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ARS Home » Midwest Area » West Lafayette, Indiana » Crop Production and Pest Control Research » Research » Publications at this Location » Publication #192418
Title: VIRULENCE IN PHYTOPHTHORA SOJAE ISOLATES TO SOYBEANS WITH RPS8 RESISTANCE

Author
item SMITH, D - PURDUE UNIVERSITY
item Abney, Thomas
item SHANNON, J - UNIVERSITY OF MISSOURI

Submitted to: Southern Soybean Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 2/16/2006
Publication Date: 3/8/2006
Citation: Smith, D.A., Abney, T.S., Shannon, J.G. Virulence in phytophthora sojae isolates to soybeans with Rps8 resistance. Southern Soybean Conference Proceedings. 33:6.

Interpretive Summary:

Technical Abstract: Phytophthora root rot, caused by PHYTOPHTHORA SOJAE, is a serious yield-limiting disease in most soybean production regions of the U.S. Major emphasis for the control of this disease has been directed toward the use of Rps1-c, Rps1-k, and/or Rps3-a resistance genes until the recent identification of Rps8. It was initially suggested that Rps8 provided resistance to all P. SOJAE races, but ongoing research in the north central soybean production region of the U.S. evaluating P. SOJAE isolates suggests that more specific information documenting Rps8 virulence is needed. This information is needed to assess the potential threat of P. SOJAE to soybean production and to facilitate management of the disease. Soil was collected from soybean fields with a history of Phytophthora root rot in central Indiana and southwest Missouri in 2005. 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. Additional isolates of P. SOJAE maintained by Abney from IN, KY, MO, and MS were also selected and re-evaluated for virulence on the differential cultivars including Rps8. The predominant race among the isolates of P. SOJAE evaluated was race 1, but there were distinct differences in prevalence of races from the southern compared to the northern locations. Races 1, 2, 13, 15, 17, 24, and 26 were commonly found among the isolates from the southern locations; whereas, races 1, 3, 4, 7, 13, 25, and 28 were common to central and northern Indiana. At least one isolate of races identified as1, 3, 7, and 25 based on the standard set of Rps-differentials was virulent on Rps8; and, more alarming is the awareness that almost all isolates designated as race 15, 17, 24, or 26 were highly virulent on soybeans with the Rps8 gene. Thus, more isolates must be evaluated to expand our knowledge of the effectiveness of Rps8 in management of P. SOJAE in the northern and southern soybean production regions. The data reported in this study continue to document the necessity of using multiple genes to effectively manage P. SOJAE.