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Identification of QTLs associated with horizontal resistance in soybean against Phytophthora sojae with an efficient hydroponic system

Maxime de Ronne: Université Laval

<div>Although the deployment of resistance genes that confer complete immunity against <em>Phytophthora sojae </em>is currently the most attractive means to reduce soybean losses, the constant evolution of new pathotypes can eventually lead to a breakdown in resistance. A complementary approach is to rely on horizontal resistance, or partial resistance, that is not dependent on a gene-for-gene interaction. The objective of this study is to identify QTLs in a soybean population that have been obtained from an early maturing line adapted to Canadian conditions, and a line showing high levels of horizontal resistance both in field observations and greenhouse testing. Altogether, 150 F5 lines that were advanced by mass multiplication in the field without selection except for natural selection were used for the study. All 150 lines were phenotyped exhaustively for horizontal resistance against <em>P. sojae</em> using a hydroponic bioassay allowing direct inoculation of the roots with zoospores. In parallel, all lines were genotyped using a GBS approach and the resulting reads (~1M/line) were used for SNP calling and construction of a genetic map. The association between phenotypic and genotypic data revealed the presence of strong and consistent QTLs for partial resistance of soybean against <em>P. sojae</em>. These results should offer new tools to breeders to combine early maturity and <em>P. sojae</em> resistance into early maturing germplasm adapted for the expanding soybean production in Canada.</div>