Studies on Dactuliochaeta Glycines and the Epidemiology of Red Leaf Blotch of Soybeans

147 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.Red leaf blotch, caused by Dactuliochaeta glycines, of soybeans (Glycine max) was studied in field trials in Zambia, Africa and the causal agent was examined under quarantine conditions in the laboratory at the University of Illinois at Urbana-Champaign (UIUC).Dactuliochaeta, a new genus, was established to accommodate Pyrenochaeta glycines and its synanamorphic state, Dactuliophora glycines. The genus is characterized by setose sclerotia which germinate to form mycelia, then setose pycnidia, and/or pycnidia and sclerotia on sclerotial surfaces. The inner walls of the pycnidia are lined with ampulliform to lageniform, phialidic conidiogenous cells often periclinally thickened at the conidogenous locus.Red leaf blotch reduced yields of four cultivars from 8 to 37% and reduced seed size from 21 to 29%. Number of seeds per plant and per pod was significantly greater in fungicide-sprayed than nonsprayed plots. Disease severity was greatest on leaves at the lowest nodes from early vegetative through reproductive growth stages.Epidemics varying in severity were induced using different levels of fungicide applications. Disease severity regressed on node position decreased significantly from lower to upper nodes. One-thousand seed weight, seed size, and yield increased significantly with one or more applications of fungicide in the 1984-1985 growing season. Regressions of 1000-seed weight, seed size, and yield on the area under the disease progress curve for the median leaf explained 92, 90, and 72% of the variation, respectively.In culture, the fungus produced sclerotia on inoculated leaf disks of soybeans and other leguminous plants, wheat seed and wood, and on various organic nitrogen sources. The LD$\sb{50}$ for sclerotia was between 90 and 120 min at 100 C. The optimum temperature for germination of conidia was 20 and 25 C. Nine Glycine spp. and six leguminous plants were identified as hosts.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD