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CROP BREEDING & GENETICS

Inheritance and Genetic Mapping of Resistance to Pythium Damping-Off Caused by Pythium aphanidermatum in ‘Archer’ Soybean

^a Dep. of Plant Pathology, 217 Plant Sciences Bldg., Univ. of Arkansas, Fayetteville, AR 72701
^b Dep. of Crop, Soil and Environmental Sciences, 115 Plant Sciences Bldg., Univ. of Arkansas, Fayetteville, AR 72701

^* Corresponding author (jrupe{at}uark.edu).

Pythium damping-off and root rot of soybean [Glycine max (L.) Merr.] causes poor stands and consequently reduces yields. Resistance to seedling diseases caused by Pythium spp. was reported in the soybean cultivar Archer and was described to be associated with the Rps1k gene for resistance to Phytophthora sojae. To characterize the inheritance of Pythium damping-off resistance in Archer and to determine if this resistance is linked to Rps1k, the cross of Archer x ‘Hutcheson’ (susceptible parent) was made and F_2:4 lines generated. Parents and F_2:4 lines were screened with Pythium aphanidermatum using a hypocotyl inoculation technique. Five days after inoculation, plant survival was scored. The F_2:4 lines and parents were also inoculated with race 7 of P. sojae to assess the association of resistance to Pythium spp. with the Rps1k gene. Data from the F_2:4 lines fit the model for a single dominant gene in Archer that confers resistance to P. aphanidermatum. The genetic linkage test showed that resistance to P. aphanidermatum was independent of the Rps1k gene in Archer. To identify the genomic location of the Pythium resistance gene, F_2:4 lines were screened with simple sequence repeat (SSR) markers from all the soybean molecular linkage groups (MLGs). Two SSR markers, Satt510 and Satt114 on MLG F, which were polymorphic between the parents and the resistant and susceptible bulks, were shown to be associated with Pythium resistance. The Pythium resistance gene, named Rpa1, was located 10.6 cM from Satt510 and 26.6 cM from Satt114.

Abbreviations: BSA, bulk segregant analysis • HS, hyphal swelling • MLG, molecular linkage group • PCR, polymerase chain reaction • QTL, quantitative trait locus • R, resistant • S, susceptible • SSR, simple sequence repeat