Searching for New Sources of Resistance to Brown Stem Rot in Soybean.

Brown stem rot (BSR) of soybean, caused by Phialophora gregata, is an economically important disease prevalent in soybean producing regions of the north-central U.S. and Canada. To date, all BSR resistant genes have been found on molecular linkage group (MLG) J, known to contain several soybean disease resistance genes. Identification of new sources of resistance to this disease is important to growers and breeding programs developing BSR-resistant cultivars. The objective of the study was to determine if several plant introductions (PI) carry BSR resistant genes previously identified on MLG J. Four PIs identified as resistant to BSR, PI 594637, PI 594638B, PI 594650A, PI 594858B were crossed to the BSR-susceptible cultivar Century 84 to develop four F2 populations, LDx03-47-2, LDx03-48-2, LDx03-49-1, and LDx03-50-3. One hundred fifty five F2 individuals from each segregating population and the parental lines were screened for BSR resistance in growth chamber conditions in a complete randomized block design with three replications. F2 populations were tested with the SSR markers Satt431 and Satt547, which map closely to the MLG J QTL. In three of the four populations, markers in MLG J were significantly associated with BSR resistance, with R2 ranging from 0.5to 0.7. However, when marker Satt547 was regressed on colonization data in population LDx03-47-2, the R2 was very low (0.008). The results could be indicative of a new source of BSR resistance. Additional testing in this population, however, will be necessary to confirm this finding.