Monday, August 20, 2018

Breeding and Selecting for Daylily Rust Resistance

Breeding and Selecting for Daylily Rust Resistance

Anecdotes From One Gardener's Experience

Brian Reeder

Originally published in Vol. 73 No. 1 Spring 2018 of The Daylily Journal  for The American Hemerocallis Society

A susceptible daylily showing heavy rust sporulation in front of a highly resistant cultivar showing beautifully green, clean foliage.

Daylily breeders have observed instances of resistance to rust since the fungus was first reported the United States in 2000.  Field tests, lab tests, anecdotal reports and breeding tests all indicate that there is a genetic basis for the breeding and selection of rust resistance.
My personal experience suggests that by breeding with very high and high resistance cultivars a high to very high level of resistance is possible to obtain in the seedlings. Cultivars and seedlings that have consistently been shown to exhibit very high resistance by repeated tests, when bred with each other, can produce a good percentage of high to very high resistance offspring, sometimes up to 50%+ very high resistance seedlings. Crossing high and very high resistance plants to less resistant plants can still produce some high resistance seedlings, though the percentage varies and is typically lower than in the previously described breedings.

ZIGGY PLAYED GUITAR is one of my 2018 introductions that shows Very High resistance to rust (A+ rating), and showed that level for all five years of my rust screening program. It has also produced numerous seedlings showing this level of rust resistance.



My garden is located in Southeastern Kentucky, zone 6. My interest in hobby breeding of plants and animals goes back to early childhood. Among many other plant species, I have grown daylilies for over forty years. I was a precocious child, corresponding with many adult hobbyists and scientists, which led to me being mentored in husbandry and genetic sciences by a few truly exceptional individuals. One of those mentors introduced me to genetic disease resistance and that concept has never left me, only growing over time as I have seen the importance of this oft-neglected aspect of breeding and selection.

Seoul National University, NA 54920
My work with breeding focused on animals (specifically poultry, but also goldfish, colubrid snakes, etc.) from childhood up to 2008, with resistance to disease always being a major focus. I had started breeding daylilies in the late 1990’s, but my work with poultry didn’t allow the time to develop an active program.

SUBSTANTIAL SUBSTANCE is one of my 2018 introductions. A cross of STELLA DE ORO and SUBSTANTIAL EVIDENCE, it showed Very High resistance (A+) through all five years of my rust resistance screening program.

My first experience of daylily rust was in the fall of 2001 after purchasing some daylilies from a local box store. That year I noted that a few of the daylilies I grew (Frans Hals, Chicago Apache, So Lovely, Stella De Oro) seemed to show no rust when surrounded by heavily infected plants. Winter killed the rust that year and though I moved on with other projects, I didn’t forget that observation. When I chose to actively breed daylilies in 2008 I knew that rust resistance would be one trait I would want to consider, along with other plant and flower traits.

SUBSTANTIAL RETURNS is one of my 2016 introductions. It is a full sibling to SUBSTANTIAL SUBSTANCE and SUBSTANTIAL GLOW. It is another of my introductions that showed Very High resistance (A+) throughout the screening process.

My Experiences with Breeding and Selection for Rust Resistance

Starting in 2008, I spent two years searching for the scarce information about daylily cultivar rust resistance and resistance breeding within the Hemerocallis — before I purchased any new plants. I realized that I would have to screen plants on my own to make some assessment of resistant individuals, while continuing to search for information from other sources.
I made no special attempt to bring rust into my garden, expecting it to arrive of its own accord. I was surprised to not have a rust outbreak until early August of 2012. Once rust appeared, I then set in motion a five-year screening and breeding evaluation program. Because rust does not survive my zone 6 Kentucky winter, I was forced to bring in numerous plants each spring from gardens with endemic rust to ensure the presence of the fungus for screening purposes.
In 2012 I did weekly evaluations of resistance/susceptibility levels, recording the results. I utilized a basic rating system in 2012 with four rating levels, plus an additive level for very high resistance plants that show no visible symptoms of rust.

LAVENDER FEATHERS is one of my 2016 introductions and showed Very High rust resistance (A+) through all five years of my screening program. It also throws many seedlings in the High and Very High rating level. This cultivar demonstrates that highest resistance can be achieved with very modern styles of daylily flowers. This is also an instance that demonstrates that parents of lower resistance that carry resistance genes can produce a seedling that is much higher in resistance. While both parents of LAVENDER FEATHERS show moderate resistance, neither show resistance of the level of this offspring.

The percentages in the list below are for the level of spores on the underside of the basal leaves of a clump. Typically rust lesions and spores are most apparent on the undersides of the basal leaves, but some will show rust lesions and spores on the tops of leaves and even on new emerging leaves. Any rust spores on the surface of the leaves or on new growth would lower the score, based upon the level of coverage on those areas.
As one example of a category, I have seen some very susceptible plants with greater than 75% coverage of spores so that they literally look like orange velvet with almost no green leaf visible. Of course, in these cases, the visible leaf yellows also, so there is technically no "green" areas visible, but there may be some leaf areas not covered in lesions. This system is an average that I do visually, so the only absolute category is the ‘very high’ category, which literally means ‘no visible rust spores on any leaves’. This system, while general, has worked well for my purposes and I continued to use it throughout my screening program. Generally speaking, I consider the categories A+, A and B to be ‘resistant’, while I consider the categories C and D to be ‘susceptible’.

Daylily Rust Resistance Rating System
Lesion coverage
Very high
No visible susceptibility
1% - 25%
26% - 50%
51% - 75%
Very low
Very high

Once first-frost arrived, I culled a great many susceptible cultivars, only retaining those susceptible plants that had multiple other exceptional qualities. One important aspect of screening for resistance in plants is to ensure that there is enough disease for testing. Without adequate exposure to rust spores, false negatives will occur. (False negatives are when a plant appears to show higher resistance than it actually possesses, usually due to a lack of exposure to the pathogen or environmental conditions that reduce the level of infection). 


For that reason I have always maintained susceptible cultivars. I have made a great effort to only maintain otherwise exceptional plants that show rust susceptibility, multiplying them into many clumps to ensure a heavy spore exposure. Susceptible plants must be maintained within a resistance breeding program, even if they are not used in breeding. Because of space concerns, I chose to only maintain susceptible plants if they were exceptional for other traits and of use in my breeding program.

SUBSTANTIAL HEART is one of my 2018 introductions from ENDLESS HEART x SUBSTANTIAL EVIDENCE that showed Very High resistance (A+) throughout all five years of my screening program. The flower also shows excellent rain resistance and sunfastness. 

During the 2012 rust episode, my garden was arranged as any hobby garden typically would be, with no particular planting arrangement design to maximize spore exposure. During the winter of 2012/2013, I pored over the published literature on plant breeding and corresponded with several professional researchers in order to develop a planting scheme that would allow a relatively accurate view of resistance over both time and space and help to eliminate false negatives. In spring of 2013 I divided the selected susceptible plants and began to make a planting arrangement to maximize spore exposure and divided apparently-resistant plants to make multiple random plantings to reduce false negatives.
For the remainder of the program, this was the yearly process:

-New plants added in spring from gardens with rust. 

-Spring division of both select susceptible and apparently-resistant plants increasing clump numbers of both. 

-Once rust appeared, work to spread rust to susceptible plants. 

-Weekly evaluation of susceptibility/resistance. 

-After first frost, cull unwanted susceptible seedlings and cultivars from the program. 
This continued through to fall 2016, completing five years of selection for both resistance and breeding value for resistance. In the context of my program, breeding value for rust resistance means the ability of a given plant to pass its resistance to a higher-than-average number of its seedlings. It is my hope to now send seedlings to warm humid climates where they can be tested in conditions with heavy rust in unsprayed gardens. Because rust appeared one year after the first year I hybridized, I was able to test seedlings for resistance (and their parents for resistance breeding value) through each year of the screening program.
In 2013, the paper Identification of Pathotypes in the Daylily Rust Pathogen Puccinia hemerocallidis (Buck, James W.) demonstrated the existence of multiple races of daylily rust. By bringing in multiple plants from multiple gardens, I was trying to increase the chances of exposing my plants to a variety of these races to strengthen the testing. 

SUBSTANTIAL GLOW is one of my 2018 introductions. A full sibling to SUBSTANTIAL RETURNS and SUBSTANTIAL SUBSTANCE, this one also showed Very High Resistance (A+) throughout the five years of screening. All three of these have been exceptionally good breeders for rust resistance, producing a high percentage of Very High resistance seedlings. All three also show rebloom and through rebloom in some of their seedlings. When bred to other reblooming plants, the percentage of reblooming seedlings is quite high. The flowers of all three are also flat, of strong substance and shine across the garden.

Variable reaction to rust in any given cultivar may reflect environmental differences or varying susceptibility/resistance to different races of daylily rust. The focus of my work was to identify the tiny handful of plants amongst those I was testing that showed the highest resistance over the entire screening program and also showed the highest percentage of equally resistant seedlings that also held their resistance levels over the entirety of the program. Those cultivars and seedlings would become the basis for much of my breeding program.
While I could say much more about those years of screening, the scope of this article does not allow that detail, so I will proceed to list a few of the plants that I found to show high or very high resistance and to also have good breeding value for resistance. There are both tetraploids and diploids in this list.

Highly Rust Resistant Daylilies included in Study
Click on name for information page for most cultivars.
Hemerocallis fulva ex Korea
Seoul National University, NA 54920 Rating: A+
unregistered species
‘Ancient Elf’ (Gossard, 2007) Rating: A+
‘Heavenly Shooting Stars’ (Gossard, 2006) Rating: A+
‘Insider Trading’ (Buntyn, 2003) Rating: A+
‘Bill Fall’ (Sellers, 1994) Rating: A+
‘Chicago Apache’ (Marsh-Klehm, 1981) Rating: A+
‘Mama’s Cherry Pie’ (Shooter-F., 1998) Rating: A+
‘Whooperee’ (Gates-L., 1986) Rating: A+
‘Spider Man’ (Durio, 1982) Rating: A+
‘Notify Ground Crew’ (Hanson-C., 2000) Rating: A
‘Rose F. Kennedy’ (Doorakian, 2007) Rating: A+
‘Kanai Sensei’ (Huben, 2006) Rating: A+
‘Early and Often’ (Huben, 2001) Rating: A+
‘Stella de Oro’ (Jablonski, 1975) Rating: A
‘Kindly Light’ (Bechtold, 1950) Rating: A+
‘Linda’ (Stout, 1936) Rating: A+
‘Mardi Gras Parade’ (Kroll, 1992) Rating: A+
‘Zelazny’ (Michaels, 2004) Rating: A+
‘Heavenly Angel Ice’ (Gossard, 2004) Rating: A+
‘Frans Hals’ (Flory, 1955) Rating: A
‘Pack Hunter’ (Mahieu, 2003) Rating: A
‘Endless Heart’ (Apps-Blew, 2004) Rating: A+
‘Banned in Boston’ (Simpson-D., 1994) Rating: A+
‘Jocelyn’s Oddity’ (Rose, 1998) Rating: A

*For a longer list of resistant cultivars, see the article 

My experience suggests that in my collection of cultivars there are more diploids with resistance than there are tetraploids. I suspect the most useful resistance will be found amongst those plants that are consistently resistant in many gardens over many years. Such plants may represent a combination of multiple resistance genes, or simply one or few genes with broad resistance to many races of rust. It must be remembered that the rust pathogen will continue to evolve and so no resistance can be assumed to be permanent. In time resistance can fail as new rust races emerge although in some cases resistance can be quite durable. However, when a given plant that has previously shown resistance to a race of rust shows susceptibility to another race, that plant genome should not be eliminated, but can be incorporated into lines with resistance to the other race to create broader resistance. I have been very satisfied with the progress I made with breeding for daylily rust resistance.

EARLY SYMPHONY is one of my 2018 introductions from a very complex combination of reblooming lines. It showed Very High rust resistance (A+) throughout all five years of my screening program. A beautiful flower with a deep green throat that holds up will in sun and rain, it is an excellent rebloomer here in my garden. It also throws a high percentage of rust resistant seedlings and rebloom, as well as passing the intense green throat.

An Outline of Suggestions for a Resistance Breeding Program

There are certain ideas and practices that I consider to be of the utmost importance when implementing a rust resistance breeding program.

-All plants to be screened for resistance must not be sprayed with fungicides.

-Arrange plants to create maximum exposure to rust spores.

-Randomly plant clumps of any clone throughout the garden, as environmental influences can skew results creating false negatives.
-Replication reduces false negatives: replication should be with multiple clumps in multiple locations over multiple years.

-In a home garden, make sure that one or more highly susceptible plants are immediately beside the plant to be tested.

-Planting systems for seedlings can vary, but there should be an effort to make maximum exposure to the disease.

-I prefer to start exposure of seedlings as early as possible, and repeat evaluation rating as often as possible. However, I do not rely solely on seedling rating.

-Selected seedlings can be moved into regular plantings to continue testing. I have personally found screening for five years to be very effective in judging long-range and broad-based resistance in my garden, while also allowing time to test for breeding value.

-It is important to remember there are several races of rust. Variations in resistance from garden to garden may represent different races of rust. It is always possible that resistance may fail at some point, as new rust mutations occur. 

-There are likely to be many genes for resistance in daylilies. 
Intentionally combining many resistance genes in one individual is called gene pyramiding, which can combine many genes to create broader resistance to multiple races.

-In my experience, the most effective breeding to produce high resistance is to cross the most resistant plants with each other. There are instances where important traits, such as plant traits or flower traits, may occur on susceptible plants. In these instances, outcrosses of resistant plants to susceptible plants may be made. I refer to such crosses as ‘salvage crosses’. 

-If resistance is not observed in the F1 of a salvage cross, sibling crossing or backcrossing to parents may be required to bring out the desired trait(s) with resistance. This is often a difficult project, usually requiring large numbers of seedlings to find the plant(s) that show resistance combined with the desired trait(s) from the susceptible plant.

This list is not a comprehensive overview of resistance breeding, but is only an overview to present basic and important concepts. (1)

*For a more extensive discussion of breeding and selecting for rust resistance, see my Rust Resistance Articles Page.
Also see the listing of links at the end of this article.

Looking Forward


To move forward we need cooperation, both from professional researchers and from hobbyists. The identification of the most resistant individuals with the greatest breeding value is essential. Those individuals considered 'exceptional' for both their apparent resistance and their breeding value should be made the central focus of university/industry research and trials, as well as hobbyist breeding efforts.


The most effective rust screening will be done in warm humid climates where rust is endemic, winters are too mild to kill the fungus and rust spores are present through much of the year. Those in cold-winter climates may contribute observations when rust occurs, but without winter fungus survival, these cold-winter climate gardens are at a disadvantage due to lack of endemic rust. Cold-winter climate growers may make more strides in breeding for rust resistance when greenhouses are used and rust can be maintained throughout much of the year.
Without laboratory testing to identify resistance genes and which races of rust these genes effect, hobbyists must rely on field testing to progress in their programs. I would strongly encourage researchers to lab-test individual daylilies that have been identified to have very high resistance and very high breeding value in an attempt to identify the genes responsible for this resistance and the races of rust the resistance works for.

An upcoming spring 2019 introduction. This is another wonderful seedling that has shown exceptional, Very High rust resistance (A+) throughout my entire screening program and is an excellent breeder for the trait. The flower is very orchid-like and it is very fertile both ways. Over the next few years, I will be introducing many of the plants that showed the very best rust resistance, along with breeding value for rust resistance, with good plant traits, appealing and durable flowers, and good fertility through my five-year screening program

I will gladly correspond with any researchers who are interested in such cultivars, and would be happy to provide biological samples or plants for research. I would also be willing to make crosses to provide seeds for further research, where such would be helpful. I hope to continue distributing the observations I have made, and work with hobbyists and researchers who have an interest in researching and/or breeding for rust resistance in Hemerocallis.

In Closing

The possibility of breeding lines of daylilies for resistance to rust should be given serious consideration. This is not a new concept, and has been part of plant husbandry and science for over a century. Growers in warm-winter climates have the greatest opportunity to pursue this work of selecting and breeding due to their access to rust throughout much of the year. Those of us in cold-winter climates can also contribute by offering our observations when we do have rust in our gardens and by being aware of and supportive of warm-winter garden efforts toward breeding for resistance.
 (1) Suggested Reading


(For terminology used in this article, please see)


-Plants, Genes and Agriculture - Maarten J. Chrispeels and David E. Sadava; Jones and Bartlett Publishers, 1994.

-Plant Breeding for Pest and Disease Resistance - G.E. Russell; Butterworths Publisher, 1978.