Location: Crop Germplasm Research2010 Annual Report
1a. Objectives (from AD-416)
The objectives of this project are to: 1) identify and characterize different races of anthracnose (Colletotrichum sublineolum) based on their virulence patterns and by using molecular marker techniques; 2) evaluate sorghum germplasm for resistance to anthracnose; and 3) evaluate germplasm for resistance to grain mold, downy mildew, and head smut diseases.
1b. Approach (from AD-416)
1) Large-scale evaluations of the base collection through screening of the core (2,400 accessions), and the Sudan and Mali working (600 accessions) collections will be carried out. The core collection represents a random selection of the base collection. The Sudan and Mali working collections are accessions that breeders have selected based on agronomic performance and yield potential. Selected resistance sources will be screened over locations in different years to assess their horizontal disease resistance. 2) Two hundred fifty C. sublineolum single spore isolates collected over the past four years from various locations of the United States and Puerto Rico and are currently in long-term storage in the laboratory will be used. Host plant evaluations in the greenhouse will be conducted to establish the pathotypes of C. sublineolum. 3) Two closely related pathotypes of P. sorghi, P1 and P3, will be used to identify the differentially expressed unique sequences using standard AFLP technology as well as SSH. 4) A total of six cultivars, B1, BTx7078 and SC170-6-17 (susceptible lines), BTx635 (resistant line), SC140 and SC64 (their reaction to head smut is unknown), will be included in this study. Four inoculation methods--seed treatment, soil treatment, media placement, and syringe injection--will be employed. Four Texas isolates collected from College Station, Corpus Christi, Weslaco, and Beeville will be evaluated, with three replications for all four inoculation methods and all six cultivars simultaneously. In each replication, disease incidence (i.e., whether the inflorescence is replaced with sori or not) will be recorded.
3. Progress Report
In FY 2010, we tested the virulence pattern of 20 anthracnose isolates on sorghum growing in the greenhouse to identify the different races of the pathogen; several races of the sorghum anthracnose pathogen previously unknown to science were identified. We also tested 32 head smut isolates from Texas and documented two new races that were confined mainly to south Texas. Documentation of these new anthracnose and head smut races are important for breeding new resistance sources and for managing these diseases. Working with cooperators in Puerto Rico, West Africa, Mexico, and at Texas A&M University, we evaluated over 400 lines, including U.S. Sorghum Association Panel lines, converted sorghum lines, commercial hybrids, and exotic germplasm for resistance to anthracnose, downy mildew, grain mold, ergot, long smut, and target leaf spot. The work identified several lines that possess significant resistance to one or more important sorghum diseases, and that therefore may be useful in sorghum development/enhancement programs in the U.S. and other parts of the world. To understand the mechanisms of anthracnose resistance, the project initiated a heritability study by crossing several highly resistant lines with the susceptible line PI609251 to produce first-generation (F1) seeds. The F1 seeds were planted in Isabela, Puerto Rico, to produce second-generation (F2) seeds that will be planted for further analyses in FY 2011.
1. New anthracnose-resistant sorghum. The fungal disease anthracnose annually causes millions of dollars of losses in sorghum in the U.S. ARS researchers at College Station, Texas, and Mayaguez, Puerto Rico, working with scientists at Texas A&M University, tested many sorghum lines from Ethiopia, Mali, Sudan, and Uganda for genetic resistance to anthracnose, and showed that a considerable number of these lines are highly resistant to the disease. The work also showed that variations in weather (frequency/amount of rainfall, and relative humidity) were the most critical factors affecting severity of the disease in sorghum, with higher rainfall and humidity making disease development occur faster and with more intensity. This work has identified important anthracnose-resistant sorghum germplasm that will be utilized by sorghum breeders both in the U.S. and other countries to develop new disease-resistant sorghum varieties that will increase sorghum production efficiency and profitability in the U.S. and in many other areas of the world.
2. Grain mold-resistant sorghum germplasm. Globally, grain mold is the most important disease of sorghum; it seriously reduces both crop yield and grain quality. The sorghum community is in agreement that identifying new grain mold-resistant sorghum germplasm for exploitation by breeders is the most desirable approach to successful management of this disease. ARS researchers at College Station, Texas, working with scientists in Senegal (West Africa) and at Texas A&M University, identified six sorghum lines from West African sources that are highly resistant to grain mold strains that occur in Senegal; some of the lines were also mold resistant in the Texas environment. This work has identified important new grain mold-resistant sorghum germplasm that will be exploited by sorghum breeders to develop new disease-resistant sorghum types for productive utilization by farmers both in the U.S. and in Africa.
3. African sources of target leaf spot-resistant sorghum. Sorghum target leaf spot is a regionally important fungal disease that can, under some circumstances, cause serious sorghum losses in both the U.S. and Mexico. Through analysis of a number of sorghum types collected in Mali, Sudan, and Uganda, ARS researchers at College Station, Texas, working with scientists in Mexico, identified several important new sorghum sources that exhibit high levels of resistance to the fungus that causes target leaf spot. Sorghum breeders now have access to new sorghum germplasm that can be used to develop new commercial sorghums that will circumvent the target leaf spot problem. Such new sorghums will increase production efficiency and profitability in the U.S. and Mexico, and in some other nations as well.
Montes-Garcia, N., Prom, L.K., Isakeit, T. 2009. Effect of temperature and relative humidity on sorghum ergot development in northern Mexico. Australian Journal of Plant Physiology. 38(6):632-637.