Screening for Chilling‐Tolerant Soybeans at the Flowering Stage Using a Seed Yield‐ and Maturity‐Based Evaluation Method

ABSTRACTCold weather damages soybean [Glycine max (L.) Merr.] crops in high‐latitude countries. The decreased seed yields caused by low temperatures are attributed to three main factors: poor growth during the early growth stage, abscission of flowers and pods at the flowering stage, and insufficient grain filling at the pod‐filling stage. The abscission of flowers and pods is the most important factor that contributes to reduced yields. There are differences in chilling tolerance among cultivars developed in Japan at the flowering stage. This study screened for chilling‐tolerant (CT) soybeans developed in high‐latitude countries, such as Canada, Switzerland, Poland, and the Czech Republic. For the screening, plants were subjected to a 28‐d chilling‐temperature treatment after flowering in a phytotron, and six CT cultivars, ‘Maple Arrow’, ‘AC Proteus’, ‘Ceresia, Pelvoux’, ‘Silvia’, and ‘Mazowia’, were found by focusing on seed yield and maturity. These six CT cultivars matured earlier and had greater yields than Japanese cultivars in the field under severe chilling conditions. Moreover, we developed five breeding lines derived from a cross of the CT cultivars Mazowia and ‘Toyoharuka’ (TH). All five breeding lines matured earlier than TH and had yields similar to that of TH in the field under normal conditions. Phytotron tests revealed that the chilling tolerance levels of two of the breeding lines were slightly greater than that of TH. The six CT cultivars found in this study will be useful for chilling tolerance breeding.