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United States Department of Agriculture

Agricultural Research Service

2011 Annual Report

1a.Objectives (from AD-416)
Objective 1: Establish basic, fundamental genetic structures to identify and characterize fungal populations pathogenic to alfalfa and other forage legume crops. Develop diagnostic tools and phylogenies to aid in the identification of fungal pathogens of alfalfa. Describe new species and lineages based on this information. Apply existing and new methodologies to identify molecular evolutionary genetic relationships within fungal species that integrate morphology, biogeography, and host specificity.

Objective 2: Identify novel sources of resistance to fungi. Evaluate Medicago truncatula and Medicago lines and accessions for disease resistance in order to identify molecular markers associated with resistance. Determine host specificities of closely related pathogenic Stemphylium strains to M. sativa and M. truncatula lines relative to their host of origin.

1b.Approach (from AD-416)
A species and strain phylogeny for fungi causing diseases of alfalfa, specifically Stemphylim and Pleospora, will be developed based on strains from diverse hosts based sequences of multiple loci. The molecular phylogenies will be integrated with data that distinguish morphological characters to enable the production of keys to species. New and existing strains or pathotypes from alfalfa or its associated rotation crops and weed hosts will be characterized and integrated into updated phylogenetic frameworks. Once the molecular and morphological descriptions of new collections are complete, keys to groups of species will be prepared that can be used for the identification of species of Stemphylum and Pleospora. Closely related strains identified as single species groups will be analyzed for further molecular diversity using two approaches: DNA fingerprinting (AFLP), and a new multi-gene approach which will type specific sequences from multiple loci (MLST). Research will be developed to utilize resistant and susceptible M. truncatula lines models for functional genomic studies including research to map and identify resistance genes, determine mechanisms of defense, and investigate host-pathogen relationships. Cultivar selection will be based on the presence and range of highly desirable agronomic traits, including fall dormancy, genetic diversity, winter hardiness, yield, and a variety of growth habits. To determine the vulnerability of alfalfa to Stemphylium strains and species that cause disease in other crops, pathogens of alfalfa will be evaluated for virulence on M. sativa and M. truncatula cultivars selected for high and low susceptibility to leaf spot disease.

3.Progress Report
The scientist on this project retired in the prior fiscal year. Funds were used to support the technician who took care of the cultures of pathogens derived from forage legumes. These cultures were organized and deposited in culture collections where they will be available to future workers.

Review Publications
Pei, Y., Geng, Y., Oneill, N.R., Zhang, X. 2010. Three novel species of Stemphylium from Sinkiang, China: their morphological and molecular characterization. Mycological Progress. 10:163-173.

Last Modified: 7/30/2015
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