Oomycetes species associated with soybean in Buenos Aires Province (Argentina)

Soybean damping off and root and stem rot are mainly caused by soil oomycetes and they can cause severe seedling stand reductions. Between 2013 and 2016, soybean production areas were surveyed in different localities of the north (NBA) and southeast (SEBA) of Buenos Aires Province. Plant, soil and post harvested grain samples were obtained, brought to the laboratory and treated by multiple techniques. The isolates recovered were identified using both morphological and molecular characters. As regards seedlings and soil, 68 Phytophthora isolates were recovered from NBA and 124 from SEBA, all of which were classified as Ph. sojae. Also 181 Pythium isolates were recovered from NBA and 102 from SEBA, belonging to nine Pythium species and three Phytophytium species; and four Pythium species respectively. In both cases P. ultimum and P. irregulare were prevalent. With respect to grain samples, a total of 40 Pythium isolates were recovered, belonging to seven species of Pythium and one species of Phytopythium. The species most frequently recovered were Phy. vexans and P. acanthicum. Pathogenicity was evaluated with representative isolates of each of the 21 species on soybean cv. Harosoy. P. ultimum sensu lato, P. irregulare, P. sylvaticum, P. aphanidermatum and P. paroecandrum were highly pathogenic on soybean seedlings, whereas P. acanthicun, P. nunn and P. periplocum were non-pathogenic on soybean seedlings. This study provides a comparative characterization of oomycete species associated with soybean and provides a basis for disease management and breeding programs in Argentina.