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United States Department of Agriculture

Agricultural Research Service

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Location: Crop Germplasm Research

2012 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:
During the life of this project, a genetic diversity study of 232 C. sublineolum isolates was conducted using a molecular marker technique called AFLP-ABI fingerprinting. A set of representative isolates (20 isolates) was obtained, and each isolate was inoculated on a set of differentially resistant sorghum lines to determine their virulence patterns. Seventeen new pathotypes were established. In order to screen large quantities of accessions for anthracnose resistance reliably, a colonized grain inoculation procedure and a rating system for mass evaluation of sorghum germplasm was developed. Using this method, sorghum accessions from China, Ethiopia, Mali, Mozambique, and Sudan collections were evaluated to identify potential sources of anthracnose resistance, and a number of accessions were found to be highly resistant. Cooperative work also resulted in the mapping of Cg1, a gene for resistance to anthracnose in sorghum. Research to develop an efficient and effective inoculation procedure for the head smut pathogen, Sporisorium reilianum, evaluated four different inoculation methods and found that a single hypodermic injection of 18- to 20-day-old sorghum plants with spore suspension was superior to a method that mimics natural field inoculation. Using this single hypodermic injection method, the research team evaluated 32 isolates of the head smut pathogen collected from different locations in Texas and found two new pathotypes of Sporisorium reilianum. This is the first characterization of the head smut pathogen in the past 40 years in the U.S. Sorghum accessions from Chad and Uganda were evaluated in Mexico and the U.S. for resistance to Peronosclerospora sorghi, the causal agent of sorghum downy mildew. The work identified a number of accessions with high levels of resistance to the sorghum downy mildew pathotypes that exists in Texas and in Mexico. Assessments were made of the vulnerability of elite sorghum lines and hybrids from the U.S. to Sporisorium ehrenbergii Vanky, causal agent of long smut. The work established that promising sorghum cultivars and parental lines released/registered in the U.S. in recent years exhibited varied levels of susceptibility. The long smut inoculation technique developed by this work (which is already being used in Africa) can be used for future mass screening of sorghum for resistance to the disease. Experiments were conducted to evaluate sorghum germplasm from China for resistance against Claviceps africana, causal agent of ergot. Only one accession (PI511832) exhibited some level of resistance to this disease. This work indicated that further screening of sorghum germplasm will be needed to identify accessions that have a high level of ergot resistance in order to minimize the impact of the disease in the U.S. This project expired in FY 2012, but was replaced by 6202-22000-030-00D which is expanding upon the work of the expired project.

4. Accomplishments
1. Molecular markers for distinguishing sorghum head smut races. Sorghum head smut is a significant constraint to productivity and profitability of the crop in many areas due to continuous use of susceptible lines/hybrids, and also variation within the pathogen population. ARS scientists at College Station, Texas, working with scientists at Texas A&M University, used modern molecular tools to assess the genetic diversity of 32 head smut isolates collected from different locations in Texas. Thirty of these tools (known as AFLP markers) were useful in distinguishing among the different head smut isolates. New, virulent head smut races were identified. The new information about the race status will greatly facilitate work by sorghum breeders and other researchers to identify/develop new head smut-resistant sorghums for use by farmers in those regions where smut is a significant obstacle to production.

2. New anthracnose, downy mildew, grain mold, and long smut resistant sorghum. Sorghum is an important grain crop used for human food and animal feedstuffs in many parts of the world. Sorghum diseases cause annual economic losses in yield and seed quality amounting to tens, if not hundreds, of millions of dollars. The most appropriate solution to major sorghum disease issues would be development of new disease-resistant sorghum varieties. ARS scientists at College Station, Texas, working with colleagues in Puerto Rico, Senegal, and Mexico, intensively studied a number of sorghum lines drawn from various sources, with focus on identifying resistance to anthracnose, downy mildew, grain mold, and long smut. The work established that a number of these lines are 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.

Review Publications
Prom, L.K., Egilla, J. 2011. Effect of chitinase and thaumatin on mycelial growth of five sorghum [Sorghum bicolor (L.) Moench] grain molding fungi under in vitro conditions. Journal of Tropical Agriculture. 49(1-2):88-90.

Prom, L.K., Erpelding, J.E., Isakeit, T., Perumal, R., Cuevas, H.E. 2012. Response of sorghum accessions from four African countries against Colletotrichum sublineolum, causal agent of sorghum anthracnose. American Journal of Plant Sciences. 3(1):125-129.

Last Modified: 2/23/2016
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