Rice leaf structural adjustment to sustain photosynthetic traits under drought and produce more grain: Evidence from field studies of the 3K indica panel

Understanding plant traits that contribute to maintenance of physiological activities under drought is crucial for sustainable rice production. Leaf morphological characters together with UAV-based HTP measurements of canopy temperature (CT) and NDVI, leaf water potential (ψLeaf), photosynthetic traits including A, gs E and Ci, and drought response index (DRI) were collected from > 600 indica genotypes in two field dry seasons. This dataset from the 3 K rice sequenced genomes under well-watered (WW) and managed drought stress (MDS) revealed drought-induced leaf morpho-functional interactive changes related to grain yield under drought. Onset of drought caused ~14–20% reduction in Ci and 35 – 56% reduction in A causing serious loss in yield. Correlation analyses from two years of field dry seasons revealed that the combination of initially broader leaves capable of increasing leaf thickness in response to drought, as evidenced by changes in SLA, together with maintenance of ψLeaf, supporting a higher Anet, can collectively drive a higher DRI. The SLA changes ranged up to ~50% in one of the best performing genotypes with high DRI values upon severe drought stress. GWAS identified seven QTLs for DRI which include known drought-responsive aquaporin, dehydrin, and heat shock protein genes, which coincide with the GWAS interval identified for CT on chromosome 7. This study identified a tentative pathway linking genomic loci to water balance, leaf development, and photosynthesis-related traits under drought. Our results provide opportunities to select the best-performing rice genotypes and enhance understanding about how to improve grain yield of rice under drought by mechanistic exploration, to aid drought breeding efforts by selecting optimal haplotype combinations or gene edits.