1995 Volume 61 Issue 4 Pages 362-368
Soybean leaves artificially inoculated with basidiospores of Thanatephorus cucumeris (AG-2-3 of Rhizoctonia solani) developed at first, primary lesions, then, secondary lesions and eventually, irregular large-sized lesions. The germ tubes of the germinating basidiospores formed appressoria and their infection pegs penetrated into the epidermal cells. A stroma-like structure was produced within the invaded tissues. Hyphae growing radially from this structure formed circular necrotic spots (≤1mm diam.) which corresponded to the primary lesions. After further incubation in a moist chamber, hyphae from the primary lesions continued to grow on the leaf surface and hyphal tips re-entered the leaves through the stomata, causing secondary lesions with circular to irregularly shaped areas of necrosis around the primary lesions. The large-sized irregular lesions developed from additional hyphal infection through stomata. Many fruiting hymenia of the pathogen were detected on the stems of winter wheat or soybean, especially in fields where soybean was intercropped with winter wheat. The severity of the soybean foliar blight lesions caused by basidiospores increased with the delay in wheat harvest or with the increase of the soybean planting density.
