Optimum harvesting time of the black-seeded soybean “Tambaguro” for Edamame (Green soybean) “Murasakizukin 2” by appearance of pods

In order to elucidate the optimum harvesting time of the black seeded soybean “Tanbaguro” for new edamame (green soybean) “Murasakizukin 2”, we examined the changes in the thickness and appearance of pods during the seed growth in 2007 –2009. A significant linear relationship was found between pod thickness and the days or accumulated mean air temperature after flowering. The analysis of covariance revealed that the slope of the regression line did not significantly vary with the year. The percentage of pods with more than 11 mm in thickness reached 70% when the accumulated temperature after flowering exceeded 1250ºC in the mid-June-sowing cultivation (conventional sowing) in all three years. The commercial value of green soybean is lost by appearance of yellow pods, and it occurred when the accumulated temperature after flowering exceeded 1380ºC. These results suggested that the optimum harvesting time of “Murasakizukin 2” could be estimated by the accumulated temperature after flowering. In addition, the tendency of increasing pod thickness at the uppermost four nodes of the main stem was similar to that in the whole plant. Therefore, the pod swelling in the whole plant could be grouped by that at the uppermost four nodes.