Establishement of Selection Criteria for Breeding Sprout Soybeans.

Soybean sprouts, a traditional vegetable in Asia, are gaining popularity in the U.S. Soybean sprout demand has been supplied by natto cultivars that share some seed characteristics with sprout cultivars, but natto seeds do not meet all requirements of sprouts, causing seed rejection by sprout manufactures. The objective of this study was to establish breeding criteria for development of sprout soybeans. A total of 15 soybean genotypes were evaluated for sprout characteristics including seed-born fungus presence, hypocotyl length, hypocotyl thickness,  percentage of high-, mid- and low- quality sprouts and fresh weight of high-, and mid- quality sprouts, sprout yield, seed size and water absorption rate. ‘MFS-561’, a commercial sprout cultivar, and ‘Glenn’, a commercial cultivar were used as checks. Results showed that six fungi genera, Penicillium sp., Aspergillius sp., Epicoccum sp., Fusarium sp., Alternaria sp. and Mucor sp., widely distributed among genotypes. Hypocotyl length ranged from 12.7 to 16.2 cm, and most genotypes had longer hypocotyl than ‘MFS-561’. All genotypes produced thicker hypocotyl than MFS-561, and more fresh-sprout yield than ‘MFS-561’ except for V12-1764 and ‘Glenn’.  Cracking cotyledons and abnormal seedlings could be considered the two main constraints affecting soybean sprout quality. Correlation coefficient among all traits indicated that water absorption, seed size and hypocotyl thickness were independent variables and may be not needed for sprout selection. We suggested that good sprout characteristics should include high-quality sprout >45%, mid-quality sprout < 34.7%, high-quality sprout fresh weight > 91.2 g, mid-quality sprout fresh weight> 65.1 g, sprout yield of 5.3 g/ g seed, hypocotyl length >13 cm, hypocotyl thickness> 1.5 mm and molds < 60% . V12-1789 and V09-3876 showed good sprout characteristics and decent agronomic traits, so they could be the promising sprout varieties for further evaluation.