Agronomic performance of drought-resistance rice cultivars grown under alternate wetting and drying irrigation management in southeast China

Compared to drought-susceptible rice cultivars (DSRs), drought-resistance rice cultivars (DRRs) could drastically reduce the amount of irrigation water input and simultaneously result in higher grain yield under water-saving irrigation conditions. However, the mechanisms underlying these properties are unclear. We investigated how improved agronomic traits contribute to higher yield and higher water use efficiency (WUE) in DRRs than in DSRs under alternate wetting and drying (AWD). Two DRRs and two DSRs were field-grown in 2015 and 2016 using two different irrigation regimes: continuous flooding (CF) and AWD. Under CF, no statistical differences in grain yield and WUE were observed between DRRs and DSRs. Irrigation water under the AWD regime was 275-349 mm, an amount 49.8%-56.2% of that (552-620 mm) applied under the CF regime. Compared to CF, AWD significantly decreased grain yield in both DRRs and DSRs, with a more significant reduction in DSRs, and WUE was increased in DRRs, but not in DSRs, by 9.9%-23.0% under AWD. Under AWD, DRRs showed a 20.2%-26.2% increase in grain yield and an 18.6%-24.5% increase in WUE compared to DSRs. Compared to DSRs, DRRs showed less redundant vegetative growth, greater sink capacity, higher grain filling efficiency, larger root biomass, and deeper root distribution under AWD. We conclude that these improved agronomic traits exert positive influences on WUE in DRRs under AWD.