不同供水条件下水稻幼苗根系形成的遗传分析

利用分子标记图谱对溶液培养与旱作培养（纸培养）下的水稻（Oryza sativa L.)幼苗的种子根与最长不定根长,不定根数,总根干重,根冠比等性状进行了基因定位与遗传分析。4种参数共检测到6个数量性状位点（quantitative trait loci,QTLs)与22对上位性互作位点,其中溶液培养中的最长不定根长,总根干重和旱作培养中的总根干重检测到的QTLs位点对总变异的贡献率分别为20％,23％和13％左右;旱作培养中的最长不定根长,不定根数,根冠比和溶液培养中的根冠比仅检测到上位性位点,对表型变异的贡献率在12％－61％之间,溶液培养与旱作条件下没有一个或一对检测到的QTL或互作位点完全相同,提示溶液培养和旱作条件下影响幼苗根系生长的遗传机制差异,上位性作用对旱作培养条件下的根生长具重要影响。     

大豆耐旱种质鉴定和相关根系性状的遗传与QTL定位

从301份黄淮海和长江中下游地区代表性大豆地方品种和育成品种(系)中按根系类型选取59份,在苗期干旱胁迫和非胁迫条件下对地上部和地下部性状进行2年重复鉴定,发现材料间性状隶属函数值具有丰富遗传变异,以株高、叶龄、根干重和茎叶干重隶属函数的算术平均数为抗旱综合指标从中筛选出汉中八月黄、晋豆14,科丰1号,圆黑豆等强耐旱型(1级)和临河大粉青、宁海晚黄豆等干旱敏感型(5级)材料。比根干重、比总根长、比根体积与耐旱隶属函数平均值均呈极显著正相关,可作为耐旱性的根系性状指标。利用“科丰1号×南农1138 2”(1级×4级)衍生的RIL群体为材料,对耐旱相关根系性状采用主基因 多基因混合遗传模型分离分析法进行遗传分析并进行QTL定位。结果表明,该两亲本间比根干重、比总根长、比根体积的遗传均为两对主基因加多基因模型,后两者主基因间有连锁(重组率分别为4.30%和1.93%);主基因遗传率为62.26%～91.81%,多基因遗传率为2.99%～24.75%;耐旱相关根系性状各主要由1对主基因控制,另1对效应较小。QTL分析检测到5、3、5个QTLs分别控制比根重、比根总长、比根体积,位于N6 C2、N8 D1b W、N11 E、N18 K连锁群上。3性状各有1个贡献率大的QTL(Dw1,Rl1,Rv1),而且均位在N6 C2的STAS8_3T STAS8_6T相同距离的区段上,其他QTLs效应均较小。分离分析与QTL定位的结果相对一致。     

苗期水稻根部性状的QTL定位

耐旱是水稻抗逆研究中最重要的性状之一。利用水稻籼粳品种窄叶青8号（ZYQ8）和京系17（JX17）及其通过杂交F1代花药培养获得的127个单株组成的双单倍体分离群体（double haploid,DH)为材料,在营养液中培养10天后,对影响抗旱能力的根部几个主要性状进行了分析,发现最大根长（Maximum root Length,MRL)、根干重（Dry Root Weight,DRW)和根茎干重比（Root/Shoot Ratio of Dry Weight,RSR)3个性状在群体中变异较大,利用该群体建立的水稻分子遗传图谱,对上述3个水稻性状进行数量性状座位（Quantitative Trait Locus,QTL)的分析定位,结果表明,2／1／2个QTLs的亲本JX17等位基因分别控制着最大根长、根干重和茎士重比的表达,对表型变异的解释率分别为16．4％、17．0％、16．4％、10．4％和19．9％;2／1个QTLs的亲本ZYQ8等位基因分别控制着最大根长和根茎干重比的增加,表表型变异的解释率分别为19．6％、13．0％和13．2％。检测到的8个QTLs分别位地水稻的染色体2、3、4、5、6、9和10上。与其他已发表的定位结果比较表现,在3个性状的总共8个QTLs中,各有1个性状的1个QTL（控制最大根长的L169－CT106A,控制根干重的G45－G1314A和控制根茎干重比的G62－G144）与早先报道的结果相吻合。     

绿豆产量相关农艺性状的QTL定位

绿豆育种的目标性状大多是受多基因控制的数量性状,表现型受环境影响很大。为深入分析绿豆复杂数量性状的遗传特征,本试验以绿豆Berken/ACC41 F10重组近交系群体为作图群体,利用该群体已经构建的包含79个RFLP标记的分子连锁图谱对北京和广西2个种植环境下考察的11个绿豆产量相关农艺性状进行QTL定位。结果表明,2个环境下共检测到产量相关性状QTL 63个（其中北京25个,广西38个）,分布于除第13连锁群以外的12条连锁群。大部分QTL只在单一环境下被检测到,说明产量相关QTLs与环境之间存在明显的互作。2个环境均能检测到的QTL仅有6个,分别为控制荚长、百粒重、生育期的QTLs,这6个在不同生态环境下同时发挥效应的QTLs对于绿豆分子标记辅助育种具有特殊的意义。研究还发现2个QTLs富集区域和若干成束分布的QTLs,它们可能是发掘通用QTL的候选位点。     

小麦幼苗根系形态与反复干旱存活率的关系

以35个不同栽培类型的小麦品种（系）作为试验材料,根据其6叶幼苗的根系形态性状进行聚类分析,供试材料的根系类型分为3种：大根系、小根系和中间型根系。具有中间型根系的材料反复干旱存活率最高,这些材料的根系特点是单株根数7－8．5条,最大根长20-22cm,根总干重44－48mg,其中10cm以下根干重占36％－45％,根冠比范围在0.22-0.24。一些水地栽培的育成品种苗期抗旱性较强,旱地栽培的育成品种苗期抗旱性差异较大,个别旱地栽培的地方品种在土壤水分胁迫条件下反而比在正常水分条件下的根系发育更好,可能是长期适用干旱条件的结果。     

高丹草氢氰酸含量性状的QTL定位分析

为了深入开展高丹草低氢氰酸含量性状的QTL精细定位、基因图位克隆、功能解析及分子标记辅助育种,该研究以二倍体杂交高丹草F_2代群体500个分离单株无性系及其亲本为材料,在课题组前期已构建出的高丹草高密度分子遗传连锁图谱的基础上,利用区间作图法对两年两地测定的高丹草氢氰酸含量性状进行了QTL定位分析。结果显示:(1)在4个不同环境下高丹草氢氰酸含量性状的广义遗传率分别为61.70%、72.05%、40.16%和69.25%,表明氢氰酸含量是既受环境影响又受微效多基因控制的数量性状,而且其群体测定值频率呈明显单峰正态性分布特点,符合QTL定位要求。(2)在LOD2.5的条件下,共检测到16个与氢氰酸含量性状相关的QTLs,其分布在LG1、LG2、LG4、LG6、LG7、LG8和LG10连锁群上。(3)16个QTLs中能重复检测到的稳定QTLs有9个,遗传贡献率范围为1.17%～39.9%,其中贡献率大于20%的主效QTLs有Qcn2-2、Qcn4-1、Qcn6和Qcn6-1共4个。该研究结果明确了各QTLs的遗传效应和分子标记位点。     

以回交重组自交系定位水稻萌芽期耐镉胁迫相关QTLs

水稻是世界上最主要的粮食作物之一,目前农用耕地存在土壤重金属污染的问题,而水稻对镉（Cd）等重金属的耐受性较低,进而使水稻产量和质量受到影响。定位稻种耐Cd胁迫相关数量性状基因座(quantitative trait loci, QTLs),对于指导水稻耐Cd育种具有重要意义。为发掘Cd胁迫相关基因,以粳稻02428和籼稻昌恢891衍生的124个回交重组自交系群体（backcross recombinant inbred ines,BILs）为材料,对水稻萌芽期的根长、芽长进行了分析,并对萌芽期与Cd胁迫相关的QTLs进行了定位分析。结果显示：Cd胁迫处理下,02428和昌恢891根长和芽长均受到显著抑制（P＜0.01）,其中Cd对根长的抑制强于芽长;QTL分析共检测到5个萌芽期与Cd胁迫相关的QTLs：qCdBL3、qCdRL7、qCdBL8.1、qCdBL8.2和qCdBL9分别位于水稻第3、7、8、8和9号染色体上,贡献率为6.45%~19.46%。其中,qCdBL3、qCdBL8.1、qCdBL8.2和qCdBL9与芽长相关,qCdRL7与根长相关。同时,检测到2个在对照条件下（水溶液）影响根长和芽长的QTLs：qCKBL8、qCKRL4,分别位于第8和4号染色体上,贡献率为10.53%和10.89%。比较显示,对照和Cd处理条件下控制水稻萌芽期根长或芽长的QTLs均不相同,说明Cd胁迫条件下,控制水稻根长和芽长的遗传机制可能不同于非Cd胁迫条件。研究结果为耐Cd基因的克隆和耐Cd水稻新品种的选育提供了参考。     

小麦苗期水分利用效率及其相关性状的QTL分析

以小麦DH群体(旱选10号×鲁麦14)为研究材料,采用复合区间作图法,对小麦幼苗在水分胁迫及非胁迫条件下的水分利用效率(WUE)及其相关性状的QTL进行定位,并对比分析QTL的加性效应.两种水分条件下共检测到14个具显著加性效应的QTL,分布在2A、3A、4A、5A、6A、7A、1B、3B、3D染色体上,可解释表型变异的范围在6.36%～19.73%.其中,非胁迫(对照)条件下检测到10个QTL,包括2个单株WUE的QTL,5个地上部WUE的QTL,1个根系WUE的QTL及2个总耗水量的QTL;水分胁迫条件下上述性状各检测到1个QTL.对于同一性状没有检测到在两种水分条件下均位于同一标记区间的QTL,表明不同水分环境条件下同一性状的QTL表达模式是不同的.论文也讨论了可能用于标记辅助选择的QTL及其分子标记.     

不同抗旱性冬小麦根系时空分布与产量的关系

为明确不同抗旱性冬小麦品种(Triticum aestivum L.)根系时空分布及其与产量的关系,以抗旱性品种长武134、长旱58和干旱敏感性品种小偃22、西农979为材料,采用根箱试验研究干旱胁迫和充分供水条件下4个品种在拔节期、开花期和成熟期根系总生物量、总根长密度、根系在表层(0—20 cm)和深层(20 cm以下)土壤中的垂直分布、动态变化及其对产量的影响。结果表明,干旱胁迫下抗旱性品种产量显著高于干旱敏感性品种,其中长旱58产量最高,西农979最低;充分供水条件下,西农979产量最高,长武134最低,长旱58与小偃22之间没有差异。相关分析表明,产量与各生育时期根系性状均有显著关系。多元逐步回归分析的结果显示,干旱胁迫和充分供水条件下,拔节期深层根生物量对产量有正效应,而成熟期总根长密度对产量表现为负效应。通径分析表明,干旱胁迫下,根系性状对产量的直接贡献大小为开花期总根长密度(|0.54|)拔节期深层根生物量(|0.36|)成熟期总根长密度(|-0.31|);充分供水时,成熟期总根长密度(|-1.56|)拔节期深层根生物量(|0.83|)。研究表明,减少成熟期总根长密度,增加拔节期深层根生物量对抗旱性及干旱敏感性冬小麦品种产量均有显著的正效应,增加开花期根长密度有利于提高抗旱性冬小麦产量。     

水稻加工品质数量性状基因座 (QTLs)分子定位研究

检测了Lemont/特青RI群体212个株系的糙米率（BR）,精米率（MR）和整精米率（HR）等3项加工品质性状,利用RFLP连锁图和线性模型的复合区间作图方法（QTLMapperV1.0)进行QTL定位研究。群体呈边境分布,双向超亲现象明显,HR较BR,MR变异范围更大并偏向低值方向;分别检测到1个MR,4个HR主效QTL,其中QHr6和QHr7等2个基因座具有较大遗传效应;分别检测到12对影响BR、5对影响MR,16对影响HR的上位性基因座,上位性效应的影响大于主效QTLs,不同性状或同一性状上位性效应通过共同的区间形成复杂的互相联系。     

QTLs and Candidate Genes for Rice Root Growth Under Flooding and Upland Conditions

To investigate the genetic factors underlying constitutive and adaptive root growth under different water-supply conditions, a double haploid (DH) population, derived from a cross between lowland rice variety IR64 and upland rice variety Azucena, with 284 molecular markers was used in cylindrical pot experiments. Several QTLs for seminal root length (SRL), adventitious root number (ARN) and total root dry weight (RW) respectively, under both flooding and upland conditions were detected. Two identical QTLs for SRL and RW were found under flooding and upland conditions. The relative parameters defined as the ratio of parameters under the two water-supply conditions were also used for QTL analysis. A comparative analysis among different genetic populations was performed for the QTLs for root traits and several consistent QTLs for root traits across genetic backgrounds were detected. Candidate genes for cell expansion and elongation were used for comparative mapping with the detected QTLs. Four cell wall-related expressed sequence tags (ESTs) for OsEXP2, OsEXP4, EXT and Xet were mapped on the intervals carrying the QTLs for root traits.     

Mapping QTLs and candidate genes for rice root traits under different water-supply conditions and comparative analysis across three populations

To investigate the genetic factors underlying constitutive and adaptive morphological traits of roots under different water-supply conditions, a recombinant inbred line (RIL) population derived from a cross between the lowland rice variety IR1552 and the upland rice variety Azucena with 249 molecular markers, was used in cylindrical-pot experiments. Eighteen QTLs were detected for seminal root length (SRL), adventitious root number (ARN), and lateral root length (LRL) and lateral root number (LRN) on the seminal root at a soil depth of from 3 to 6 cm under flooding and upland conditions. One identical QTL was detected under both flooding and upland conditions. The relative parameters under the two water-supply conditions were also used for QTL analysis. Five QTLs for upland induced variations in the traits were detected with the positive alleles from Azucena. A comparative analysis was performed for the QTLs detected in this study and those reported from two other populations with Azucena as a parent. Several identical QTLs for root elongation were found across the three populations with positive alleles from Azucena. Candidate genes were screened from ESTs and cDNA-AFLP clones for comparative mapping with the detected QTLs. Two genes for cell expansion, OsEXP2 and endo-1,4--D-glucanase EGase, and four cDNA-AFLP clones from root tissues of Azucena, were mapped on the intervals carrying the QTLs for SRL and LRL under upland conditions, respectively.Communicated by H.C. Becker     

Comparison of QTLs for rice seedling morphology under different water supply conditions

The variation of seedling characteristics under different water supply conditions is strongly associated with drought resistance in rice (Oryza sativa L.) and a better elucidation of its genetics is helpful for improving rice drought resistance. Ninety-six doubled-haploid (DH)rice lines of an indica and japonica cross were grown in both flooding and upland conditions and QTLs for morphological traits at seedling stage were examined using 208 restriction fragment length polymorphism (RFLP) and 76 microsatellite (SSR) markers. A total of 32 putative QTLs were associated with the four seedling traits: average of three adventitious root lengths (ARL), shoot height (SH), shoot biomass (SW), and root to shoot dry weight ratio (RSR). Five QTLs detected were the same under control and upland conditions. The ratio between the mean value of the seedling trait under upland and flooding conditions was used for assessing drought tolerance. A total of six QTLs for drought tolerance were detected. Comparative analysis was performed for the QTLs detected in this case and those reported from two other populations with the same upland rice variety Azucena as parent. Several identical QTLs for seedling elongation across the three populations with the positive alleles from the upland rice Azucena were detected, which suggests that the alleles of Azucena might be involved in water stress-accelerated elongation of rice under different genetic backgrounds. Five cell wall-related candidate genes for OsEXP1, OsEXP2, OsEXP4, EXT, and EGase were mapped on the intervals carrying the QTLs for seedling traits.     

QTLs and epistasis for seminal root length under a different water supply in rice (Oryza sativa L.)

To identify the genetic background of seminal root length under different water-supply conditions, a recombinant inbred (RI) population consisting of 150 lines, derived from a cross between an indica lowland rice, IR1552, and a tropical japonica upland rice, Azucena, was used in both solution culture (lowland condition) and paper culture (upland condition). Quantitative trait loci (QTLs) and epistatic loci for seminal root length were analyzed using 103 restriction fragment length polymorphism (RFLP) markers and 104 amplified fragment length polymorphism (AFLP) markers mapped on 12 chromosomes based on the RI population. One QTL for seminal root length in solution culture (SRLS) and one for seminal root length in paper culture (SRLP) were detected on chromosomes 8 and 1, and about 11% and 10% of total phenotypic variation were explained, respectively. The QTL for SRLP on chromosome 1 was very similar with the QTL for the longest nodal root referred to in a previous report; this QTL may be phenotypically selectable in a breeding program using paper culture. Five pairs of epistatic loci for SRLS were detected, but only one for SRLP, which accounted for about 60% and 20% of the total variation in SRLS and SRLP, respectively. The results indicate that epistasis is a major genetic basis for seminal root length, and there is a different genetic system responsible for seminal root growth under different water supply conditions. Received: 26 May 2000 / Accepted: 19 October 2000     

QTL mapping of root traits in a doubled haploid population from a cross between upland and lowland japonica rice in three environments

To genetically dissect drought resistance associated with japonica upland rice, we evaluated a doubled haploid (DH) population from a cross between two japonica cultivars for seven root traits under three different growing conditions (upland, lowland and upland in PVC pipe). The traits included basal root thickness (BRT), total root number (RN), maximum root length (MRL), root fresh weight (RFW), root dry weight (RDW), ratio of root fresh weight to shoot fresh weight (RFW/SFW) and ratio of root dry weight to shoot dry weight (RDW/SDW). The BRT was significantly correlated with the index of drought resistance, which was defined as the ratio of yield under the stress of the upland condition to that under the normal lowland condition. A complete genetic linkage map with 165 molecular markers covering 1,535 cM was constructed. Seven additive quantitative trait loci (QTLs) and 15 pairs of epistatic loci for BRT and RN were identified under upland and lowland conditions, and 12 additive QTLs and 17 pairs of epistatic QTLs for BRT, RN, MRL, RFW, RFW/SFW and RDW/SDW were identified under the PVC pipe condition. Four additive QTLs and one pair of epistatic QTLs controlling IDR were also found. These QTLs individually explained up to 25.6% of the phenotypic variance. QTL × environment (Q × E) interactions were detected for all root traits, and the contributions of these interactions ranged from 1.1% to 19.9%. Five co-localized QTLs controlling RFW and RDW, RFW/SFW, RDW/SDW and IDR, BRT and RN, RN, MRL and IDR were found. Four types of QTLs governing BRT and RN were classified by their detection in the upland and lowland conditions. Some common QTLs for root traits across different backgrounds were also revealed. These co-localized QTLs and common QTLs will facilitate marker-assisted selection for root traits in rice breeding programs.     

QTLs associated with root traits increase yield in upland rice when transferred through marker-assisted selection

Altering root morphology of rice (Oryza sativa L.) cultivars could improve yields in drought-prone upland ecosystems. Marker-assisted backcross breeding was used to introgress four QTLs for root traits into an upland rice cultivar. The QTLs had previously been identified under experimental conditions in a different genetic background. The introgressed lines and the recurrent parent were grown for 6 years by resource-poor farmers in upland sites in Eastern India and yields recorded. In combination the QTLs significantly increased yield by 1 t ha^?1 under relatively favourable field conditions. In less favourable trials, the QTL effects were not detected due to greater heterogeneity in soil–water availability in very low yielding environments and consequent yield variability. Root studies under controlled conditions showed that lines with the introgressions had longer roots throughout tillering than the recurrent parent (14 cm longer 2 weeks after sowing). Therefore, both improved roots and increased yield can be attributed to the introgression of QTLs. This is the first demonstration that marker-assisted backcross breeding (MABC) to introgress multiple root QTLs identified under controlled conditions is an effective strategy to improve farmers’ yields of upland rice. The strategy was used to breed a novel upland rice cultivar that has been released in India as Birsa Vikas Dhan 111.     

Mapping QTLs for root traits in a recombinant inbred population from two indica ecotypes in rice

Evaluation of root traits in rainfed lowland rice is very difficult. Molecular genetic markers could be used as an alternative strategy to phenotypic selection for the improvement of rice root traits. This research was undertaken to map QTLs associated with five root traits using RFLP and AFLP markers. Recombinant inbred lines (RILs) were developed from two indica parents, IR58821–23-B-1–2-1 and IR52561-UBN-1–1-2, that were adapted to rainfed lowland production systems. Using wax-petrolatum layers to simulate a hardpan in the soil, 166 RILs were evaluated for total root number (TRN), penetrated root number (PRN), root penetration index (RPI, the ratio of PRN to TRN), penetrated root thickness (PRT) and penetrated root length (PRL) under greenhouse conditions during the summer and the fall of 1997. A genetic linkage map of 2022 cM length was constructed comprising 303 AFLP and 96 RFLP markers with an average marker space of 5.0 cM. QTL analysis via interval mapping detected 28 QTLs for these five root traits, which were located on chromosomes 1, 2, 3, 4, 6, 7, 10 and 11. Individual QTLs accounted for between 6 and 27% of the phenotypic variation. Most of the favorable alleles were derived from the parent IR58821–23-B-1–2-1, which was phenotypically superior in root traits related to drought resistance. Three out of six QTLs for RPI were detected in both summer and fall experiments and they also were associated with PRN in both experiments. Out of eight QTLs for RPT, five were common in both seasons. Two genomic regions on chromosome 2 were associated with three root traits (PRN, PRT and RPI), whereas three genomic regions on chromosomes 2 and 3 were associated with two root traits (PRT and RPI). Two QTLs affecting RPI and two QTLs affecting PRT were also found in similar genomic regions in other rice populations. The consistent QTLs across genetic backgrounds and the common QTLs detected in both experiments should be good candidates for marker-assisted selection toward the incorporation of root traits in a drought resistance breeding program, especially for rainfed lowland rice. Received: 17 November 1999 / Accepted: 19 March 2000     

Mapping QTLs of root morphological traits at different growth stages in rice

Roots are a vital organ for absorbing soil moisture and nutrients and influence drought resistance. The identification of quantitative trait loci (QTLs) with molecular markers may allow the estimation of parameters of genetic architecture and improve root traits by molecular marker-assisted selection (MAS). A mapping population of 120 recombinant inbred lines (RILs) derived from a cross between japonica upland rice 'IRAT109' and paddy rice 'Yuefu' was used for mapping QTLs of developmental root traits. All plant material was grown in PVC-pipe. Basal root thickness (BRT), root number (RN), maximum root length (MRL), root fresh weight (RFW), root dry weight (RDW) and root volume (RV) were phenotyped at the seedling (I), tillering (II), heading (III), grain filling (IV) and mature (V) stages, respectively. Phenotypic correlations showed that BRT was positively correlated to MRL at the majority of stages, but not correlated with RN. MRL was not correlated to RN except at the seedling stage. BRT, MRL and RN were positively correlated to RFW, RDW and RV at all growth stages. QTL analysis was performed using QTLMapper 1.6 to partition the genetic components into additive-effect QTLs, epistatic QTLs and QTL-by-year interactions (Q x E) effect. The results indicated that the additive effects played a major role for BRT, RN and MRL, while for RFW, RDW and RV the epistatic effects showed an important action and Q x E effect also played important roles in controlling root traits. A total of 84 additive-effect QTLs and 86 pairs of epistatic QTLs were detected for the six root traits at five stages. Only 12 additive QTLs were expressed in at least two stages. This indicated that the majority of QTLs were developmental stage specific. Two main effect QTLs, brt9a and brt9b, were detected at the heading stage and explained 19% and 10% of the total phenotypic variation in BRT without any influence from the environment. These QTLs can be used in breeding programs for improving root traits.     

Genetic analysis for drought resistance of rice at reproductive stage in field with different types of soil

Drought resistance of rice is a complex trait and is mainly determined by mechanisms of drought avoidance and drought tolerance. The present study was conducted to characterize the genetic basis of drought resistance at reproductive stage in field by analyzing the QTLs for drought response index (DRI, normalized by potential yield and flowering time), relative yield, relative spikelet fertility, and four traits of plant water status and their relationships with root traits using a recombinant inbred population derived from a cross between an indica rice and upland rice. A total of 39 QTLs for these traits were detected with individual QTL explained 5.1–32.1% of phenotypic variation. Only two QTLs for plant water status were commonly detected in two environments, suggesting different mechanisms might exist in two types of soil conditions. DRI has no correlation with potential yield and flowering time under control, suggesting that it can be used as a good drought resistance index in field conditions. The co-location of QTLs for canopy temperature and delaying in flowering time suggested a usefulness of these two traits as indexes in drought resistance screening. Correlation and QTL congruence between root traits and putative drought tolerance traits revealed that drought avoidance (via thick and deep root traits) was the main genetic basis of drought resistance in sandy soil condition, while drought tolerance may play more role in the genetic basis of drought resistance in paddy soil condition. Therefore, both drought mechanisms and soil textures must be considered in the improvement of drought resistance at reproductive stage in rice.