Seed Coat Cracking in a Soybean Cultivar “Satonohohoemi” and Effects of Planting Time on Its Occurrence: Norikazu Nakayama, Ryo Yamamoto, Tatsuo Hosono and Satoshi Ohno

Seed coat cracking appearing in a soybean cultivar “Satonohohoemi” was investigated for 3 years in relation to planting time and environmental conditions during the seed-filling period. Two types of cracked seeds, one with irregular cracks that accounted for a major part of the cracked seeds and the other with line-shaped cracks, were observed. Late planting in mid-June significantly reduced the occurrence of both types of cracking but its effect on irregular cracks was much larger than that on line-shaped cracks. No significant correlation was detected between the occurrence of irregular cracks and 100-seed weight during the 3-year experiment, which suggests that factor(s) other than seed size may be involved as a major factor in reducing irregular cracks by late planting. Since the flowering date rather than planting date was highly correlated with the occurrence of irregular cracks, the effect of late planting on the occurrence of irregular cracks may arise through delaying flowering time. Therefore, flowering time can be a practical indicator to predict the occurrence of irregular cracks in the cultivar. In addition, the number of days and accumulated temperature during the seed-filling period also showed a relatively high correlation with the occurrence of irregular cracks. Line-shaped cracks exhibited a significant, positive correlation with solar radiation during seed-filling and a higher correlation with planting date than with flowering date. Irregular and line-shaped cracks may be caused by different physiological mechanisms.