Abutilon theophrasti: Wild Host For Three Fungal Parasites of Soybean

Abstract

Three pathogens, Phomopsis sojae (Diaporthe phaseolorum var. sojae), Colletotrichum dematium var. truncata and C. gloeosporioides (Glomerella cingulata), of soybean [Glycine max] were isolated from velvetleaf [A. theophrasti], a common weed in soybean fields. Lethal stem canker induced by P. sojae developed in 1-2% of velvetleaf plants examined in Champaign County [Illinois, USA] and the pathogen was recovered from 25-65% of the stem sections when plants were .gtoreq. 4 wk old. Recoveries of C. gloeosporioides and C. dematium var. truncata ranged from 0-35% and 0-85%, respectively. Inoculation of ''Amsoy 71'' soybean seedlings with C. gloeosporioides induced leaf cupping and veinal necrosis on expanding leaves. Velvetleaf isolates of C. dematium var. truncata and P. sojae usually were more virulent on soybean pods than were soybean isolates. Isolates of C. gloeosporioides from soybean and velvetleaf were avirulent on soybean pods. Inoculation of soybean pods with Colletotrichum spp. reduced P. sojae in seed. Velvetleaf isolates of C. dematium var. truncata and P. sojae had greater growth rate than soybean isolates on soybean pod and seed extract agar and all isolates regardless of host source grew more rapidly on velvetleaf stem extract agar.