Evaluation and classification of leaflet shape and size in wild soybean

Two gene pairs are known to affect leaflet shape in soybean [Glycine may (L.) Merr.], but only two categories of leaflet shape are routinely used to characterize soybean germplasm. Very little information has been published about leaflet shape and size for wild soybean (Glycine soja Sieb. & Zucc.) accessions in the USDA Soybean Germplasm Collection but these characteristics have been shown to be among the most diverse morphological traits in the Chinese G. soja collection. The objectives of this research are to evaluate and establish a visual classification system for the variation of leaflet shape and size in the USDA Soybean Germplasm Collection. In 1998 and 1999, 661 wild soybean accessions from the USDA Soybean Germplasm Collection in maturity groups 000 through IX were grown at either Urbana, IL, or Stoneville, MS. Images of fully expanded terminal leaflets were recorded with a digital camera after all accessions were in the reproductive phase. Representative leaflets were selected at approximately two-thirds of the distance from the ground to the top of the plant. Images were analyzed by the computer software Image-Pro Plus (Version 3.0). Six measured or calculated parameters were recorded. The FASTCLUS procedure of SAS was used to define appropriate categories of leaflet shape and size. Length/width ratio and length were chosen to define leaflet shape and leaflet size, respectively. Length/width ratio values ranged from 1.3 to 6.2 and length from 3 to 14 cm. Five categories of leaflet shape are proposed: oval, ovate, lanceolate, linear, and ultra linear; and three classes for leaflet size: small, intermediate, and large. Leaflet shape and leaflet size are associated with geographical origin. Accessions from South Korea were generally smaller than those from China, Japan, and Russia. Accessions from China had more leaflet variation than those from South Korea or Japan but those from Russia were the most variable. Nearly all of the accessions with lanceolate and linear leaflets originated from Russia.