Monday, November 13, 2006

Response of Soybean Isolines Differing in Phytophthora Root Rot Resistance to Field Flooding.

James Shannon1, Ryan W. Eddy2, Jeong D. Lee2, Calvin Shumway3, T. S. Abney4, and David Smith5. (1) Univ. of Missouri, PO Box 160, Portageville, MO 63873, (2) Univ of Missouri, Delta Center, P O Box 160 147 State Highway T, Portageville, MO 63873, (3) Arkansas State Univ., College of Agric. ASU, PO Box 1080, State University, AR 72467, (4) USDA-ARS and Dept. Botany & Plant Pathology, Purdue Univ, 915 W. State St., West Lafayette, IN 47907, (5) Purdue Univ, Lilly Hall, 915 W. State St, W. Lafayette, IN 47906

Phytophthora root rot (PRR) and flooding in soybeans is often a problem on heavy clays or poorly drained soils.  Phytophthora root rot (PRR) resistance could decrease losses due to flooding. Alleles for PRR resistance in soybean have been found at eight loci with some loci having more than one allele. Yields of Williams (rps), susceptible to PRR, and 13 Williams isolines differing in alleles for resistance were compared on Sharkey clay under severe flooding and under normal irrigation. Flooding reduced yield 667 kg/ha for Williams rps versus no flooding. Yields were also reduced for Williams Rps1a, rps2, Rps3a, Rps4, Rps5, Rps6, and Rps7. On the other hand, Williams with the genes Rps1k and Rps3b yielded the same or more under flooding compared to non-flood treatments showing that PRR resistance genes can protect soybeans growing under conditions of excess water. Combinations of PRR alleles at  different loci could provide even greater benefit.  More than 50 races of Phytophthora sojae cause PRR, and different resistance genes protect against specific races.  Thus, the effectiveness of PRR resistance genes under conditions of excess water will likely depend on races of the pathogen present in the field.  However, because other factors are obviously involved, PRR resistance will not entirely eliminate soybean losses due to flooding.