Abstract
Generally soybean is a crop with a very high autogamy rate, but the allogamy rate may increase when the low temperature before the flowering stage induces abnormal pollen formation. In this study, we examined the effects of a low temperature before the flowering stage on the natural out-crossing rate. The cotyledons of soybean cv. Aomarukun are green, but those of the F1 obtained by crossing with cultivars with yellow cotyledons are yellow. Therefore, this was used for judgment of crossing. The plants of Aomarukun were grown in a growth chamber at 8-15°C for 7 days before the flowering stage, and then they were placed adjacent to the pollen parent under field conditions and the out-crossing rate was investigated. As a result, the out-crossing rate was 0-0.18% in the control plants and 0.1-0.62% in the low temperature-treated plants, indicating that the low temperature before the flowering stage enhances the rate considerably. In addition, the effect of the setting of beehives of honey bee, which is one of the pollinators, was examined. The crossing rate was higher in the plot with beehives(0.21%)than in the plot without beehives(0.07%). Thus, it was confirmed that a low temperature before the flowering stage is a factor increasing the natural out-crossing rate.
