Phenotypic and Molecular Diversity of Commercial Yardlong Bean [Vigna unguiculata (L.) Walp. Subsp. sesquipedalis] Hybrids for Breeding Utilization

Yardlong bean [Vigna unguiculata (L.) Walp. subsp. sesquipedalis] is a significant vegetable legume in Southeast Asia, where breeding programs focus on pod length, yield and uniformity. Prolonged selection for uniform commercial traits may progressively reduce genetic variability within hybrid germplasm if not systematically monitored.

Twenty commercial F₁ yardlong bean hybrids were evaluated using seventeen morphological traits. Multivariate analyses (correlation, UPGMA and principal component analysis) were performed to assess phenotypic structure. Genetic diversity was examined using nuclear ITS, chloroplast psbA-trnH and RAPD markers.

Morphological differentiation was moderate and primarily driven by pod-related quantitative traits, particularly pod length and pod weight. DNA barcoding confirmed species identity with complete sequence conservation among hybrids. RAPD analysis revealed substantial polymorphism (79.42%) and genetic similarity coefficients ranging from 0.46 to 0.96, indicating detectable genetic variation among hybrids. However, RAPD is a dominant marker system with limited reproducibility; therefore, validation using co-dominant markers, such as SSR or SNP, is recommended. Hybrids Y15, Y16 and Y18 combined superior pod traits with high genetic similarity, while Y12 and Y20 were genetically distinct. The results indicate that phenotypic similarity does not necessarily reflect genomic similarity. A combined analytical framework integrating phenotypic evaluation with molecular data provides a more reliable basis for germplasm characterization and breeding decisions.