Evaluation of soybean resistance to Sclerotinia sclerotiorum at different phenological stages and over different periods of exposure to inoculum

Evaluation of soybean resistance to Sclerotinia sclerotiorum at different phenological stages and over different periods of exposure to inoculum The objectives of this work were to determine the most adequate phenological stage of soybean plants for inoculation of Sclerotinia sclerotiorum and the period of contact between inoculum and plant tissues to detect partial resistance of soybean to the pathogen. Plants of two soybean cultivars, MG/BR-46 (Conquista) and M-SOY 8200 were inoculated at five different phenological stages (V-1, V-2, V-3, V-4 and R-1). Inoculation involved different periods of contact between culture disks of an isolate of S. sclerotiorum which was selected based on high aggressiveness against soybean. It was observed that disease severity decreased as plants became older and it was concluded that V-1 and V-2 (leaves and stems) and V-3 (leaves) were ideal stages for inoculation during tests aimed at determining levels of resistance in soybean cultivars. Continuous contact of inoculum with plant tissues yielded good results for inoculation of S. sclerotiorum, either onto detached organs or onto organs connected to living plants. Ninety genotypes of soybean were evaluated by placing culture disks in continuous contact with folioles. Only 19 genotypes were moderately resistant and, among these, only two were moderately resistant in inoculation involving whole plants.