GWAS for root yield and its contributing traits in Withania somnifera (L.) dunal: First report

Ashwagandha [Withania somnifera (L.) Dunal] is a significant medicinal plant, with limited information on its genetic variability. This study evaluateed genetic diversity among 96 ashwagandha genotypes with the aim of developing strategies to improve root yield and secondary metabolites. A joint ANOVA indicated significant variability within the evaluated panel. Key traits, such as root girth, fresh root yield and dry root yield showed positive and significant correlations at both tested years. Molecular markers (SRAP, ISSR, and SSR) were used to assess genetic diversity. Amplified PCR products ranged from 210 bp (SRAP-22) to 1350 bp (SRAP-19), with PIC value ranged from 0.332 (SSR 20) to 0.494 (ISD 11), indicated moderate informativeness of markers. Genetic diversity analysis using Dice's coefficient formed six clusters, identifying two genotypes (86 and 87) as highly diverse. Population structure analysis revealed five clusters with an Fst range of 0.21-0.36, indicating allele flow among genotypes. The highest genetic differentiation was observed between clusters G2 and G4 (Fst = 0.1253). On the basis of structure analysis, genotypes in cluster G5 exhibited similar genetic make-up. A genome-wide association study (GWAS) identified a 490 bp locus of the SRAP 49 marker as highly effective and informatice. This locus was broadly associated with fresh root yield (FW) and dry root yield (DW) across individual and pooled environments. The positive correlation between these traits suggests simultaneous improvement is feasible. This study highlights the importance of genetic diversity for enhancing root yield and provides valuable insights for the genetic improvement of ashwagandha.