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

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.

Keywords: aus; drought; leaf rolling; rice; tropical japonica.

Figure 1

Relationship between ΔNDVI and CT within a panel of ~220 aus rice genotypes in three field dry seasons under drought stress: (a) 2010 (ΔNDVI 68–74 DAS, CT 76 DAS); (b) 2011 (ΔNDVI 83–89 DAS, CT 89 DAS), (c) 2012 early maturing group (ΔNDVI 64–70 DAS, CT 70 DAS); (d) 2012 medium maturing group (ΔNDVI 71–74 DAS, CT 74 DAS). Twenty‐six genotypes selected for detailed measurements from the first field season are indicated by blue circles. Values shown are genotypic means

Figure 2

Volumetric soil moisture (θ_v) in the 2012 early field drought stress treatment (30 cm in depth), normalized for the initial reading in each plot (a), and gravimetric soil moisture (b) in the drought stress treatment of greenhouse lysimeters for selected aus genotypes belonging to different leaf rolling groups (low = blue, high = red) selected based on previous leaf rolling scores and ΔNDVI values. In the field study, genotypes with a greater degree of leaf rolling under drought were ARC 14088, Dangar, and Moshur, and those showing a lesser degree of leaf rolling were Biranj and Lakhsnikajal. In the greenhouse lysimeter study, genotypes with a greater degree of leaf rolling under drought in the greenhouse included Chengri 2, Dhala Bhadoi, Dangar, Goai, and Tak Siah. Genotypes with a lesser degree of leaf rolling in the greenhouse lysimeter study included Brown Gora, IC27525, Lakhsnikajal, Sufaid 246, and Solay Ghat

Figure 3

Leaf anatomy of selected aus genotypes contrasting in their propensity for leaf rolling under drought stress. (a,b) Genotypes varying in sclerenchyma cell area and number as measured in the 2018DS well‐watered field study. (c,d) Genotypes varying bulliform cell height and small vein parameters as measured in the drought stress treatment of the 2012WS field study. B, bulliform cell; BSC, bundle sheath cell; Scl‐ab, abaxial sclerenchyma cell; Scl‐ad, adaxial sclerenchyma cell; SV‐IVD, interveinal distance between small veins. Quantitative values are shown in Tables S3, S7, and S8

Figure 4

Manhattan plots and quantile‐quantile plots of genome‐wide association analysis in the aus panel for (a,b) leaf rolling score in the greenhouse lysimeter study, (c,d) change in NDVI in the 2011 field drought trial, and (e,f) leaf rolling score in the 2012 field drought trial on medium‐duration genotypes (106 DAS)