VARIATION IN SEED PROTEIN AMONG NODES OF NORMAL-PROTEIN AND HIGH-PROTEIN SOYBEAN GENOTYPES

Current analytical techniques permit the determination of protein, non destructively on 20- to 25-seed samples, or destructively on individua l seeds of soybean [Glycine mar (L.) Merr.]. When these small seed sam ples are analyzed, within plant variability in seed protein may affect accuracy of single plant protein values. Objectives of this study wer e to: (i) determine variability in seed protein among nodes of normal- and high-protein genotypes, and (ii) determine variability in protein of seeds from different positions within pods. Seeds from a single po d at all fruiting nodes and from three positions within pods of normal and high protein genotypes were analyzed for protein content in each of 2 yr. Seed protein content increased linearly from the 6th, lowest fruiting node, to the 17th, highest fruiting node, of both normal and high-protein strains. The range in seed protein across nodes averaged 344 to 432 g kg(-1) for normal and 420 to 509 g kg(-1) for high protei n genotypes. No differences were detected in protein content among see ds within pods for any strain. The data demonstrate that analyses of s eed samples representative of the entire plant are essential to accura tely determine seed protein of individual plants. Although non-destruc tive analyses of 20-seed samples is possible, we recommend non-destruc tive analyses of all seeds from an individual plant to determine seed protein on a single plant basis.