Variability, heritability and trait association studies for bulb and antioxidant traits in onion (Allium cepa) varieties

Onion (Allium cepa L.) is one of the most important vegetable having year round demand and consumed fresh, cooked or processed. It occupies maximum area under vegetables in India. The consumption of onion has been associated with many health benefits. The genetic improvement work mainly focused on improving yield and there has been little effort on improving quality traits. Therefore, information on variability, heritability and trait association of phytochemicals content, antioxidant activity and bulb traits are lacking. The present study was conducted to bridge the gap and generate information on these aspects. A total of eight quality traits and four bulb traits were analyzed in 22 onion genotypes of five different skin colour. The genotypes were procured from diverse geographic region. The total soluble solids content (TSS), pungency, total phenol, flavonoids content, and antioxidant activities as estimated through CUPRAC and FRAP in the onion varieties varied from 10.13-16.65 °Brix, 4.67-12.28 μmol Pyruvic acid/g FW, 740.67-1145.33 μg Gallic acid equivalent/ml, 31.67 - 465.0 μg Quercetin equivalent/ml, 2.23 - 5.14 μmol Trolox/g and 1.60-4.63 μmole Trolox/g, respectively. There was less difference between phenotypic and genotypic components of variance for pungency, total phenols, antioxidant activity and juice recovery, suggesting greater role of genotype in the expression of quality traits and better scope of improvement for these traits. The high heritability estimates (>75%) for bulb diameter, total phenols, flavonoids, pungency and antioxidant activity, and higher value of genotypic correlation co-efficient over phenotypic co-efficient supports greater role of genotype in the expression of quality traits. The high estimate of heritability and comparatively, low estimate of genetic advance and genetic gain suggest the role of both additive and non-additive gene action. Thus hybridization and selection would be the best strategy to improve quality traits in Indian onion genotypes. Future breeding attempt to develop onion varieties with higher health benefits should focus on medium sized varieties without compromising on yield.