Deep rooting in bread wheat is more strongly associated with genotypes than drought stress: evidence from Van Lake Basin genotypes

Drought stress is a major constraint limiting bread wheat productivity in semi-arid regions, where improved root system architecture is increasingly recognized as a key component of climate resilience. However, it remains unclear whether deep rooting is primarily a genetically determined trait or a plastic response induced by drought stress. This study tested the hypothesis that genotypic background exerts a stronger influence on deep rooting patterns than water deficit itself in bread wheat. Nine genotypes, including seven locally adapted landraces from the Van Lake Basin and two standard cultivars, were grown under controlled greenhouse conditions under well-watered and drought treatments, and root distribution was quantified at three soil depths (0-30, 30-60, and 60-100 cm). Deep root index was not significantly affected by water treatment alone, whereas genotype and genotype × water interaction effects were highly significant, indicating a strong genotype-dependent pattern of root depth allocation. Genotypes showed contrasting drought responses: Bitlis 1-4 increased deep root allocation from 39.8% to 53.1% under drought, while Bitlis 9-1 declined from 44.3% to 32.1%. Associations between root traits and grain yield were weak, suggesting that root system size alone is insufficient to explain drought adaptation. Overall, the results demonstrate that deep rooting in bread wheat is predominantly genotype-dependent rather than uniformly drought-induced. These findings identify promising germplasm with genotype-specific root responses under drought from the Van Lake Basin and provide a basis for integrating root distribution traits into breeding programs aimed at improving wheat performance under water-limited environments.