Genetic analysis of new sources of soybean resistance to brown stem rot

Brown stem rot (BSR) of soybean [Glycine max (L.) Merr.], caused by Phialophora gregata (Allington & D.W. Chamb.) W. Gams 1971, is an economically important disease prevalent in soybean producing regions of the north-central United States and Canada. To date, all BSR resistant genes identified are located on chromosome 16 (formerly molecular linkage group J). The objective of this study was to determine if four plant introductions from south-central China identified as BSR resistant have resistance genes mapping to the same location on chromosome 16 as previously mapped BSR resistance genes. The four plant introductions, PI 594637, PI 594638B, PI 594650A, and PI 594858B, were crossed to the BSR-susceptible cultivar 'Century 84' to develop four F2 populations. Each segregating population and the parental lines were screened for BSR resistance in growth chamber conditions. The F_2:3 individual plants of each population were tested with the simple sequence repeat (SSR) markers Satt431 or Satt547, which map closely to BSR resistance quantitative trait loci (QTL) on chromosome 16. Associations between molecular data and phenotypic data used to validate QTL were analyzed using single factor ANOVA. Three of the four populations had markers on chromosome 16 significantly associated with BSR resistance with R2 values from 24 to 48%. However, when marker Satt547 was regressed on BSR resistance in population PI 594637 × Century 84, no significant association was observed. This result suggests that PI 594637 could have a new BSR resistance gene. Transgressive segregation also was observed in this population, and highly BSR resistant progeny could be used in the development of BSR resistant cultivars. Additional research and testing in this population will be conducted to identify resistance QTL(s) from this source.