cultivars as breeders, rust present in the garden on occasional years, no spraying when rust does appear and active observation and notation of the performance of the resistance levels of the cultivars and seedlings in the garden with the use of the most resistant in the breeding program. Passive programs may also send seedlings into more rusty environments for testing and the gathering and recording of anecdotal evidence from those growing the plants from that program is also important. Finally, in a passive program, it is very important to keep up with information on resistant cultivars and advances in research as well as exchanging information with other breeders.

11. Greenhouses are an excellent way to keep rust active in a northern program and can allow a northern breeder to maintain rust for an active resistance breeding program.

12. Sprays will suppress the formation of rust spores, but do not kill rust. Some sellers are required by law to spray. This is unfortunate, but unavoidable where that is the case. As spraying does not kill rust, but only suppresses spore formation, any plant can still carry rust even if sprayed to control rust. As sprays are expensive and environmentally questionable, I do not advocate spraying for anyone who is not legally required to spray. I would recommend anyone who does use sprays or is considering using sprays to look into some of the side effects on the environment and beneficial insects of fungicides. Recent research suggests that many fungicides may play a role in bee colony collapse syndrome among other problems. This makes spraying even more questionable to me, especially since spraying does not kill rust, but only suppress spore formation. You will have to decide where you stand for yourself.

13. Keep researching. New information appears. Keep on top of it. This is especially important for those engaged in more passive programs.

What I have presented here in this series is a starting point. I have presented you with tools to use in developing a resistance breeding program, passive or active, of your own. However, this is not the final word, nor is it comprehensive. I have shown you my thoughts, feeling and observations - shared my methodologies and understanding. Now you need to develop your own.

I hope that even a few who have read this series of posts takes this information seriously and begins to apply even a small amount of it in their own programs, but I can't force you to do that. All I can do is lay out the basic points and then you have to pick up the ball and run with it. Most of you probably won't. It is too easy to spray, or ignore it, or feel that your cold winters insulate you from concern, but if even one for every thousand readers makes some effort, that is more effort than was being made before.

I believe that in time, this subject will become unavoidable for all of us, but I also hope I am wrong. Time will tell. I know that selection produces results. I also believe that those who do not ignore rust and who apply even some of the information I have presented in this series will be ahead of the curve and will be better prepared if we do see a rustier and rustier future. I leave it to you now to do what you will.

Tuesday, January 21, 2014

Breeding for Rust Resistance in Daylilies: Part 11

Breeding for Rust Resistance in Daylilies: Part 11

This installment will offer a list of links to websites, as well as a couple of books and a movie, that I think are of value in learning more about daylily rust, breeding for resistance to diseases in plants and plant rusts in general. This is not a complete list. There are many more sources of information on rust, breeding and genetics and the Puccinia genera. I would encourage anyone interested in any of these subjects to constantly research. New information can emerge at any moment. 

References and Recommended Reading

Specific Information Regarding Daylily Rust

Resistance of Daylily Cultivars to Daylily Rust Pathogen, Puccinia hemerocallidis - HortScience 38(6):1137-1140, 2003, Mueller, Williams-Woodward, Buck. University of Georgia, Department of Plant Pathology
(Includes a list of resistant cultivars)

Microscopic and Macroscopic Studies of the Development of Puccinia hemerocallidis in Resistant and Susceptible Daylily Cultivars
Li, Windham and Trigiano, Dept. of Entomology and Plant Pathology, University of Tennessee, et al., 2007
(Includes a list of resistant cultivars)

Arkansas Daylily Rust Rating Field Study
(Includes a long list of resistant cultivars)

Cornell PDF on Daylily Rust
(Includes a list of resistant cultivars)

Daylily Rust Information Page 
(Sue Bergeron’s Website - a great source of rust information online all gathered in one place)

AHS Daylily Rust Page
(A good general page on rust)

Mark Carpenter’s Rust Information Page at the Lily Farm Website
(Viewpoint and advice from a large southern breeder with good information on sprays)

APSnet Daylily Rust Page

Daylily Rust Yahoo Group 
(Run by Sue Bergeron and another good source of information in the archives and a place to ask questions)

Maurice Dow’s Site on Daylily Biology and Genetics
(A very informative site focused on daylily biology and genetics. Maurice further elaborates on his AHS Journal articles here also. Very interesting!)

Breeding for Resistance to Diseases in Plants and General Plant Genetics

(An excellent overview of resistance breeding in plants)
Print version ISSN 0100-4158

Principles of Plant Genetics and Breeding, George Acquaah, Blackwell Publishing. ISBN 987-1-4051-3646-4.
(This is an excellent book. You may need to filter out the industry propaganda and academic biases, but it is an excellent book non-the-less. I highly recommend it)

Breeding Plants for Disease Resistance: Concepts and Applications - R. R. Nelson
(An older book, but actually excellent for that very reason. Written before the advent of modern lab techniques, this book focuses on actual breeding methods for increasing resistance in domestic populations)

Michael Pollan - The Botany of Desire
(This is a fantastic book and movie that looks at the domestication and breeding of four genera of domestic plants. The sections on apples and potatoes are particularly relevant as there is considerable discussion of disease resistance breeding in both of those sections)
-PBS site about the movie
-Amazon Page for the Book

Rust in Other Species

Puccinia Page @ Wikipedia
(A nice short overview of Puccinia)

USDA Cereal Rust Page
(Lots of information on rust in cereal crops)

In the next and final installment of this series, I will review the points we have touched on in this series as well as looking at a few final points I would like to mention.