Location: Crop Germplasm Research2009 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
Anthracnose is a serious fungal disease in sorghum. In FY 2009, the genetic diversity of more than 100 sorghum anthracnose isolates was accomplished using appropriate molecular biology techniques; the ultimate goal is to identify the different races of the sorghum anthracnose pathogen. More than 300 U.S. converted sorghum lines, commercial hybrids, and exotic germplasm accessions were evaluated in several locations in the U.S., Mexico, and Senegal for resistance to anthracnose, downy mildew, grain mold, head smut, long smut, leaf blight, and rust. In addition, a subset of the 245 sorghum lines from India (representing the genetic diversity within the sorghum collection maintained by the International Crops Research Institute for the Semi-arid Tropics) was evaluated for resistance to head smut in the greenhouse. Several promising lines were identified that possess significant resistance to one or more of these important sorghum diseases.
1. Sources of Anthracnose-Resistant Sorghum Germplasm: Sorghum is an important global grain crop used for human food and animal feedstuffs. In the U.S., the crop is grown on more than 5 million acres of land annually; however, sorghum pathogens cause major economic losses in yield and seed quality estimated to be in the multiple millions of dollars each year. New research is needed to monitor and assess emerging races of these pathogens, most notably anthracnose, downy mildew, and head smut. In collaboration with ARS scientists at Mayaguez, Puerto Rico, and with scientists at Texas A&M University, more than 300 converted lines and commercial hybrids, and sorghum accessions from Ethiopia, Mali, Sudan, and Uganda were evaluated for anthracnose resistance using a Colletotrichum sublineolum-colonized grain inoculation method. The work established that a large number of the accessions are highly resistant to the disease. This accomplishment is important because it provides sorghum breeders with critical new germplasm for use in developing fully anthracnose-resistant sorghum varieties that will increase sorghum production efficiency and profitability in the U.S. and in many other areas of the world.
2. Sources of Downy Mildew-Resistant Sorghum Germplasm: In recent years, a new pathotype (P6) of the sorghum downy mildew fungus was identified in southeast Texas; therefore, new sources of downy mildew resistance are needed. In collaboration with scientists at Texas A&M University, 30 grain sorghum hybrids and 40 germplasm accessions from Ethiopia, Mali, Sudan, and Uganda were evaluated for mildew resistance. Seven hybrids and 11 accessions were found to have high levels of downy mildew resistance. This work is significant because it has identified potential new sources of downy mildew resistance in sorghum that can be utilized by breeders to develop new hybrids for U.S. farmers that will not be economically affected by the downy mildew pathogen.
3. Sources of Leaf Blight- and Rust-Resistant Sorghum Germplasm: Sorghum leaf blight and rust are important fungal diseases of sorghum in some sorghum-producing areas of the world. It is therefore important to identify new sorghum germplasm resources that exhibit resistance to damage by these diseases. A number of sorghum germplasm accessions from Mali, Sudan, and Uganda were evaluated for resistance against Exserohilum turcicum, the causal agent of leaf blight; and Puccinia purpurea, the causal agent of rust. Five accessions from Mali, four accessions from Uganda, and one accession from Sudan were highly resistant to leaf blight; two accessions from Mali and one accession from Uganda showed significant resistance to rust infection. This accomplishment is significant because breeders can use these new sources of leaf blight- and rust-resistant sorghums to develop new hybrids that will increase sorghum production efficiency and profitability in both the U.S. and in other nations, particularly Mexico.
Isakett, T., Prom, L.K., Wheeler, M.H., Puckhaber, L.S., Liu, J. 2008. Mycotoxigenic potential of ten Fusarium species grown on sorghum and in vitro. Plant Pathology Journal. 7:183-186.