Fungal taxonomy / Taxonomie fongique Isolates of Diaporthe–Phomopsis from weeds and their effect on soybean

Greenhouse and laboratory studies were conducted to determine the identity and pathogenicity of Diaporthe– Phomopsis species complex recovered from eight weed species. The identifications of the eight isolates representing four taxa, including two apparently undescribed species of Phomopsis, were based on colony features in pure culture, morphology of alpha or beta-conidia, and internal transcribed spacer sequences. Of the eight isolates, Phomopsis sp. A. from Eclipta prostrata (eclipta), Phomopsis longicolla isolates from both Ipomoea lacunosa (pitted morning-glory) and Chamaesyce nutans (nodding spurge), and Diaporthe phaseolorum from Desmanthus illinoensis (Illinois bundle-flower) caused significant levels of infection on soybean hypocotyls, pods, and seeds. These four isolates from weed species also caused systemic infection of seed similar to the soybean isolate of P. longicolla. Diaporthe phaseolorum isolated from Caperonia palustris (Texasweed) and Aster exilis (slender aster), Phomopsis sp. B. from Sida spinosa (prickly sida), and Phomopsis sp. A from Polygonum aviculare (prostrate knotweed) were not pathogenic to soybean. This is the first demonstration that Phomopsis sp. A, P. longicolla, and D. phaseolorum isolated from eclipta, pitted morningglory, nodding spurge, and Illinois bundle-flower cause seed infection of soybean.