New insight into Rps genes and the management of Phytophthora sojae
Abstract
Phytophthora root rot of soybeans causes substantial yield losses across United States’ soybean production regions. This research documents the current race diversity of Phytophthora sojae in Indiana. Soil samples were evaluated for P. sojae from soybean fields throughout Indiana in 2005 and 2006. Races 1, 3, 4, 25, 28, and 33 were predominant races; however, races 7, 8, 9, 12, 17, 19, 26, 29, 32, 41, 43, and 44 were also present. Over 50% of the isolates were virulent on Rps1-a, 1-b, 1-c, 1-k, and 7. Rps3-a, 6 or 8 would provide high levels of P. sojae control in Indiana. The damage caused by Phytophthora was also measured using a menefoxam treatment as a control across isolines containing different Rps genes. Plant stand, plant height, seed weight, and yield were greater in treated plots than in non-treated plots across cultivars. Menefoxam application methods were not significantly different at most locations. A few Isolates from field trial locations and select producers’ fields were virulent on Rps8, the newest resistance gene to date; however, this limited occurrence in Indiana justifies the use of Rps8 resistance. Virulence on Rps8 was found in isolates from Indiana, Kentucky, Missouri, Mississippi and North Carolina; isolates of races 10, 15, 17, 24, and 26 were consistently virulent, whereas virulence was limited or variable within isolates of races 1, 7, 33 and 41. Knowledge of Rps8 virulence is important to soybean breeders for effective utilization of this new resistance gene. The impact of crop management practices (crop rotation, tillage, and Rps gene resistance) on P. sojae populations was evaluated. No-tillage and continuous soybeans had significantly greater prevalence of P. sojae compared to tilled (ridge, chisel, and plow) and cornsoybean rotation. The use of Rps resistance genes reduced inoculum potential. This thesis research also identified P. sojae resistance in soybean germplasm entries that also express Asian soybean rust resistance. In addition to identifying potential for multiple disease resistance, some of the lines appear to have a novel gene or gene combination of high interest for resistance to P. sojae.
Degree
Ph.D.
Advisors
Abney, Purdue University.
Subject Area
Plant Pathology
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