2010 Annual Report
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.
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.
Fungi pathogenic to important agricultural crops in the U.S. were obtained, cultured, and characterized. New strains from China and from California were characterized by morphology and DNA sequencing, and compared with domestic pathogens from forages, alfalfa, tree fruit, and vegetable crops. Fungi included strains and species in the genera Alternaria, Stemphylium, and Ulocladium, and three new species were described. A key to species and descriptions of species in the genus Ulocladum was produced. Molecular markers were identified that enabled distinctions between strains within a species. Specific DNA analyses sequencing methods revealed new species, new lineages within families, and new host associations among these fungi. Further analyses at the sub-species level of strains in the genera Stemphylium and Ulocladium contributed to understanding the evolutionary basis for biological species, pathogenicity and host specificity.
The effects of four levels of elevated atmospheric carbon dioxide on the quantity and quality of spores produced by fungi growing on timothy hay were studied. Leaf carbon-to-nitrogen ratio was positively correlated with the quantity of A. alternata spores produced per gram of leaf, and spore production was increased nearly three-fold at the higher levels of carbon dioxide. Rising levels of carbon dioxide often increase the biomass and carbon-to-nitrogen ratio of plant leaves. This research demonstrates that leaf changes induced even at moderately increased carbon dioxide levels greatly enhance the sporulation of forage grass fungi, as well as the common allergenic species A. alternata.
The research addresses National Program 205 Rangeland, Pasture and Forages, Component II: Plant Resources a) Lack of Available Germplasm and c) Overcoming Limitations to Plant Growth and Cevelopment); Component III: Forage Management (a) Forage Establishment and Persistance. Project Objectives are also relevant to National Program 303, Plant Diseases, Component I: Disease Diagnostics, Detection, Identification and Characterization of Plant Pathogens a) New Diagnostic Methods and Tools and b) Detection, Characterization, and Classification of Pathogens; and Component III Plant Disease Resistance b) Disease Resistance in New Germplasm and Varieties.
Wolf, J.E., Oneill, N.R., Rogers, C.A., Muilenberg, M.L., Ziska, L.H. 2010. Elevated atmospheric carbon dioxide concentrations amplify Alternaria alternata sporulation and total antigen production. Environmental Health Perspectives. 118(9):1223-1228.
Wang, Y., Pei, Y., Oneill, N.R., Zhang, X. 2010. Ulocladium cantlous sp. nov. isolated from Northwest China: morphology and molecular phylogenetic position. Mycologia. 102(2):374-383.
Wang, Y., Fu, H., Oneill, N.R., Zhang, X. 2009. Two new species of Stemphylium from Northwest China. Mycological Progress. 8(4):301-304.