Quantitative evaluation of plastic root responses to contiguous water gradient in rice

Abstract

Root plasticity is the key trait for plant adaptation to environmental stresses. To quantify phenotypic plasticity to its full extent in potential, it needs to be evaluated under contiguous environmental changes. For that purpose, we used the combination of chromosome segment substitution lines (Nipponbare/Kasalath CSSLs) and line source sprinkler (LSS) system of irrigation. For analysis, we first attempted to apply the coefficient of variation (CV) and norm of reaction that have been used as the conventional approaches, and then propose a new approach for quantification of root plasticity. Results revealed that CV was not linked to root plasticity under contiguous water gradient in this study. In contrast, norm of reaction was linked to root plasticity and better explained with curve than linear, especially for CSSL50 (the most plastic genotypes) under such gradient. Based on the norm of reaction with curve, root plasticity was calculated using the difference in total root length between CSSLs and the recurrent parent, Nipponbare. Further analysis of root plasticity in relation to dry matter production was also done. By applying the new approach, we confirmed that root plasticity expression was affected by the intensities of drought stress and genotypes, indicating that such root plasticity is genetically controlled. In addition, root plasticity effectively contributed to the dry matter production under the drought conditions and maximized at around 20% of soil moisture content (-0.04 MPa). By using CSSLs and LSS system, we successfully evaluated root plasticity under contiguous water gradient.

Functional roles of root plasticity and its contribution to water uptake and dry matter production of CSSLs with the genetic background of KDML105 under soil moisture fluctuation

“…Previous studies have shown experimental evidences of genotypic variations in root plasticity expressed in response to heterogeneous soil environments for the adaptation of rice plants (Bañoc et al, 2000a;Siopongco et al, 2008;Kano-Nakata et al, 2013;2017;Kameoka et al, 2015;Menge et al, 2016;Niones et al, 2012;Nguyen et al, 2018;Owusu-Nketia et al, 2018;Suralta et al, 2010Suralta et al, , 2016Suralta et al, , 2018Tran et al, 2014). In this study, the CSSLs showed no significant differences in root system development with the recurrent parent under CWL in both experiments.…”

Genomic-based root plasticity to enhance abiotic stress adaptation and edible yield in grain crops

“…Three chromosome segment substitution lines from upland rice cultivar 'Kasalath' (CSSL45, 47 and 50) in the background of cultivar 'Nipponbare' were associated with increased shoot dry weight than the control when under water deficit conditions. This response indicated that plasticity in root system development enhanced water uptake ability in mildly droughted soil [13,27,28]. Similarly, plasticity in root system development of introgression lines (ILs) ILsYTH183 and IL-sYTH304 in shallow soil layers contributed to the greater shoot dry weight over that of the background cultivar IR64, with ILsYTH183 showing rapid increases in root elongation and branching when rewatered after drought, which contributed to its higher shoot dry matter production and water extraction compared to IR64 [29].…”

“…Trait standard deviation Trait mean 100 and norm reactions. In a set of chromosome segment substitution lines of rice grown under a continuous water gradient, the CV did not provide a good measure of root plasticity, but a non-linear curve of the reaction norm did [13]. Path analysis has been proposed for measuring plasticity resulting from selection [14].…”

Genotypic variations in the plasticity of nodal root penetration through the hardpan during soil moisture fluctuations among four rice varieties

“…Nipponbare and Kasalath are the parents of a set of Chromosome Segment Substition Lines (CSSLs). Using this set of CSSLs derived from a cross between Nipponbare and Kasalath, several studies have precisely quantified the root plasticity with minimal effects of genetic confounding (Kano-Nakata et al, 2011Kano-Nakata et al, 2017;Tran et al, 2014Tran et al, , 2015, as well as the detection of QTLs associated with root plasticity (Niones et al, 2013(Niones et al, , 2015. On the other hand, Sasanishiki and Habataki are the parents of another set of CSSLs (http://www.rgrc.dna.affrc.go.jp/ jp/).…”