Optimum Harvesting Time of the Early Black-seeded Soybean “Tambaguro” for Edamame (Green Soybean) “Kyo Natsuzukin” in Kyoto Prefecture, Judged from the Pods Appearance and Chemical Properties of Boiled Seeds

In order to elucidate the optimum harvesting time of the early black seeded soybean “Tambaguro” for new edamame (green soybean) “Kyo Natsuzukin” (commercial name), we examined the thickness and appearance of pods, and the chemical components of boiled seeds during the seed growth using two cultivars, “Natsudoritambaguro 1” and “Natsudoritambaguro 2”, in Kyoto prefecture in 2010–2013. The average pod thickness in both cultivars reached 11 mm at 51–52 days after flowering in 2010, a high-temperature year, and reached 12 mm at 56–57 days after flowering in 2011, an average-temperature year, but did not increase thereafter. Assuming that the early limit of the harvesting period is the time when the percentage of thinner pods less than 10 mm thick, which is the standard thickness for shipment in Kyoto, reached less than 30%of total pods. This time corresponds to the time when the accumulated temperature after flowering reached 1400 degrees Celsius in both cultivars. Throughout the harvesting period in both cultivars, the color of seed coat changed from light to deep purple, but the content of free sugars and amino acids reached the maximum before the time when the color of whole hilum became pinkish. At this time, the pod thickness reached 10–11 mm, which is slightly thicker than the shipment standard in Kyoto. Therefore the optimum harvesting time judged from the chemical property is earlier than that judged from the pods appearance.