Disease Phenotyping

Determining the Reaction of Wheat Lines to Important Diseases

Diseases have traditionally been a major limiting factor in the production of wheat in Kansas. Estimated losses from all diseases averaged about 16% from 1976 through 1988 (3). That is equivalent to about 160 million dollars each year. As a result, wheat breeders have recently increased their concentration on developing varieties with resistance to important diseases. For example, prior to 1977, wheat varieties were resistant to only one disease when they were released. In contrast, varieties released from 1988 through the present have been resistant to about eight different diseases (3). Clearly, there has been a dramatic increase in the effort to develop varieties with improved levels of resistance.

To produce a new wheat variety takes about 12 years from the time that initial crosses of parents are made until its release to wheat producers. Therefore, at any given time, breeding programs have many wheat populations at different stages of development. During the development time, populations are reduced from thousands of individuals to the one individual with the desired properties that make it an improvement over current commercial cultivars.

Obviously, the wheat breeder is the focal point of the effort to produce new varieties; however, many other professionals also contribute. Wheat pathologists are members of that group because part of the selection process is determining the reaction of those breeding lines to important diseases (disease phenotyping). This can help the breeders eliminate susceptible lines from the population and advance resistant ones.

Another area where disease phenotyping is important is with informing the wheat producers about the reaction of current commercial cultivars to diseases of importance in Kansas. The producers use this information as they select which varieties to plant. There are two main KSU Extension publications that contain this information: Kansas Performance Tests with Winter Wheat Varieties (11) and Wheat Variety Disease and Insect Ratings (8). The reactions of 29 or 69 varieties, respectively, to 12 different diseases are contained in those publications. Because varieties come and go over time and new races of pathogens develop, updating the publications on an annual basis is a necessity. To provide current, accurate data to producers requires constant disease phenotyping of current commercial cultivars.


Rationale and Significance:

Planting resistant varieties is arguably the best control method for plant diseases. Such a practice is relatively inexpensive and "environmentally friendly." Annual savings to wheat producers in Kansas from planting resistant varieties is about $58 million (3). Obviously, it is important to continue to develop resistant cultivars to maintain and improve on this success story. A main component of this development is expertise provided by wheat pathologists.

The importance of disease phenotyping will not diminish in the future. Over the past few years, biotechnology has received much coverage in the press and is an exciting area within agricultural research. One area in the biotech arena that appears especially promising to the breeding effort is the use of "marker assisted selection" (MAS) to follow traits of interest. The use of these genetic markers to determine if a certain gene is present in a plant (genotyping) can speed up the breeding process. Some markers of interest are those linked to disease resistance genes. Therefore, a breeder can quickly tell if a certain wheat line contains a resistance gene without having to go through the laborious process of having the line inoculated and evaluated. However, this technique does not eliminate the need to disease phenotype wheat lines. There are many cases where MAS may show that a gene is present in a line but the gene may be silenced, masked by other genes, or just not effective in the variety where it is located. In other words, even using MAS, lines still have to occasionally be phenotyped for reaction to disease to confirm that the gene is active and giving the proper level of protection. The bottom line is that determination of the reaction of wheat lines to diseases, by using traditional techniques, will continue to be important in the future and is a necessary partner to marker assisted selection.

In the past, state and federal sources have provided the primary funding for the wheat pathology effort to the breeding and extension programs. However, declining funds from those sources and inflation have significantly reduced their relative contribution. Disease phenotyping research cannot continue with the current level of state and federal support. Therefore, to maintain the needed level of pathology commitment to the breeding and extension efforts, additional sources of funding must be sought. This proposal seeks funds from the Kansas Wheat Commission for partial support of a Research Assistant for the disease phenotyping component of the wheat pathology lab.

Related Current/Previous Research:

There are approximately 20 different wheat diseases that may be found in Kansas (3). Of those, only 14 cause enough loss to warrant control methods including the development of resistant varieties. Wheat phenotyping for three of the diseases (leaf rust, stem rust, and stripe rust) is handled by the USDA/ARS at KSU. Similarly, phenotyping for wheat streak mosaic is accomplished by faculty members at the Hays Experiment Station. Expertise to evaluate wheat lines for eight of the remaining 10 diseases is in the wheat pathology lab in Manhattan. In fact, accurate methods to evaluate four of this latter group have been developed by that lab and include Wheat Soilborne Mosaic (5), tan spot (10,12), take-all (9), and barley yellow dwarf (2,6, recently-completed research funded by the Kansas Wheat Commission). Additionally, the unit has adopted and refined methods published by others to phenotype wheat for four other diseases; Stagonospora leaf blotch (7), Septoria leaf blotch (7), Cephalosporium sripe (1), and Fusarium head blight (scab) (4). The wheat pathology lab at KSU is unique in the entire country by possessing expertise to test wheat for reaction to so many different diseases. That makes it a valuable resource for the breeding and extension efforts that should be maintained.

Procedures/Methodology:

Objectives:

1. Establish and maintain field evaluation nurseries for important wheat diseases.

2. Phenotype wheat lines in the greenhouse for reaction to wheat diseases.

Progress Report

Results: Field areas were prepared during the summer and nine field experiments have been planted. Two were planted in mid-September at a site that routinely has moderate to severe pressure from barley yellow dwarf (BYD). The first experiment includes 42 cultivars and breeding lines and the second includes 10 common commercial cultivars. The goal of the first experiment is to determine the disease reaction of commercial cultivars and to continue to identify breeding material from around the world that has useful levels of resistance to BYD. The second experiment involves a split-plot design (healthy and diseased) with large plots to allow for more accurate yield-loss determinations. Results from this experiment will be disseminated to wheat producers in KSU Extension publications to help them make informed decisions as to which cultivars to plant. Seven additional field experiments were planted in early October to test various lines for reaction to tan spot and Fusarium head blight (scab). The goal of the third and fourth experiments is to determine whether virus-induced transposons can affect the reaction of wheat to tan spot and scab, respectively as a tool to select resistant lines out of susceptible cultivars. The fifth experiment is the Northern Winter Wheat Regional Scab Nursery of 60 breeding lines from northeastern and northcentral states. The sixth experiment involves evaluation of reaction to scab of breeding material (48 entries) from the wheat breeding programs of the central Great Plains states of Kansas, Nebraska, and South Dakota. The seventh experiment involves evaluation of the reaction to scab of the Kansas Intrastate Nursery (KIN) of advanced breeding lines (48 entries) from both KSU wheat breeders. The eighth experiment contains breeding populations of Dr. Fritz as he attempts to enhance the level of scab resistance in his breeding program. The ninth experiment involves lines developed by Dr. Bai as he enhances our ability to use Marker Assisted Selection (MAS) to select for resistance to Fusarium Head Blight. Finally, inoculum has been produced to infest a 1-acre field area where Dr. Fritz will select breeding lines for reaction to important foliar pathogens such as tan spot, Septoria leaf blotch, and Stagonospora leaf blotch.

Significance of the results: Disease evaluation nurseries for barley yellow dwarf, Fusarium head blight, tan spot, Septoria leaf blotch, and Stagonospora leaf blotch will be established each year. These are the diseases currently occupying a main focus of the Kansas wheat breeding effort where pathology expertise is needed. If evaluations for other diseases are desired, they will also be established. Each disease has its own unique requirements to obtain a good evaluation nursery. In general, procedures involve planting numerous breeding lines in appropriate-sized plots that are to be inoculated. In some experiments, adjacent plots are also planted and maintained disease free. At the appropriate time, nurseries are inoculated with the desired pathogen and a conducive environment (e.g. mist irrigation) provided to ensure the development of an epidemic. At the proper growth stage, the lines are visually evaluated for reaction to the disease, statistical analyses performed, and data given to the breeders and extension specialists. Breeders will use these data to decide which lines to advance and identify resistant lines to be used as parents for future breeding populations. Extension specialists will disseminate data concerning commercial cultivars to wheat producers.

NEXT STEPS: The field experiments will be maintained (weed control, fertilizer, etc) throughout the year and, where appropriate, inoculated with the appropriate pathogen. Disease evaluations (phenotyping) will be performed, analyzed, and results disseminated to breeders and wheat producers. During the fall, winter, and spring, numerous greenhouse experiments will be conducted to phenotype important cultivars and breeding lines to diseases including scab, tan spot, Septoria leaf blotch, and Stagonospora leaf blotch.