Evaluating the resistance of six rice cultivars to drought: restriction of deep rooting and the use of raised beds

Abstract

Soil water deficits reduce rice (Oryza sativa L.) productivity under upland field conditions. In this study, we constructed screening facilities to evaluate the performance of rice cultivars under drought conditions and to assess the roles of deep roots. Two experiments were conducted with six rice cultivars, including drought-tolerant and drought-susceptible cultivars, grown in two root environments: a rootrestricted treatment that restricted rooting depth with water-permeable sheets, and a raised bed that reduced water availability in the surface soil by inserting a gravel layer between the topsoil and subsoil layers to interrupt capillary transport of water. In the rootrestricted treatment, in which root growth was restricted to the surface 25-cm layer, leaf water potential decreased faster in cultivars with a large canopy during drought stress, and there was little difference in panicle weight among cultivars. With a normal (unrestricted) root environment, the deepestrooting cultivar ('IRAT109') maintained higher leaf water potential during drought, although panicle weight under drought stress was affected by yield potential as well as by deep rooting. Under the intermittent drought stress in the raised bed, deeprooting cultivars accumulated more nitrogen and produced more biomass, and the difference in panicle weight between deep-rooting drought-tolerant and shallow-rooting drought-susceptible cultivars was magnified by the raised bed compared with the yield differences under drought in a normal root environment. These results demonstrate that the drought screening facilities we developed can help to identify superior cultivars under upland field conditions without time-consuming measurement of deep root systems.

Matching the Expression of Root Plasticity with Soil Moisture Availability Maximizes Production of Rice Plants Grown in an Experimental Sloping Bed having Soil Moisture Gradients

“…These genotypes were IRAT109 (upland-adapted japonica) and KDML105 (lowlandadapted indica). In our previous study, KDML105 (lowland type) showed greater root plasticity especially at the shallow soil depths (Bañoc et al, 2000;Kano-Nakata et al, 2013) while IRAT109 (upland type) showed faster root elongation rate (Bañoc et al, 2000) and greater deep root ratio (ratio of deep root length below 30 cm depth to total root length) (Kato et al, 2006(Kato et al, , 2007. The seed sowing, seedling management and transplanting were done in a similar manner to those in Experiment 1.…”

“…5) contributed to its higher efficiency for water uptake when grown at the highest position in the toposequence, because it could take advantage of the available soil moisture deep down below the soil surface (Kato et al, 2007). Thus, the maintenance of dry matter production even at the high position in the toposequence in IRAT109 (Fig.…”

“…This plasticity in root system development is functionally effective and efficient for the enhancement of water uptake especially under mild water deficit conditions (Kano-Nakata et al, 2011). On the other hand, it has been well established that deep rooting avoids drought-induced stress by extracting available water from the deep soil layers (Azhiri-Sigari et al, 2000;Kato et al, 2007;Gowda et al, 2011). A typical example of advantageous effects of deep rooting were recently reported by Uga et al (2011), who mapped a quantitative trait locus (QTL) for deep rooting, DEEPER ROOTING 1 (DRO1) that enables rice plants to produce more grains under drought-induced stress without yield penalty.…”

“…Thus, we developed and calibrated an experimental sloping bed that can create a gradient of available water both along the soil surface and along the vertical soil profile by manipulating the ground water level in the sloping bed. Then, we also used contrasting genotypes in terms of root plasticity expression in response to drought stress; KDML105 (lowland type), which has known root plasticity expression at the shallow soil layer (Bañoc et al, 2000;Kano-Nakata et al, 2013) and IRAT109 (upland type), which has known deep root development under drought stressed upland conditions (Kato et al, 2006(Kato et al, , 2007. We expect that under an increasing toposequence where moisture availability shifts from shallow to deeper soil layers, the shoot dry matter production of KDML105 may be reduced while that of IRAT109 is maintained.…”

Suppression of Tillering in Erianthus ravennae (L.) Beauv. Due to Drought Stress at Establishment

“…The soil in the greenhouse was a humic andosol which had dark and humic silty loam in topsoil layer and red-brown silty clay loam in subsoil layer. The hydraulic properties of the soil were previously reported (Kato et al, 2007). Each greenhouse had 24 plots (1.5 m ×3.6 m) inside, and the divided stubbles of E. ravennae were planted in 3 plots of them at a rate of 6 plants plot -1 in each greenhouse.…”