Submitted to: Soybean Disease Compendium
Publication Type: Book / Chapter
Publication Acceptance Date: 8/10/1999
Publication Date: N/A
Technical Abstract: Brown spot, also known as Septoria leaf spot, was reported in the United States in 1922 and first described in Japan in 1951. Yield losses have ranged from 8 to 15% under natural field infestation and from 8 to 34% in inoculated field plots. Brown spot is primarily a leaf spot disease, although seeds, pods, and stems of maturing plants also are infected. Irregular, dark brown spots varying from minute specks to areas 4 mm in diameter appear on both upper and lower surfaces of unifoliolate leaves. These leaves quickly turn yellow and drop. The brown pycnidia of Septoria glycines (teleomorph Mycosphaerella uspenskajae), the causal organism, form in dead tissues of old lesions. Primary inoculum arises from conidia and mycelium overseasoning on infected leaf and stem debris and in diseased seeds. Sources of resistance in soybean have not been found in over 10,000 accessions screened. However, resistance to the pathotoxin produced by S. glycines has been reported. Some wild species of Glycine appear to be resistant.