Soybean Seed Discoloration and Cracking in Response to Low Temperatures during Early Reproductive Growth

Abstract

Prevalence of low temperatures during the flowering adversely affects appearance and quality of soybean [Glycine max (L.) Merr.] seeds at maturity. Our objective was to describe the nature of damage and factors influencing seed quality in a sensitive soybean cv. Kitakomachi and examine genotypic variation in tolerance to discoloration and cracking. The damage was most evident in plants exposed to 15°C (day/night) for 2 to 3 wk commencing from anthesis or 1 wk thereafter. Kitakomachi was sensitive to both discoloration and cracking, whereas Tokei 795 and Tokei 782 were tolerant to discoloratoin and cracking, respectively. Discoloration was first seen when seeds were about 70 to 80% of maximum size. Qualitative histochemical tests indicated a greater presence of phenolics in the palisade layer of the discolored seet coat. Cracking was confined to the upper layers of the seed coat and was associated with damage to osteosclereids. More damage to parenchyma in the funiculus and to osteosclereids in the seed coat was noticed in sensitive genotypes following exposure to cold stress. Within a pair of isolines differing in nodulation, the nodulating line showed more damage than the non‐nodulating line. Additional N fertilization showed varied effects on discoloration depending on duration of chilling and genetpe, but it increased cracking. In contrast, excess soil water status incresed discoloration. Further improvements in crop tolerance and agronomic practise are necessary to produce quality soybeans in cool climates.