Abstract
Soybeans with a large interval between central and lateral blooming are considered to be tolerant to cold weather (CW) during the flowering stage. We introduced the lateral blooming (LB) trait into Hokkaido soybeans, and evaluated their CW tolerance. We conducted two crosses between an indeterminate CW tolerant Canadian variety Labrador with the LB trait and determinate Hokkaido varieties without the LB trait. Then we selected determinate lines with and without the LB trait. The selected lines were exposed to the low temperature of 18ºC day/13ºC night for four weeks from the beginning of flowering. The CW tolerance index (CTI) concerning the pod number and seed yield was significantly higher in the lines with the LB trait (LB lines) than in the lines without the LB trait. Similar results were observed at the test field for cold tolerance in a cooler region where the two lines were selected. The CTIs concerning the pod number and seed yield in the two selected lines were significantly higher than those in Toyomusume, and also tended to be higher than or equal to those in Hayahikari. The two lines mentioned above had a larger number of LB nodes than in Toyomusume, and longer total flowering period (about 15 days) than in Toyomusume and Hayahikari (about 10 days). Thus, the introduction of the LB trait into soybeans was suggested to improve CW tolerance in Hokkaido.
