Genetic Variability and Diversity in Red Onion (Allium cepa L.) Genotypes: Elucidating Morpho-Horticultural and Quality Perspectives

Abstract

Onion (Allium cepa L.) is a prominent spice and vegetable crop farmed commercially worldwide. Variability is viewed as a key signal for any red onion enhancement effort. The current study was, therefore, carried out to learn about genetic variability and diversity among selected genotypes of 20 red onions at the C Block Farm, Bidhan Chandra Krishi Viswavidyalaya, India, during the winter (rabi) season of 2021–2022, in Randomized Complete Block Design (RCBD) with three replications. The characters, viz., average weight of bulbs (kg), neck thickness (cm), total soluble solids (°Brix), total sugar (%), and reducing sugar (%) demonstrated high heritability (97.38–99.97%) coupled with high genetic gain. Such traits were the least influenced by environmental effects, and additive gene action played a pivotal role in the manifestation of such characters. Traits with high heritability values (51.37–67.94%) demonstrate that the observed variability was under genetic control and provide an enormous range of possibilities for accomplishing selection depending on their phenotypic performances. For traits with moderate heritability, viz., bolting (%) and doubling (%), selection would be less effective but can still be given great importance. Based on correlation analysis, the character’s neck thickness, equatorial diameter, and polar diameter unveiled highly positive genetic correlation with the average weight of bulbs (0.120, 0.112; 0.194, 0.210 and 0.120, 0.112 for phenotypic and genotypic correlation coefficient values, respectively), which indicates that the average weight of a bulb would be increased by an increase in such components. According to path coefficient analysis, the equatorial diameter exhibited the most positive direct effect on the average weight of bulbs (0.968), followed by polar diameter (0.687) and neck thickness (0.159). A wide range of variations for qualitative traits, including foliage colour, leaf width, foliage behaviour, the degree of leaf waxiness, the shape of the bulb, and bulb skin colour were observed. Based on Mahalanobish D2 analysis, the genotypes were divided into four clusters. The highest number of genotypes was found in cluster I (eleven), followed by cluster IV (six genotypes) and cluster II (two genotypes). Cluster III had a single genotype and was monogenic. The study confirmed that a wide genetic variation prevailed in the onion genotypes taken under study, which could thereby be utilized in breeding programmes.