Leaf morphology, rather than plant water status, underlies genetic variation of rice leaf rolling under drought.

Andrew J Cal,Rolando O Torres,Delphine Luquet,Amelia Henry,Kenneth L Mcnally,Maria Camila Rebolledo,Millicent Sanciangco

doi:10.1111/pce.13514

Abstract

Soil drying causes leaf rolling in rice, but the relationship between leaf rolling and drought tolerance has historically confounded selection of drought‐tolerant genotypes. In this study on tropical japonica and aus diversity panels (170–220 genotypes), the degree of leaf rolling under drought was more affected by leaf morphology than by stomatal conductance, leaf water status, or maintenance of shoot biomass and grain yield. A range of canopy temperature and leaf rolling (measured as change in normalized difference vegetation index [ΔNDVI]) combinations were observed among aus genotypes, indicating that some genotypes continued transpiration while rolled. Association mapping indicated colocation of genomic regions for leaf rolling score and ΔNDVI under drought with previously reported leaf rolling genes and gene networks related to leaf anatomy. The relatively subtle variation across these large diversity panels may explain the lack of agreement of this study with earlier reports that used small numbers of genotypes that were highly divergent in hydraulic traits driving leaf rolling differences. This study highlights the large range of physiological responses to drought among rice genotypes and emphasizes that drought response processes should be understood in detail before incorporating them into a varietal selection programme.

Highlights

Rice leaves typically show increasing degrees of leaf rolling in response to increasing severity of drought stress (DS)
This study allowed the comparison of multiple physiological drought response parameters, and because the aus and tropical japonica panels have been genotyped for single nucleotide polymorphism (SNPs), genomic regions were associated with leaf rolling under drought
We explored how previously reported genes from the literature might be linked to the candidate genes from the aus and tropical japonica genome‐wide association study (GWAS) using RiceNet v2 (Lee et al, 2015) using the identified candidate genes from each panel and loci previously reported to be involved in leaf rolling as seed loci (Tables S15 and S16)

Summary

| INTRODUCTION

Rice leaves typically show increasing degrees of leaf rolling in response to increasing severity of drought stress (DS). O'Toole and Cruz (1979) reported that transpiration rate per unit leaf area decreased increased when rice leaves were manually rolled and unrolled, leading the authors to conclude that the boundary layer formed upon rolling had a stronger effect than stomatal closure on transpiration of rolled leaves. Despite the strong genotypic effect reported on rice leaf rolling in response to drought, little is known about the genetics related to this trait, and previous physiology studies have included only 1–7 genotypes. This study allowed the comparison of multiple physiological drought response parameters, and because the aus and tropical japonica panels have been genotyped for single nucleotide polymorphism (SNPs), genomic regions were associated with leaf rolling under drought

| MATERIALS AND METHODS

| RESULTS

Findings

| DISCUSSION