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Managing Karnal Bunt of Wheat

Rush, Charlie
Texas A&M University
Start date
End date
  1. Define Karnal bunt (KB) ecology and epidemiology to enable global deregulation of KB and minimize pathogen spread.
  2. Develop high yielding KB resistant germplasm adapted for the Great Plains region in cooperation with CIMMYT.
  3. Evaluate alternative crops and cattle grazing management systems and develop economic decision aids in minimize the impact of KB.
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NON-TECHNICAL SUMMARY: Tilletia indica, the fungus that causes Karnal Bunt, is a quarantined pathogen. Although its impact on crop yield and quality is extremely minor, its quarantine status is causing economic hardship to wheat farmers and the US wheat industry. The purpose of this project is to conduct research that will provide regulatory agencies with data needed to develop a pest risk assessment, a prerequisite to deregulation. A second aspect is to develop alternative cropping systems and resistant cultivars that will provide producers with management options.

APPROACH: Objective 1. Define Karnal bunt (KB) ecology and epidemiology to enable global deregulation of KB and minimize pathogen spread. Better methods for quantifying T. indica from soil and plant samples are needed. Real time PCR techniques will be developed for this need because of the sensitivity of the method and its ability, not only to detect the pathogen, but also to quantify inoculum density in the soil, teliospores from seed washes (necessary for issuing a phytosanitary certificate for seed sales to other states), and fungal biomass in plant tissue. This technology should have multiple uses in the study of this pathogen. A new research area will be development of a web based real time risk assessment model for KB. Disease risk models are currently available, but their resolution is only at the county level. We want to modify current methods to provide higher resolution, approximately 2 square miles, and in a format that is readily available to producers and wheat related industries that have an interest in disease occurrence. The plant pathology group in Amarillo will work on identifying the major factors that should be included in the disease model and Dr. Srinivasan, head of the Spatial Sciences Laboratory in College Station, will work on development of the web based delivery system. This project should lead to improved disease forecasting capabilities and give producers information needed to make more informed management decisions.

Objective 2. Develop high yielding KB resistant germplasm adapted for the Great Plains region in cooperation with CIMMYT. The wheat breeding programs at KSU, OSU, and TAMU have made single and three-parent crosses with KB resistant material from India and CIMMYT. F2 and F3 generations of these populations are now being grown and we will begin to derive lines this season. Currently all KB resistance screening will have to be done at CIMMYT, PAU, or using real-time PCR in a quarantine laboratory. Our primary focus will be to develop KB resistant hard winter wheat varieties suitable for the Great Plains, but we will also make some crosses targeting other regions. The first, second, and third target priorities of TAMU will be Texas, Colorado, and the hard spring wheat region.

Objective 3. Evaluate alternative crops and cattle grazing management systems and develop economic decision aids to minimize the impact of KB. Cool-season alternative crops research trial will be initiated in the fall of 2004 in Olney, TX (Young County), one of the counties impacted by the Karnal Bunt regulation. Stand establishment, forage, and grain yields will be measured for each cool-season forage crop. Additionally agronomists and animal scientists at Amarillo are collaborating to compare stocker cattle performance on barley, wheat, and triticale and animal performance on summer annuals. New sorghum varieties, higher quality forage sorghums, and other drought tolerant crops will be evaluated in 2004 at locations in the Rolling and High Plains of Texas.

PROGRESS: 2004/04 TO 2007/09
OUTPUTS: Significant progress was made in the KB project during 2007. Three specific areas of research were addressed, i.e., epidemiology, alternative forages, and breeding. Epidemiology: A study was conducted to determine the effect of weather factors on incidence of the disease since its first detection in Texas. Weather variables (temperature and rainfall amount and frequency) were collected and used as predictors in discriminant analysis for classifying bunt-positive and negative fields using incidence data for 1997, and 2000 to 2003 in San Saba County. Rainfall amount and frequency were obtained from radar (Doppler radar) measurements. The three weather variables correctly classified 100% of the cases into bunt positive- or negative fields during the specific period overlapping the stage of wheat susceptibility (boot to soft dough) in the region. A linear discriminant-function model then was developed for use in classification of new weather variables into the bunt-incidence groups (+ or -). The model was evaluated using weather data for 2004 to 2006 for San Saba area (central Texas), and 2001 and 2002 for Olney area (north-central Texas). The model correctly predicted bunt incidence in all cases except for the year 2004. The model was also evaluated for site-specific prediction of the disease using radar rainfall data and in most cases provided similar results as the general level evaluation. The humid thermal index (HTI) model (widely used for assessing risk of Karnal bunt) agreed with our model in all cases in the general level evaluation, including the year 2004 for the San Saba area, except for the Olney area where it incorrectly predicted weather conditions in 2001 as unfavorable. Alternative Forages: Research trials were initiated to evaluate cool-season forage species thought to provide adequate forage potential.In the fall of 2006, numerous varieties of annual forage including oats, barley, rye, ryegrass, and forage legumes were evaluated for forage yield potential against both SRW wheat and HRW wheat. Plots were harvested with a flail harvester in early April and percent moisture was determined by pulling sub-samples from each plot. Similar to previous years, the non-host crops for KB were viable options for producers in the Rolling Plains of Texas. Oats, barley, and rye all performed comparably to wheat and triticale. Breeding: The breeding team continues to make crosses with known sources of KB resistance, and advance material from the segregating populations. The program currently has F2 through F5 populations that are segregating for KB resistance. We now have F4 populations with W485/HD29. Selections will be made for leaf rust and stripe rust resistance this season and the resulting head-rows will be evaluated in 2009. Work with TX01M5009 (Mason/Jagger//Pecos) is continuing and has shown consistent resistance to KB. It will be proposed for germplasm release in 2009. In addition, a closely related line TX03M1096 (Mason/Jagger) has been tested for 2 years in the Southern Regional Performance Nursery (SRPN) and 3 years in state-wide Texas trials. It will be proposed for a hard red winter wheat cultivar release in 2008.
PARTICIPANTS: Charlie Rush, Jackie Rush and Gaylon Morgan were the project leaders in this project. USDA APHIS was supportive of the Epidemiological Studies as was the USDA-ARS, through which funding was received through a KB Federal Initiative.
TARGET AUDIENCES: The primary target audience for this work has been those policy makers who have responsibilities for deregulating Karnal Bunt in the USA. Information concerning resistant germplasm will be of benefit to commercial breeders and of interest to Texas farmers from the regulated areas.

IMPACT: 2004/04 TO 2007/09
The KB risk assessment model that was developed is highly accurate and specific to wheat production areas in Texas. It has potential to be used in spray advisory programs in regulated wheat fields or could be used by producers in making disease management decisions. The work was presented at the annual meeting of the American Phytopathology Society and was submitted for publication in Plant Disease. Cool-season forages continue to be a very important component of the agricultural industry in the Rolling Plains and Concho Valley of Texas. It is highly likely that wheat will continue to be a major component of any cool-season forage program, but this research has shown that barley, triticale, and oats are all very economically viable options for winter forage in these areas of the state. Additionally, alternative uses of wheat, silage or hay, appear to be viable options based on the results of 2007 research. Another alternative to wheat pasture is the use of annual forage sorghums for grazing and/or silage production. With the current demand and infrastructure being established, it is highly likely that biomass crops and biodiesel crops will become more important in the previously KB affected counties. Based on yield trials with similar climatic conditions, canola, rape, and other mustards are a good potential fit for the KB areas. However, no specific data is currently available for these cool-season bio-fuel crops. The research on these bio-fuel crops will begin in the 2007-08 season. The most significant highlight from the breeding effort is development of TX03M1096. This line has not been officially released by AgriLife Research, but plans are for an early 2008 release. This will be the first hard red winter wheat cultivar bred specifically for Texas that has KB resistance.

Funding Source
Nat'l. Inst. of Food and Agriculture
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Sanitation and Quality Standards
Bacterial Pathogens
Grains, Beans, Legumes