Submitted to: Southern Soybean Conference Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 9/10/1997
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Phytophthora root rot (PR), caused by Phytophthora sojae, is not a serious problem in Kentucky, but occasionally soybeans develop economic levels of the disease. Prior to this work, specific information document PR distribution or races of P. sojae in Kentucky was not available. This information was needed to assess the status of P. sojae as a potential threat to soybean production and to aid in management of the disease where necessary. Soil was collected from 23 fields representing nine major soybean-producing counties in Kentucky during the summer of 1994. In fields with plants exhibiting PR, soil adjacent to diseased plants was collected. Other soil samples were collected at random from fields both with and without a history of PR. Isolates of P. sojae were obtained from the soil samples using a soybean seedling bioassay. Race determinations were based on differential virulence following hypocotyl inoculation of soybeans with different Rps genes. Fifty-seven isolates of P. sojae were harvested from 13 of 23 fields and from all counties from which soil was collected. Eight of the 13 fields yielding isolates had no prior history of PR. The predominate race of P. sojae isolates was race 1; this race was present in soil from 11 of 13 fields and eight of the nine counties yielding P. sojae isolates. Other races found were 2, 13, 15, 24, 26, and an unidentified race. Six of 13 fields yielded multiple races of P. sojae. Results indicate that P. sojae is common in Kentucky agricultural soils, and the race composition is more similar to that reported in southern soybean production regions than in the Midwest. Apparently host resistance and/or other unknown factors limit the occurrence of PR in most fields and most years.