Single-Plant Selection at Ultra-Low Plant Density within a Natto Soybean Cultivar to Improve Seed Yield and Quality.

Natto soybean [Glycine max (L.) Merr.] cultivars are small seeded and seed yield is generally lower than oilseed cultivars. They are primarily grown for export to Japan to produce a fermented soyfood called Natto. ‘MFS-591’ has been the dominant natto soybean cultivar in the Mid-Atlantic region for over 10 years. Compared to oilseed cultivars, it is small-seeded (<10g/100 seeds), has acceptable high water absorption, higher protein, but lower seed yield, and later maturity.  Anecdotal evidence suggests MFS-591 yields have declined since its release.  The main objective of this study was to perform single-plant selection for higher seed yield within the natto soybean cultivar MFS-591. A secondary objective was to investigate the existence of genetic variation for seed size, maturity, and quality characteristics within the selections. In 2008, a total of 2000 single plants from foundation seed of the soybean cultivar MFS-591 were grown at the Virginia Tech Kentland College Farm in Blacksburg in a honeycomb design using a plant spacing of 0.9 m (1.4 plants/m²). Plants were harvested individually and their yield was adjusted based on the mean yield of 54 surrounding plants according to the honeycomb design. A total of 116 plants were selected and grown in single row plots in 2009 in a randomized complete block design with 3 replications. Data were recorded on seed yield and other agronomic and natto quality traits. Preliminary analysis suggests that variation within the single plants of the cultivar exists for seed yield, maturity, height, water absorption, and seed size. The most promising selections will be grown in 2010 in two locations in order to assess the benefits of single plant selection and identify lines with improved performance over the original MFS-591 cultivar.