Morphological Characterization and Genetic Diversity Assessment in Rice (Oryza sativa L.) Genotypes Using DUS Descriptors

Abstract

The study was conducted to assess morphological variability among seventy-seven rice (Oryza sativa L.) genotypes using thirty-two qualitative traits in accordance with the Distinctness, Uniformity, and Stability (DUS) guideline. The study aimed to quantify phenotypic diversity through genotype frequencies, percentage contribution and the Shannon–Weaver Diversity Index (SWDI) and to identify key descriptors useful for varietal distinctness and selection in rice breeding programs. The results revealed considerable variation in several reproductive and panicle-related traits, whereas most vegetative and pigmentation traits exhibited uniform expression. Traits such as leaf auricle, ligule, collar, and stem anthocyanin colouration were monomorphic, showing 100% uniformity with zero diversity (SWDI = 0.00), indicating linkages of the concern gene based on genomic constitution across the genotypes. In contrast, panicle attitude of branches exhibited pronounced polymorphism, with spreading (76.81%), semi-erect to spreading (8.70%) and erect (5.80%) types, and recorded the highest diversity index (SWDI = 0.85). Moderate diversity was observed for lemma pubescence density (strong 82.61%, medium 11.59%; SWDI = 0.57), panicle exertion (well exerted 84.06%, mostly exerted 10.14%; SWDI = 0.54) and grain shape (medium slender 86.96%, long slender 8.70%; SWDI = 0.50). Most genotypes were awnless and exhibited straw-coloured lemma and palea (98.55%), reflecting low variability (SWDI = 0.08). Overall, the SWDI values ranged from 0.00 to 0.85, indicating variable levels of phenotypic diversity across the descriptors studied. The findings suggest that traits exhibiting higher diversity—particularly panicle attitude of branches, lemma pubescence, panicle exertion and grain shape, can serve as key indicators for genotype identification, varietal protection and selection of diverse parental lines in rice breeding programs aimed at enhancing distinctness and broadening the genetic base of cultivated rice.