Relevance of acquired tolerance traits and root length in determining spikelet fertility and yield in rice

Drought tolerance, from an agronomic viewpoint, has always been associated with the maintenance of yield under water-limited conditions. Whereas, for sustained crop improvement, a trait-based breeding program should be the primary focus. One of the key contributors to the drop in yield under water-limited aerobic cultivation is the loss of spikelet fertility. To reduce spikelet sterility acquired tolerance traits (ATTs) should be considered along with constitutive traits for maintaining the water status and metabolic activity. Due to the lack of facility to induce a stress that mimics field conditions, genetic diversity in ATTs under gradually progressing moisture stress conditions is an unexplored area. The phenomics facility in our centre was used to impose the specific soil moisture regimes precisely to characterize genetic diversity in a 21 germplasm lines from IRRI 3 K rice genome panel for the root system and ATTs. Our findings revealed significant variation in all the measured ATTs. The maximum root length was measured as the deep root system is considered to be desired trait for a water limitation. We clearly indicate that the group of genotypes with a better root system combined with higher ATTs can significantly improve spikelet fertility and thus yield under semi-irrigated aerobic conditions. We also demonstrated using a seedling level experiment that, genotypes with greater root length during water limitation at the reproductive stage had maximum root length during the initial stage of growth. This study demonstrates the relevance of combining multiple traits to achieve higher productivity under water limitations.