Genetic control of root architectural traits in KDML105 chromosome segment substitution lines under well-watered and drought stress conditions

Drought is a major constraint in rainfed rice production and root architectural traits are important breeding targets for improving productivity under drought stress. A set of chromosome segment substitution lines (KDML105-CSSLs) and KDML105 were grown in the wet season at two sites (Rice Gene Discovery (RGD) and Ubon Ratchatani Rice Research Center (URRC)) in Thailand under well-watered (WW) and drought stress (DS) treatments. RGD is characterized by having a heavy clay soil type while URRC’s soil has a high percentage of sand and characterized by infertility. Root architecture traits varied within the population at both sites and exhibited plasticity in response to drought as affected by location by water regime interaction. Lateral root density increased by 77% with drought at RGD but decreased by 18% at URRC. The proportion of nodal roots that elongated more vertically increased under drought stress by 21%, at RGD. Root number per tiller was negatively associated with tiller number and biomass at RGD under drought, while lateral root density was negatively associated with biomass under drought at URRC. Eight QTL were identified for the number of nodal roots per tiller, lateral root density, and nodal root growth angle. Several candidate genes were identified by annotating the genes within the QTL regions. Our study presented genetic insights into root architectural traits with potential use in rice breeding programs for drought tolerance.

干旱是雨养水稻生产的主要限制因素，而根系构型（root architectural traits）是提升干旱胁迫下水稻生产能力的重要育种目标。本研究将一套染色体片段代换系（chromosome segment substitution lines，KDML105-CSSLs）及KDML105品种，于泰国的两个试验点——水稻基因发现中心（Rice Gene Discovery，RGD）与乌汶叻差他尼水稻研究中心（Ubon Ratchatani Rice Research Center，URRC）——在雨季开展试验，设置正常供水（well-watered，WW）与干旱胁迫（drought stress，DS）两种处理。RGD试验点土壤为重黏土，而URRC试验点土壤含沙量高且肥力低下。两个试验点的试验群体中，根系构型性状均存在变异，且其对干旱胁迫的响应具有可塑性，该可塑性受试验地点与供水模式的互作效应调控。在RGD试验点，干旱胁迫下侧根密度提升77%，而垂直伸长的节根（nodal roots）占比在干旱胁迫下增加21%；在URRC试验点，干旱胁迫下侧根密度则下降18%。在RGD试验点的干旱胁迫条件下，单蘖节根数量与分蘖数、生物量呈负相关；而在URRC试验点的干旱胁迫条件下，侧根密度与生物量呈负相关。本研究共鉴定出与单蘖节根数量、侧根密度及节根生长角度相关的8个数量性状位点（quantitative trait locus，QTL），通过对QTL区间内的基因进行注释，筛选得到多个候选基因。本研究揭示了水稻根系构型性状的遗传机制，为耐旱水稻育种提供了潜在的理论依据与应用方向。