Association of soybean seed traits with physical properties of natto

Breeding of soybean [Glycine max (L,) Merr.] cultivars suitable for natto involves selection for seed traits that influence the quality of the product. The objectives of this study were to evaluate the relationship of 11 seed traits to six natto quality traits and to assess the influence of genotypes and environment on the traits. Sixteen small-seeded genotypes were grown in replicated tests at three Iowa locations during 2 yr. The natto traits evaluated for each plot were wafer absorption, water loss, hardness of steamed seeds and natto, and darkness of steamed seeds and natto. Seed traits were total sugar, free sugar, sucrose, raffinose, stachyose, protein, oil, fiber, protein + oil, protein + oil + fiber, and seed size. There were significant differences among genotypes during one or both years for all the traits, except fiber content. Significant differences between years or among locations were observed for all traits, except water loss after steaming and stachyose content. None of the seed traits was significantly correlated with darkness of the steamed seeds or natto, All of the seed traits, except stachyose, oil, and seed size, were significantly correlated with one or more of the other natto quality traits. Protein + oil was significantly correlated with natto quality and other seed traits and can be a useful selection criterion in breeding cultivars for the natto industry.