Comprehensive Analysis of Trait Associations and Path Coefficients for Yield, Quality, and Biotic Stress Resistance in Onion (Allium cepa L.) Genotypes under Short-Day Conditions

Abstract

Onion (Allium cepa L.) is a globally important vegetable crop where yield improvement depends on multiple morphological, quality, and resistance traits. The study investigated 18 onion (Allium cepa L.) genotypes in order to determine correlations and path coefficient associations between yield, quality, and resistance parameters under short-day circumstances. Genotypic correlations were frequently larger than phenotypic correlations, indicating that genetic relationships were somewhat obscured by environmental factors. The number of leaves had substantial positive connections with polar diameter, equatorial diameter, bulb weight, and yield features, indicating its role in assimilate production. Among bulb features, equatorial diameter had the strongest relationship with bulb weight and yield, with bulb weight exhibiting a nearly perfect connection (r > 0.95) with both marketable and total yield. Neck diameter correlated positively with days to maturity but negatively with reducing sugars, total sugars, and pyruvic acid, indicating a maturity-quality trade-off. Quality characteristics like reducing sugars and total sugars were substantially connected (r > 0.90), although pyruvic acid had a somewhat favourable relationship with yield traits. Biotic stress measures had a considerable impact on production, with thrips infestation and Stemphylium blight incidence showing strong negative associations with bulb size and yield. A positive correlation between thrips and illness severity demonstrated their combined negative influence. Average bulb weight was shown to be the most significant characteristic with the greatest direct positive impact on yield (1.036), followed by bulb diameter (0.734) and number of leaves (0.793). On the other hand, Stemphylium blight (–0.649) and thrips infestation (–0.738) had significant detrimental direct impacts. The results indicate that onion yield may be increased by selecting for higher bulb weight, more leaves, larger bulb diameter, and resistance to key pests and diseases.