Damping‐off of soybean in southern Brazil can be associated with different species of Globisporangium spp. and Pythium spp.

Abstract Damping‐off of soybean is a common problem in some fields in southern Brazil. Frequently, Phytophthora sojae has been pointed out as the main causal agent. However, questions were raised as to whether other oomycetes could also be present. Hence, the objectives of this study were to isolate, identify, and determine the pathogenicity and aggressiveness of oomycetes isolated from soybean seedlings. Thirty‐three isolates were obtained from 13 fields. Isolates were identified based on morphology and molecular methods. Nine species were recovered: Pythium conidiophorum ( n = 14, 42.4%), Globisporangium rostratifingens ( n = 7, 21.2%), G . irregulare ( n = 2, 6.1%), G . spinosum ( n = 1, 3.0%), G . ultimum var. sporangiiferum ( n = 2, 6.1%), Pythium acanthicum ( n = 2, 6.1%), P . deliense ( n = 1, 3.0%), P . inflatum ( n = 1, 3.0%), and P . torulosum ( n = 3, 9.1%). Pathogenicity and aggressiveness were determined with two soybean cultivars (DM57i52 and NEO530) in a seed rot assay and a root rot assay. All isolates were pathogenic to soybean with variable levels of aggressiveness in both assays. The range of seed disease severity index varied from 7.5 to 100 for DM57i52 and from 23.1 to 100 for NEO530. The mean root disease severity index of the soybean cultivars ranged from 29.4 to 92.8. This is the first official report of G . irregulare , G . rostratifingens , G . spinosum , G . ultimum var. sporangiiferum , P . acanthicum , P . conidiophorum , P . deliense , P . inflatum , and P . torulosum causing damping‐off of soybean in the state of Rio Grande do Sul in southern Brazil.