Biochemical characterization of onion (Allium cepa L.) genotypes: Implications for breeding high-nutrient varieties

Numerous onion varieties are cultivated in India, exhibiting variations in antioxidant levels due to genetic and environmental factors. The health benefits associated with these antioxidant compounds motivate breeders to identify genotypes with superior functional properties. In the present study, we have attempted to characterize variations in biochemical compounds in different onion genotypes. Significant variations (p≤0.05) were observed in the phenolic content, anthocyanins levels, and activities of biosynthetic enzymes [(phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL)] among thirty onion genotypes grown under sub-tropical Indian conditions. Among the red genotypes, namely D-305-B, Rec-1404, and PRO-6, high phenolic content, with a mean exceeding 0.7 g/100g DW, was observed. Genotypes Rec-1404 and PRO-6 exhibited the highest mean flavonol and ODH levels. Yellow genotypes POH-4 and POH-5 displayed high quercetin content. Anthocyanins levels were notably high in genotypes PRO-6 and Pb. Naroya. The highest PAL and TAL activities were recorded in the red genotypes D-888-B and Rec-1404, with mean activities exceeding 1.25 units. Total phenols exhibited positive correlations with ODH (r=0.902), flavonols (r=0.862), and anthocyanins (r=0.571). Additionally, TAL enzyme activity showed positive correlations with total flavonols (r=0.493) and anthocyanins (r=0.446). Overall, the red genotype PRO-6 emerges as a promising candidate for breeding programs aimed at developing onion varieties with high phenolics content. By prioritizing antioxidant-rich red genotypes and emphasizing phenolics content as a key parameter, breeders can contribute to the development of onions with enhanced health-promoting properties.