Variation in Morphological, Cultural, and Pathological Characteristics ofPhialophora gregataandAcremoniumsp. Recovered from Soybean in Wisconsin

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Abstract
Isolates of Phialophora gregata recovered from soybean stems were classified into two pathotypes based on their ability (type I) or inability (type II) to cause chlorosis, necrosis, and wilt of foliage. Both pathotypes caused a similar degree of internal stem discoloration, but type I isolates caused a greater amount of plant height reduction. Type I isolates constituted 72% of all P. gregata isolates evaluated for pathogenicity. Acremonium was isolated at a lower at a lower frequency than P. gregata. Acremonium isolates caused low to moderate degrees of vascular and pith discoloration but caused no foliar symptoms and only a slight reduction in plant height. Maximum growth rate was measured at 20 and 24-28.degree. C for P. gregata and Acremonium, respectively. Isolates of P. gregata, unlike Acremonium, did not sporulate on acidified potato-dextrose agar but did sporulate on green bean agar. Electrophoretic studies revealed isozyme differences between P. gregata and Acremonium, Fusarium oxysporum and Verticillium dahiae were not isolated from field-grown soybean plants that showed vascular discoloration or foliar symptoms.