Abstract
:The plasticity in root system development (RSD) is a key trait for the adaptation of rice to mild drought. However, the enhanced RSD due to the plasticity may not be always a sole function of promoted lateral root (LR) production, but also of the integrated responses of nodal root (NR) development. In this study, we aimed to evaluate the effects of mild drought intensities on the development of the NR and LR, and their contribution to the entire RSD. We used six genotypes including KDML105 (indica, lowland adapted), a high lateral rooting ability genotype. The plants were grown up to heading or maturity stage for two years under soil with limited soil depth (20 cm) assuming the presence of the hardpan and at different moisture gradients generated by the line source sprinkler system. The effects of drought intensities generally differed between the development of NR and LR. In both years, all genotypes showed highest LR development under mild drought stress intensities. However, in some genotypes including KDML105, NR development was maintained in a limited soil moisture range only, which was narrower and wetter than that in which LR plasticity was expressed. Furthermore, the entire RSD was maintained only when both the NR and LR were simultaneously promoted or maintained. These results suggest that the NR have less plasticity than the LR in response to drought and the contribution of the plasticity in LR development to the entire RSD is dependent on both the soil moisture and nodal rooting ability.
Highlights
It is estimated that about one third of world rice area is rainfed lowlands and mostly prone to drought (Maclean, Dawe, Hardy, & Hettel, 2002)
We showed that the phenotypic plasticity in lateral root (LR) development under heterogeneous soil environment with limited soil depth is a key trait that effectively contributed to plant dry matter production through increased total root length (TRL) and water uptake, especially under mild drought stress (Kano, Inukai, Kitano, & Yamauchi, 2011; Kano-Nakata, Inukai, Wade, Siopongco, & Yamauchi, 2011)
We aimed to compare the effects of mild drought intensities on the developmental responses between the nodal and LRs, which may differently contribute to the entire root system development (RSD), under lowland rice fields where the hardpan normally exists at about 20 cm deep (Kato et al, 2013)
Summary
It is estimated that about one third of world rice area is rainfed lowlands and mostly prone to drought (Maclean, Dawe, Hardy, & Hettel, 2002). We showed that the phenotypic plasticity in LR development under heterogeneous soil environment with limited soil depth is a key trait that effectively contributed to plant dry matter production through increased total root length (TRL) and water uptake, especially under mild drought stress (Kano, Inukai, Kitano, & Yamauchi, 2011; Kano-Nakata, Inukai, Wade, Siopongco, & Yamauchi, 2011). Plasticity in LR development is expressed under mild stress condition (Kano et al, 2011; Kano-Nakata et al, 2011), the response of nodal root to different drought intensities maybe different from that of the LRs. In this study, we aimed to compare the effects of mild drought intensities on the developmental responses between the nodal and LRs, which may differently contribute to the entire RSD, under lowland rice fields where the hardpan normally exists at about 20 cm deep (Kato et al, 2013). For the precise control of drought intensity, we used line source sprinkler (LSS) system (Lanceras, Pantuwan, Jongdee, & Toojinda, 2004; Kano et al, 2011) that can create the smooth gradient from wet to dry soil conditions
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