Location: Crop Germplasm Research2008 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 2008, diversity within a collection of 44 isolates of Sporisorium reilianum (the sorghum head smut pathogen) from different locations in Texas, 3 African isolates (two from Uganda and one from Mali), and 2 maize head smut isolates collected from Mexico was determined using Amplified Fragment Length Polymorphism (AFLP). Selective amplification reactions were performed using primers with one selective nucleotide (EcoRI+A, EcoRI+T, EcoRI+G, EcoRI+C), and all 4 possible primers of MseI+A, MseI+T, MseI+G, MseI+C. This resulted in a total of 16 +1/+1 unique primer combinations. IRD-labeled EcoRI primers were used and the AFLP amplification products were analyzed using a LI-COR-NEN® Model 4300 dual-dye automated DNA Analyzer. The primer combination E-A+M-A showed maximum (56%) and E-T+M-G showed minimum (28%) polymorphism. The mean polymorphism over 16 primer combinations was 42%. Cluster analysis is being performed to determine the similarity matrix of this selected head smut population. More than 200 U.S. converted lines, commercial hybrids, and exotic sorghum germplasm accessions were evaluated in several locations in the U.S. and Mexico for resistance to anthracnose, downy mildew, grain mold, and head smut. In addition, 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) were evaluated for resistance to anthracnose in the greenhouse. (NP 303, Components 2, 3, Problem Statements 2A, 3B)
1. 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 over 2.5 million hectares of land annually; however, sorghum pathogens cause major economic losses in yield and seed quality estimated to be in the 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. Scientists in the Crop Germplasm Research Unit at the Southern Plains Agricultural Research Center, College Station, Texas, in collaboration with ARS scientists at Mayaguez, Puerto Rico, and at Texas A&M University, evaluated hundreds of U.S. converted lines and commercial hybrids, and sorghum accessions from Ethiopia, Mali, Sudan, and Uganda germplasm collections for anthracnose resistance using Colletotrichum sublineolum-colonized grain inoculation methods. The work established that a large number of the accessions were highly resistant to the disease. This accomplishment is important because it will provide 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. (NP 303, Component 3, Problem Statement 3B)
2. Downy Mildew-resistant Sorghum Hybrids: In recent years, a new pathotype (P6) of the sorghum downy mildew pathogen was identified in Wharton County, Texas. As a result, there is need to identify new sources of downy mildew resistance. Scientists in the Crop Germplasm Research Unit at the Southern Plains Agricultural Research Center, College Station, Texas, in collaboration with scientists at Texas A&M University, evaluated 30 grain sorghum hybrids in a field in the downy mildew-infested area for resistance to the new fungal pathotype. The work established that 5 of the 30 hybrids had a high level of resistance (<1% systemic disease incidence); these hybrids exhibited no or few local fungal lesions. This accomplishment is significant because it has identified potential new sources of P6 resistance in sorghum that can be utilized by breeders to develop new hybrids for U.S. farmers that will assure ability to avoid losses to the P6 downy mildew pathogen. (NP 303, Component 3, Problem Statement 3B)
5. Significant Activities that Support Special Target Populations
Prom, L.K., Erpelding, J.E., Montes-Garcia, N. 2008. Evaluation of sorghum germplasm from China against Claviceps africana, causal agent of sorghum ergot. Plant Health Progress (online). doi:10.1094/PHP-2008-0519-01-RS.