Intra-Cultivar Selection within a Natto Soybean Cultivar to Improve Agronomic and Quality Characteristics.

Natto soybean [Glycine max (L.) Merr.] cultivars are small-seeded and primarily grown for export to Japan to produce a fermented soyfood called Natto. Single-plant evaluation and selection was performed within the natto cultivar ‘MFS-591’ that has been the dominant natto soybean cultivar in the Mid-Atlantic region with the objective to improve certain desirable quality characteristics and other agronomic traits. Selection started in 2008 in a total of 2000 single plants from foundation seed of the cultivar MFS-591 that were grown in Blacksburg in a honeycomb design with plants spaced 0.9 m apart (1.4 plants/m²). Plants were harvested individually and each plant yield was adjusted based on the mean yield of its 54 surrounding plants according to the honeycomb design layout. A total of 116 plants were selected and evaluated in single row plots in 2009 in a randomized complete block design (RCB) with 3 replications. Data were recorded on seed yield and other agronomic and natto quality traits. The 22 most promising selections were grown in 2010 in RCB trials in two locations and will also be evaluated in 2011 in RCB trials in four locations. Statistically significant variation was found among the selections for maturity, plant height, seed size, water absorption, and seed coat deficiency. Some selections had earlier maturity, while others combined smaller seed weight and higher water absorption and they can be released as improved versions of the original cultivar MFS-551 where selection started.