Beyond protein concentration: should amino acid composition be a direct breeding target in grain legumes?

Increasing seed protein concentration (SPC) is an important breeding objective in many grain legumes. However, improvement in protein quantity does not necessarily result in improvement in its amino acid composition and resulting protein quality. This raises the practical breeding question of when direct selection for protein quality provides sufficient value beyond protein concentration. Evidence across pulse crops, together with comparative evidence from soybean, shows that relationships between protein and amino acid composition depend on the crop, genotype, individual amino acid, and basis of measurement. Individual amino acid concentrations also differ in genetic variation, environmental stability, relationships with agronomic performance, and their potential nutritional value. This mini review examines these factors from a breeding perspective, with emphasis on the genetic basis of amino acid composition, multi-environment selection, agronomic compatibility, and the interpretation of amino acid concentration in relation to protein quality. We further consider how phenotyping requirements, processing, nutritional quality and value chain recognition influence the practical deployment of amino acid composition as a breeding target. Rather than treating amino acid improvement as a universal objective, we propose a framework for determining when amino acid composition warrants direct selection and whether achievable genetic gain can provide meaningful nutritional return.