2012 Annual Report
1a.Objectives (from AD-416):
Enhancement of sorghum productivity by identifying lines with multiple disease resistance genes, understanding the mechanisms of resistance, and characterizing new and emerging fungal pathogens are the primary objectives of this project. Over the next 5 years we will focus on the following objectives.
Objective 1: Identify and characterize the pathotypes of Colletotrichum sublineolum (anthracnose) and evaluate sorghum germplasm for resistance. Subobjective 1.A. Identify pathotypes of C. sublineolum in the U.S. and Puerto Rico.
Subobjective 1.B. Identify new sources of resistance to anthracnose within adapted and exotic sorghum germplasm collections.
Objective 2: Determine the inheritance and allelic relationships of host plant resistance to diverse pathotypes of anthracnose.
Objective 3: Characterize diverse sorghum germplasm for resistance to grain mold and downy mildew to facilitate the breeding of resistant lines.
Subobjective 3.A. Identify sources of resistance to grain mold.
Subobjective 3.B. Identify new sources of resistance to pathotype 6 (P6) of Peronosclerspora sorghi, causing sorghum downy mildew.
1b.Approach (from AD-416):
1) Two hundred thirty-five single spore isolates of C. sublineolum collected from Texas, Arkansas, Georgia, and Puerto Rico are being maintained on dried colonized Whatman No. 2 filter paper and stored in the laboratory. For identifying the pathotypes C. sublineolum, isolates will be selected based on similarity coefficient values from the molecular diversity analysis and from recent isolate collections (permits will be obtained from APHIS to move anthracnose-infected leaves from locations outside of Texas) for virulence analysis on 18 sorghum differentials (SC326-6, SC414-12E, BTX378, TAM428, TX2536, SC328C, QL3, BTX398, SC283, BRANDES, SC112-14, THEIS, BTX623, SC748-5, PI570841, PI570726, PI569979, and IS18760). Seeds of the differentials will be grown in pots containing Metro-Mix 200 potting medium, and placed in the greenhouse at 25 degrees C. To identify new anthracnose-resistant sources, the sorghum association panel, mini-core from India, near-isogenic lines for brown midrib from Nebraska, parental lines, and accessions from the U.S. Sorghum collection mainly from African countries (Algeria, Egypt, Gambia, Ghana, Senegal, Swaziland, and Zaire) will be evaluated in various locations in Texas and Puerto Rico.
2) Crosses will be generated between resistant sources PI569979, PI570726, BTx378, IS18760, and RTx2536, and the susceptible parent PI609251. To study the gene action, F2 populations (400 plants per cross) will be planted in greenhouses, along with the parents. Pathotypes of C. sublineolum [Pathotypes 24 (College Station); 25 (Arkansas); 33 (Puerto Rico); and 35 (Georgia)] will be used for inoculations.
3) Sorghum germplasm as in the anthracnose study, including SC719-11E, Tx2911 (resistant controls) and RTx2536 (susceptible control), will be evaluated in Texas and Puerto Rico to identify grain mold resistant sources. In this study, a randomized complete block design, split-plot arrangement will be used, with cultivars as main plots and treatment as sub-plots. Treatments will be (a) Alternaria spp., (b) mixture of Alternaria spp. F. thapsinum (CS121) and C. lunata (LP09-1), and (c) water-sprayed control.
4) To identify resistant sources to the new pathotype (P6) of Peronosclerospora sorghi, causal agent of downy mildew, sorghum accessions, including the susceptible check Pioneer hybrid 84G62, will be evaluated in fields known to have a history of high incidence of P6. Sorghum germplasm will be planted in a randomized complete block design and each accession will be replicated three times. Also, greenhouse screening will be conducted during the winter months using the sandwich inoculation method.
This is a new project that replaced 6202-22000-027-00D and which is expanding upon the work of the precursor project. In work by this project in FY 2012, the inheritance pattern of second generation plants from five sorghum crosses against a specific pathotype (AMP 182) of the anthracnose pathogen, Colletotrichum sublineolum, was established. Preliminary examination of the data has shown that a single dominant gene in sorghum controls its resistance to anthracnose. Other work in FY 2012 involved cooperative efforts with other scientists from ARS, academia, West Africa, and Mexico to evaluate more than 400 sorghum accessions chosen from the U.S. Sorghum Association Panel, converted sorghum lines, commercial hybrids, and exotic germplasm from Senegal for resistance to anthracnose, leaf spot, grain mold, and long smut. Several promising lines were identified that possess significant resistance to one or more of these important sorghum diseases. These lines may be useful in sorghum enhancement programs in the U.S. and other parts of the world.
New races of the sorghum anthracnose pathogen. Due to the hyper-variable nature of the anthracnose pathogen, there is a continual need to monitor the pathogenic population from different geographic regions in order to breed for stable resistance. ARS scientists at College Station, Texas, working with scientists at Texas A&M University, detected 17 new races of the anthracnose pathogen from 20 isolates collected from the U.S. and Puerto Rico. Documentation of these new anthracnose races is important to breeders in their efforts to develop new, disease-resistant sorghum cultivars, and also to support ongoing efforts to manage these diseases through conventional disease control approaches.