Growth analysis of various onion genotypes for yield and pharmaceutical traits

Abstract

Onion (Allium cepa L.) is a globally significant biennial crop cultivated as an annual, with its growth and bulb development highly sensitive to thermo-photoperiodic regulation. Understanding genotype-specific phenological responses is critical for optimizing yield and nutraceutical potential. This study characterized the growth dynamics, yield traits, and pharmaceutical compound accumulation in onion genotypes under field conditions, identifying thermo-sensitive stages and genotypic variability. A field experiment was conducted at PMAS Arid Agriculture University Rawalpindi, Pakistan, using a randomized design. Seven genotypes were evaluated for morphological (plant height, leaf count, bulb weight), physiological (CGR, NAR), and pharmaceutical traits (phenolics, flavonoids) at 7-day intervals until harvest. Vegetative growth peaked at 97 days after transplanting (DAT), with bulbing initiation triggered by rising temperatures (>25°C).104 DAT emerged as a critical thermo-sensitive stage, where heat stress significantly reduced bulb yield (15-20%) and altered secondary metabolite profiles. SWAT-1 outperformed other genotypes, exhibiting 22% higher yield and 30% greater flavonoid content, linked to sustained crop growth rate (CGR) during bulbing. Pharmaceutical compounds peaked during late vegetative growth (75-90 DAT) but declined post-bulbing, indicating a trade-off between storage organ development and defense metabolite production. The 97-104 DAT window is pivotal for yield stability and nutraceutical quality, with genotypic divergence in thermal resilience. SWAT-1’s robust performance underscores its potential for breeding programs targeting climate adaptation and enhanced phytochemical content.