2013 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.
In work by this project in FY 2013, second generation plants from two sorghum crosses (RTx2536 x PI609251 and PI570726 x PI609251) were evaluated to determine the pattern of inheritance of resistance to a pathotype (AMP 155) of the anthracnose pathogen, Colletotrichum sublineolum. Examination of the data established that a single dominant gene controlled the resistance in RTx2536 to this pathotype, while the resistance in PI570726 x PI609251 is recessive. Other work in FY 2013 involved cooperative efforts with other scientists from ARS, academia, and West Africa to evaluate more than 400 sorghum accessions chosen from the U.S. Sorghum Association Panel, converted sorghum lines, breeding lines, commercial hybrids, and exotic germplasm from Senegal for resistance to anthracnose, head smut, 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 sorghums resistant to grain mold. Globally, grain mold is the most important sorghum disease. The identification or development of new sorghum types that are resistant to grain mold offer the most promising, environmentally friendly approach to successfully controlling the disease. ARS scientists at College Station, Texas, evaluated 38 sorghum accessions from Ethiopia and Mali, along with resistant and susceptible controls, for resistance against the grain mold fungus, Fusarium thapsinum. Three accessions exhibited lower grain mold severities and higher germination rates when compared with the resistant controls Sureno and SC719. This work is important because it identifies critical new germplasm for use by sorghum breeders in developing new sorghum varieties that will be resistant to one of the world's most important grain molding diseases. New resistant varieties will increase sorghum production efficiency and profitability in the U.S. and in many other areas of the world.
New anthracnose, head smut, and long smut resistant sorghum. Sorghum diseases annually cause economic losses in both yield and seed quality amounting to tens if not hundreds of millions of dollars. The most effective and economical solution to major sorghum disease issues would be development of new disease-resistant sorghum varieties. ARS scientists at College Station, Texas; Lincoln, Nebraska; and Mayaguez, PR, working with collaborators from Texas A&M University and the Centre National de la Recherche Agronomique, Senegal, West Africa, intensively evaluated sorghum lines drawn from a number of sources for their inherent resistance to anthracnose, grain mold, head smut, and long smut. The work established that a number of these lines were highly resistant to one or more of the diseases. This work is a significant advancement in sorghum disease research in that it provides to sorghum breeders and other researchers critical new germplasm that will be foundational in developing new, disease-resistant sorghum varieties for productive use in world agriculture.
Isakeit, T., Collins, D.D., Rooney, W.L., Prom, L.K. 2013. Effect of fungicides on the reaction of sorghum hybrids to anthracnose in Burleson County, Texas, 2012. Plant Disease Management Reports. 7:FC044.
Cuevas, H.E., Prom, L.K. 2013. Assessment of molecular diversity and population structure of the Ethiopian sorghum [Sorghum bicolor L. (Moench)] germplasm collection maintained by the USDA-ARS National Plant Germplasm System using SSR markers. Genetic Resources and Crop Evolution. 60(6):1817-1830.