Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/15/2003
Publication Date: 3/1/2004
Citation: Chen, Y., Nelson, R.L. 2004. Evaluation and classification of leaflet shape and size in wild soybean. Crop Science. 44:167-677. Interpretive Summary: Unlike soybean, wild soybean plants cannot be differentiated based on pubescence, flower, pod, and seed colors because there is almost no variation for these traits. Finding traits that can be easily used to classify wild soybean lines would be helpful for those maintaining germplasm collections. In this research, we found that there is great variation among wild soybean lines for both leaflet size and shape. We established a visual classification system that can put wild soybean lines into one of 15 different categories based on leaflet size and shape. By classifying the wild soybean lines in the USDA Soybean Germplasm Collections, we found associations between leaflet size and shape, and the country of origin of the wild soybean line. This research is important because it shows a simple plant characteristic that may be an indicator of significant genetic differences among wild soybean lines. This information will be useful for soybean germplasm curators who are acquiring and maintaining genetic diversity and for soybean breeders who are utilizing that diversity.
Technical Abstract: Two gene pairs are known to affect leaflet shape in soybean (Glycine max [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 using 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 S. Korea were generally smaller than those from China, Japan, and Russia. Accessions from China had more leaflet variation than those from S. Korea or Japan but those from Russia were the most variable. Nearly all of the accessions with lanceolate and linear leaflets originated from Russia.