Pythium aphanidermatum has a cosmopolitan distribution in the warmer parts of the world. The aim of this study was to identify the causal agent of damping off in soybean seedlings on late planting dates under hot conditions, from different locations in Buenos Aires province. The isolates induced different levels of plant and seedling death and growth rate at different incubation temperatures (15, 25 and 35°C). In accordance with morphological, cultural and molecular characteristics, the pathogen was identified as P. aphanidermatum, and this is the first report of this oomycete causing soybean root and stem rot in Buenos Aires province, Argentina.

Pythium aphanidermatum presenta una distribución cosmopolita, principalmente en las regiones cálidas del mundo. El objetivo de este trabajo fue identificar el agente causal del damping off en plántulas de soja en fechas de siembra tardía bajo condiciones cálidas, en diferentes localidades de la provincia de Buenos Aires. Los aislamientos indujeron diferentes niveles de mortandad de plantas y plántulas y en la tasa de crecimiento a diferentes temperaturas de incubación (15, 25 and 35°C). De acuerdo con la morfología, las características culturales y moleculares, el patógeno fue identificado como P. aphanidermatum, y esta es la primera cita de este oomycete causando podredumbre de tallos y raíces en soja en la provincia de Buenos Aires, Argentina.

Stem canker caused by Diaporthe phaseolorum var. caulivora is an important disease of soybean in Argentina. The objective of this study was to determine its survival ability in artificially infested straw under laboratory and field conditions. In laboratory, stem pieces of soybean, maize, sorghum, sunflower, potato and wheat were autoclaved, placed in petri dishes on Potato Dextrose Agar and Water Agar, and inoculated with a 7-day-old pathogen culture. All crop residues were colonized and produced perithecia. Debris artificially infested with D. phaseolorum var. caulivora were placed in plastic net bags and transferred to an un-cropped area in a field plot at the University of Buenos Aires. Straws were left on the ground from winter to spring season in both 2007 and 2008 years. After 6 months abundant perithecia were developed in all straws. However, a higher number of perithecia on soybean and sunflower compared to maize, sorghum and potato was determined. These findings suggest that other crops, besides soybean, could maintain alive the inoculum of Diaporthe phaseolorum var. caulivora from soybean for at least 6-7 months.