NC227: Ergot: A New Disease of U.S. Grain Sorghum
Statement of Issues and Justification
Ergot of grain sorghum caused by Claviceps africana is a new and potentially devastating disease emerging in the United States. The ergot epidemic in the Americas began in Brazil in 1995 and by October of 1997 had spread as far north as Nebraska. Very little is known about this pathogen or host-plant traits that might influence the infection cycle. Given this threat to U.S. sorghum production, a cooperative and integrated ergot research effort is needed that incorporates plant pathologists, biologists and geneticists across the Central Great Plains. The project described in this proposal will address this need by focusing on research questions concerning ergot biology and disease management strategies. Research on ergot biology will focus on questions relating to epidemiology, taxonomy, and alternate hosts of the pathogen. Research on disease management will focus on integrated ergot control strategies including cultural practices, chemical application, and host-plant mechanisms that contribute to disease resistance or ergot-avoidance. The development of this committee will help to eliminate unnecessary duplication of effort and will facilitate cooperative exchange of information and ideas.
Justification:
Sorghum (Sorghum bicolor (L) Moench) is the worlds fifth most important cereal crop with over 100 million acres of production each year. Sorghum is also an important feed grain in the U.S., which annually produces over 10 million acres of sorghum. Most of the sorghum production in the U.S. is under dryland conditions in the Central Great Plains. Bennett et al. (1990) in their book, "Modern Grain Sorghum Production," characterize grain sorghum as a "wonder crop" of semi-arid and arid agriculture. They note that production of grain sorghum has been revolutionized in the past 40 years and predicted that grain sorghum acreage will expand in response to the increasing yield potential of the crop.
Claviceps africana is a fungal pathogen that infects unfertilized ovaries (Bandyopadhyay et.al. 1996). Any condition that reduces male fertility of sorghum predisposes the crop to infection by C. africana which is capable of rapid infection and dispersal. There are two Claviceps species that cause ergot of sorghum (Bandyopadhyay et al. 1996). Sorghum ergot was first identified in India in 1917 (C. sorghi) and Kenya (C. africana) in 1924. Sorghum ergot was considered an Old World disease caused by a single species, C. sorghi, until 1991 when the African species was separately described as C. africana (Frederickson and Mantle 1988; Frederickson et al. 1991). C. africana has recently caused an ergot epidemic that has spread through most of the sorghum-producing areas in North and South America, and Australia (Arias-Rivas et al. 1997). The ergot epidemic in the Americas began in Brazil in 1995. By 1996, ergot had spread across most of South American and to Australia. Ergot was identified in Mexico and the Caribbean in February of 1997 and by late March was found in southern Texas. The disease spread through the U.S. during the summer of 1997 and by October had spread as far north as Nebraska. Ergot has become an endemic problem in most sorghum producing areas in the U.S. and the world.
For years ergot has been a problem in Africa and India and it has now become endemic in the U.S. and is a growing problem (Bandyopadhyay et al. 1996). Seed production fields are particularly at risk. The seed parents used to produce hybrid seed are male-sterile, and male- sterility predisposes florets to ergot infection. Intensive fungicide treatment and careful management are required to limit this threat; however, little information is available to determine best management and control strategies. Ergot may also be a problem in grain production fields where intensive management may not be feasible. Cool, wet weather during the flowering period could reduce pollen viability and lead to conditions that are favorable to wide-spread ergot infection (Brooking, I.R. 1979; McLaren and Wehner 1992). The development and use of sorghum hybrids that remain highly fertile under cool, wet conditions would limit this potential problem.
Ergot can be an economically devastating problem. In seed production fields, yield losses ranging between 10 to 80% have been reported in India and annual losses of 10 to 25% were reported in seed production fields in Zimbabwe (Bandyopadhyay et al. 1998). Ergot is not usually a problem in grain production fields, but significant yield losses associated with ergot infection have occurred following cool mid-season conditions in some parts of Australia in 1996 and Mexico in 1998.
Although yield losses associated with ergot infection can be significant, indirect losses may be even more important. Harvesting grain from ergot infected fields can be difficult. Infected florets exude a "honey-like" substance and grain harvesting equipment can be plugged or otherwise fouled by contaminated grain. Ergot contamination reduces grain quality and limits its use as a feed-stock. Feed-refusal of ergot contaminated grain has been reported for poultry and swine. The economic impact of ergot in the United States is difficult to assess at this point. Seed production losses in Brazil were estimated at $US 3 million in 1995 (Bandyopadhyay et al. 1996). Industry reports from Australia suggest that increased management costs associated with the control of ergot in seed production fields may increase seed production costs by $20-25 per bag, a net cost of$4M per annum to the industry (Bandyopadhyay et al. 1998).
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