水稻灌浆期耐热害的数量性状基因位点分析

 利用由98个家系组成的Nipponbare / Kasalath // Nipponbare回交重组自交系群体及其分子连锁图谱，以粒重感热指数\[（适温粒重-高温粒重）/适温粒重×100\]为评价指标，采用混合线性模型的QTL定位方法，对水稻灌浆期耐热性的主效、上位性数量性状基因位点及其与环境的互作进行分析。共检测到3个灌浆期耐热性主效QTL，分别位于第1、4和7染色体上，LOD值为8.16、11.08和12.86，贡献率8.94%、17.25%和13.50%。其中位于第4染色体标记C1100-R1783之间的QTL，没有显著的上位性和环境互作效应，表明在不同环境和遗传背景中的表达较为稳定，在水稻耐热性育种中可能具有较大的利用价值，其耐热性等位基因来自亲本Kasalath，高温热害时可减少粒重损失3.31%。位于第1染色体标记R1613-C970之间的QTL和第7染色体标记C1226-R1440之间的QTL，耐热性等位基因来自亲本Nipponbare，分别可减少粒重损失2.38%和2.92%。这两个QTL均具有与环境的互作效应，其中第7染色体上的QTL还和其他基因位点有互作。检测到8对加性×加性上位性互作QTL，分布于第1、2、3、5、7、8、10和12染色体上。没有检测到上位性QTL与环境的互作效应。     

Confirmation of Novel Quantitative Trait Loci for Seed Dormancy at Different Ripening Stages in Rice

Seed dormancy contributes resistance to pre-harvest sprouting.Effects on respective quantitative trait loci (QTLs) for dormancy should be assessed by using fresh seeds before germinability altered through storage.We investigated QTLs related to seed dormancy using backcross inbred lines derived from a cross between Nipponbare and Kasalath.Four putative QTLs for seed dormancy were detected immediately after harvest using composite interval mapping.These putative QTLs were mapped near C1488 on chromosome 3 (qSD-3.1),R2171 on chromosome 6 (qSD-6.1),R1245 on chromosome 7 (qSD-7.1) and C488 on chromosome 10 (qSD-10.1).Kasalath alleles promoted dormancy for qSD-3.1,qSD-6.1 and qSD-7.1,and the respective proportions of phenotypic variation explained by each QTL were 12.9%,9.3% and 8.1%.We evaluated the seed dormancy harvested at different ripening stages during seed development using chromosome segment substitution lines (CSSLs) to confirm gene effects.The germination rates of CSSL27 and CSSL28 substituted with the region including qSD-6.1 were significantly lower than those of Nipponbare and other CSSLs at the late ripening stage.Therefore,qSD-6.1 is considered the most effective novel QTL for pre-harvest sprouting resistance among the QTLs detected in this study.     

Mapping QTL for Heat-Tolerance at Grain Filling Stage in Rice

A mapping population of 98 lines (backcross inbred lines, BILs) derived from a backcross of Nipponbare/Kasalath// Nipponbare was planted at two experimental sites, Nanjing and Nanchang, and treated with high and optimal temperature during grain filling, respectively. The grain weight heat susceptibility index [GWHSI= (grain weight at optimum temperature-grain weight at high temperature) / grain weight at optimum temperature ×100] was employed to evaluate the tolerance of rice to heat stress. A genetic linkage map with 245 RFLP markers and a mixed linear-model approach was used to detect quantitative trait loci (QTLs) and their main effects, epistatic interactions and QTL×environment interactions (Q×E). The threshold of LOD score=2.0 was used to detect the significance of association between marker and trait. A total of 3 QTLs controlling heat tolerance during grain filling were detected, on chromosomes 1, 4 and 7, with LOD scores of 8.16, 11.08 and 12.86, respectively, and they explained the phenotypic variance of 8.94, 17.25 and 13.50 %, correspondingly. The QTL located in the C1100-R1783 region of chromosome 4 showed no QTL×environment interaction and epistatic effect, suggesting that it could be stably expressed in different environments and genetic backgrounds, and thus it would be valuable in rice breeding for heat tolerance improvement. This QTL allele, derived from Kasalath reduced 3.31% of the grain weight loss under heat stress. One located between R1613-C970 on chromosome 1 and the other between C1226-R1440 on chromosome 7, with additive effect 2.38 and 2.92%, respectively. The tolerance alleles of both these QTLs were derived from Nipponbare. Both of these QTLs had significant QTL×environment interactions, and the latter was involved in epistatic interaction also. Eight pairs of epistatic effect QTLs were detected, one pair each on chromosomes 1,2,3, 5, 7, 8, 10 and 12. The results could be useful for elucidating the genetic mechanism of heat-tolerance and the development of new rice varieties with heat tolerance during grain filling phase.     

稻米直链淀粉含量和胶稠度对高温耐性的QTL分析

利用由98个家系组成的Nipponbare/Kasalath//Nipponbare回交重组自交系群体,以直链淀粉含量耐热指数（高温下直链淀粉含量/适温下直链淀粉含量×100）和胶稠度耐热指数（高温下胶稠度/适温下胶稠度×100）为评价指标,采用混合线性模型的QTL定位方法,在南昌和南京两个试验地点对水稻蒸煮食用品质性状的高温耐性QTL进行了检测。两个性状在两个试验地点共检测到9个QTLs,其中直链淀粉含量高温耐性QTL 3个,胶稠度高温耐性QTL 6个。两个性状中共有3个QTLs在两个地点同时被检测到。其中位于第6染色体上与Wx基因相同的染色体区域和第8染色体G1073-R727区域分别是控制直链淀粉含量和胶稠度高温耐性的重要区域。     

利用回交重组自交系定位稻米赖氨酸含量的基因座位

利用日本晴（粳稻）/Kasalath（籼稻）//日本晴组合衍生的98个回交重组自交系（BILs）株系和具有245个RFLP标记的遗传图谱,在浙江和海南2个环境条件下,开展了精米赖氨酸含量的QTL定位。精米赖氨酸含量在浙江和海南均表现连续变异和超亲分离。在第6染色体发现2个具有显著遗传主效应的QTL(qLYS6 1和qLYS6 2）,表型贡献率分别为2708%和4756%。qLYS6 1 还具有显著的环境互作效应。qLYS6 1的增效基因来自Kasalath,而qLYS6 2的增效基因来自日本晴。未检测到显著的上位性效应。     

Mapping Quantitative Trait Loci for Palatability of Milled Rice

Quantitative trait loci (QTLs) controlling palatability in rice were identified using a set of 98 backcross inbred lines (BILs) population derived from a cross between a japonica variety Nipponbare and an indica variety Kasalath. The palatability scores of the population measured by RQ1/Plus Rice Analyzer, showed a continuous and transgressive segregative distribution with a range from 66 to 92. Four putative QTLs for palatability, qPAL-5, qPAL-7, qPAL-8a and qPAL-8b, were detected on chromosome 5, 7 and 8, and they accounted 7.83, 7.03, 11.58 and 7.19% of the total phenotypic variation, respectively. Three alleles qPAL-5, qPAL-7 and qPAL-8b from Kasalath increased the palatability score, whereas only one Nipponbare allele qPAL-8a increased the score. Eight transgressive lines in palatability were selected to make a comparison between phenotypic and genotypic classes. The result explained the possibility of positive QTLs pyramiding through marker-assisted selection of highly palatable rice.     

Characterizing the Saltol Quantitative Trait Locus for Salinity Tolerance in Rice

This study characterized Pokkali-derived quantitative trait loci (QTLs) for seedling stage salinity tolerance in preparation for use in marker-assisted breeding. An analysis of 100 SSR markers on 140 IR29/Pokkali recombinant inbred lines (RILs) confirmed the location of the Saltol QTL on chromosome 1 and identified additional QTLs associated with tolerance. Analysis of a series of backcross lines and near-isogenic lines (NILs) developed to better characterize the effect of the Saltol locus revealed that Saltol mainly acted to control shoot Na⁺/K⁺ homeostasis. Multiple QTLs were required to acquire a high level of tolerance. Unexpectedly, multiple Pokkali alleles at Saltol were detected within the RIL population and between backcross lines, and representative lines were compared with seven Pokkali accessions to better characterize this allelic variation. Thus, while the Saltol locus presents a complex scenario, it provides an opportunity for marker-assisted backcrossing to improve salt tolerance of popular varieties followed by targeting multiple loci through QTL pyramiding for areas with higher salt stress.     

Genetic relationship between grain chalkiness,protein content,and paste viscosity properties in a backcross inbred population of rice

A backcross inbred line population derived from a cross between Koshihikari and Kasalath was used to dissect the genetic relationship among chalkiness, protein content, and paste viscosity properties in rice in three environments. A total of 11 traits (or parameters) were analyzed, including percentage of grains with chalkiness (PGWC), protein content (PC) and protein index (PI), and eight parameters from the viscosity profile. PGWC, PC and PI were significantly correlated with the paste viscosity parameters. We identified 39 QTLs in three environments; ten QTL clusters emerged. Eight QTLs were consistently detected across the three environments and further confirmed using a set of chromosome segment substitution lines (CSSLs) where Kasalath was used as the donor parent and Koshihikari as the recurrent parent. One and two major clusters on chromosome 6 corresponded to the Wx and Alk loci, respectively. The former was responsible for PGWC and most of the viscosity parameters, and the latter for PI and some viscosity parameters. Particularly, QTL qPI-6.1 was linked with both the Wx and Alk loci. The co-locations of QTLs for PGWC and viscosity parameters and the linkage of qPI-6.1 and qBDV-6 at the Wx locus could be largely responsible for the phenotypic correlations between these traits.     

Identification of QTLs for Improvement of Plant Type in Rice (Oryza sativa L.) Using Koshihikari / Kasalath Chromosome Segment Substitution Lines and Backcross Progeny F2 Population

Abstract

Thirty-nine chromosome segment substitution lines (CSSLs) population derived from a Koshihikari / Kasalath cross was used for quantitative trait locus (QTL) analysis of plant type in rice (Oryza sativa L.). Putative rough QTLs (26.2～60.3cM of Kasalath chromosomal segments) for culm length, plant height, panicle number, chlorophyll content of flag leaf blade at heading and specific leaf weight, were mapped on the several chromosomal segments based on the comparison of CSSLs with Koshihikari in the field experiment for 3 years. In order to verify and narrow QTLs detected in CSSLs, we conducted QTL analyses using F₂ populations derived from a cross between Koshihikari and target CSSL holding a putative rough QTL. The qPN-2, QTL for panicle number was mapped on chromosome 2. In traits of flag leaf, the qCHL-4-1 and qCHL-4-2 for chlorophyll content was mapped on chromosome 4, and the qSLW-7 for specific leaf weight on chromosome 7. All QTLs were detected in narrow marker intervals, compared with rough QTLs in CSSLs. The qPN-2, qCHL-4-1 and qCHL-4-2 had only additive effect. On the other hand, the qSLW-7 showed over-dominance. It could be emphasized that QTL analysis in the present study with the combination of CSSLs and backcross progeny F₂ population can not only verify the rough QTLs detected in CSSLs but also estimate allelic effects on the QTL.     

稻米垩白性状对高温耐性的QTL分析

【目的】本研究旨在筛选与稻米外观品质高温耐性连锁的分子标记,为稻米品质育种提供参考。【方法】以耐热水稻品系996和热敏感水稻品系4628为亲本构建的重组自交系为材料,采用垩白粒率耐热指数、垩白大小耐热指数和垩白度耐热指数为评价指标,对水稻垩白性状的高温耐性QTL进行检测。【结果】采用复合区间作图法两年共检测到垩白性状高温耐性QTL 24个,包括垩白粒率高温耐性QTL 8个,垩白大小高温耐性QTL 12个,垩白度高温耐性QTL 4个。其中,第6染色体上的2个垩白粒率高温耐性QTL和第7染色体上的2个垩白度高温耐性QTL在两年中重复检测到,且这2个稳定表达的垩白度位点与2015年检测到的第7染色体上的垩白粒率位点重合。另外,发现有4个QTL一因多效,同时影响垩白粒率、垩白大小及垩白度。【结论】控制垩白粒率耐热指数的q HTCGR6.1和控制垩白度耐热指数的q HTCD7.1是新的QTL。     

Identification and validation of a novel major QTL for harvest index in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Background

Harvest index (HI) in rice is defined as the ratio of grain yield (GY) to biomass (BM). Although it has been demonstrated that HI is significantly related to yield and is considered as one of the most important traits in high-yielding rice breeding, HI-based high-yielding rice breeding is difficult due to its polygenic nature and insufficient knowledge on the genetic basis of HI. Therefore, searching for rice varieties with high HI and mapping genes associated with high HI can facilitate marker-assisted breeding for high HI in rice.

Results

Yuexiangzhan, a popular indica cultivar with good reputation of high HI was crossed with Shengbasimiao, an indica cultivar with lower HI to develop a recombinant inbred line population, and QTL mapping for HI and its component traits was conducted. In total, five QTLs for HI, three QTLs for GY, and six QTLs for BM were detected in two-year experiments. Among the three GY QTLs, one co-located with the HI QTL on chromosome 8, while the other two co-located with the two tightly-linked BM QTLs on chromosome 3. The co-located QTLs in each of the chromosomal regions produced additive effects in the same direction. Particularly, the HI QTL on chromosome 8, qHI-8, could be detected across two years and explained 42.8% and 44.5% of the phenotypic variation, respectively. The existence of qHI-8 was confirmed by the evaluation of the near isogenic lines derived from a residual heterozygous line, and this QTL was delimitated to a 1070 kb interval by substitution mapping.

Conclusion

In the present study, the detected GY QTLs overlapped with both HI QTL and BM QTL, suggesting a positive relationship between GY and HI or BM, respectively. With an understanding of the genetic basis for grain yield, harvest index and biomass, it is possible to achieve higher yield through enhancing HI and BM by pyramiding the favorable alleles for the two traits via marker-assisted selection (MAS). As qHI-8 has a large phenotypic effect on HI and expresses stably in different environments, it provides a promising target for further genetic characterization of HI and MAS of high HI in rice breeding.

     

QTL Analysis of Anoxic Tolerance at Seedling Stage in Rice

Coleoptile lengths of 7-day-old seedlings under anoxic stress and normal conditions were investigated in two permanently segregated populations and their parents in rice (Oryza sativa L.). Using anoxic response index, a ratio of coleoptile length under anoxic stress to coleoptile length under normal conditions, as an indicator of seedling anoxic tolerance (SAT), QTLs for SAT were detected. Two loci controlling SAT, designated as qSAT-2-R and qSAT-7-R, were detected in a recombinant inbred line (RIL) population (247 lines) derived from a cross between Xiushui 79 (japonica variety) and C Bao (japonica restorer line). qSAT-2-R, explaining 8.7% of the phenotype variation, was tightly linked with the SSR marker RM525. qSAT-7-R, explaining 9.8% of the phenotype variation, was tightly linked with the marker RM418. The positive alleles of the two loci came from C Bao. Six loci controlling SAT, designated as qSAT-2-B, qSAT-3-B, qSAT-5-B, qSAT-8-B, qSAT-9-B and qSAT-12-B, were detected in a backcross inbred line (BIL) population (98 lines) derived from a backcross of Nipponbare (japonica)/Kasalath (indica)//Nipponbare (japonica). The positive alleles of qSAT-2-B, qSAT-3-B and qSAT-9-B, which explained 16.2%, 11.4% and 9.5% of the phenotype variation, respectively, came from Nipponbare. Besides, the positive alleles of qSAT-5-B, qSAT-8-B and qSAT-12-B, which explained 7.3%, 5.8% and 14.0% of the phenotype variation, respectively, were from Kasalath.     

特大粒水稻材料粒型性状的QTL检测

 利用特大粒粳稻TD70（2011年千粒重达80 g）和籼稻品种Kasalath杂交,经单粒传法获得的240个重组自交系（RIL）为作图群体,分别于2010年和2011年对粒长、粒宽、粒厚性状进行鉴定,用完备区间作图法,以均匀分布于12条染色体的141个SSR标记对粒型性状进行QTL检测。共检测到粒型性状的 QTL 18 个,分布于第2、3、5、7、9和12染色体上。其中,控制粒长的QTL 5个,控制粒宽的QTL 6个,控制粒厚的QTL 7个。两年间均能检测到的QTL有7个,分别为粒长QTL qGL3.1,粒宽QTL qGW2.1、qGW2.2、qGW5.1、qGW5.2,粒厚QTL qGT2.3、qGT3.1;其平均贡献率分别为56.19%、4.42%、29.41%、10.37%、7.61%、21.19%和17.06%。第2染色体RM1347-RM5699区间是粒长、粒宽、粒厚的共同标记区间。第3染色体RM6080-RM6832区间为粒长qGL3.1、粒厚qGT3.1共同标记区间。18 个QTL的增效等位基因均来源于大粒亲本TD70,且增效作用显著。定位的大部分位点包含已报道的精细定位和克隆的主要粒型基因;除第2染色体的qGW2.1（qGT2.1）、qGW2.3、qGL2.2和第12染色体的qGT12等位点已有粒型性状相关报道外,定位的qGT22,qGW9 和qGT9可能是新的QTL。     

Identification of QTLs for Cooking and Eating Quality of Rice Grain

Rice is one of the major crops served as the staple food of more than 50% of the world’s population. Recently, more attention has been paid to rice quality, especially the cooking and eating quality than achieving the higher yield. The amylose content (AC), gelatinization temperature (GT) and gel consistency (GC) are the three major rice characteristics directly related to cooking and eating quality, responsible for the physical and chemical characteristics of the starch in the endosperm [1…     

Mapping QTLs using a novel source of salinity tolerance from Hasawi and their interaction with environments in rice

Background

Salinity is one of the most severe and widespread abiotic stresses that affect rice production. The identification of major-effect quantitative trait loci (QTLs) for traits related to salinity tolerance and understanding of QTL × environment interactions (QEIs) can help in more precise and faster development of salinity-tolerant rice varieties through marker-assisted breeding. Recombinant inbred lines (RILs) derived from IR29/Hasawi (a novel source of salinity) were screened for salinity tolerance in the IRRI phytotron in the Philippines (E1) and in two other diverse environments in Senegal (E2) and Tanzania (E3). QTLs were mapped for traits related to salinity tolerance at the seedling stage.

Results

The RILs were genotyped using 194 polymorphic SNPs (single nucleotide polymorphisms). After removing segregation distortion markers (SDM), a total of 145 and 135 SNPs were used to construct a genetic linkage map with a length of 1655 and 1662 cM, with an average marker density of 11.4 cM in E1 and 12.3 cM in E2 and E3, respectively. A total of 34 QTLs were identified on 10 chromosomes for five traits using ICIM-ADD and segregation distortion locus (SDL) mapping (IM-ADD) under salinity stress across environments. Eight major genomic regions on chromosome 1 between 170 and 175 cM (qSES1.3, qSES1.4, qSL1.2, qSL1.3, qRL1.1, qRL1.2, qFWsht1.2, qDWsht1.2), chromosome 4 at 32 cM (qSES4.1, qFWsht4.2, qDWsht4.2), chromosome 6 at 115 cM (qFWsht6.1, qDWsht6.1), chromosome 8 at 105 cM (qFWsht8.1, qDWsht8.1), and chromosome 12 at 78 cM (qFWsht12.1, qDWsht12.1) have co-localized QTLs for the multiple traits that might be governing seedling stage salinity tolerance through multiple traits in different phenotyping environments, thus suggesting these as hot spots for tolerance of salinity. Forty-nine and 30 significant pair-wise epistatic interactions were detected between QTL-linked and QTL-unlinked regions using single-environment and multi-environment analyses.

Conclusions

The identification of genomic regions for salinity tolerance in the RILs showed that Hasawi possesses alleles that are novel for salinity tolerance. The common regions for the multiple QTLs across environments as co-localized regions on chromosomes 1, 4, 6, 8, and 12 could be due to linkage or pleiotropic effect, which might be helpful for multiple QTL introgression for marker-assisted breeding programs to improve the salinity tolerance of adaptive and popular but otherwise salinity-sensitive rice varieties.

     

Molecular mapping of quantitative trait loci for zinc toxicity tolerance in rice seedling (Oryza sativa L.)

Excess zinc harms the growth of rice plants and zinc toxicity can easily occur in acid soils. The aim of the study was to map quantitative trait loci (QTLs) in rice for tolerance to zinc toxicity, using a recombinant inbred (RI) population derived from the cross of a japonica variety (Asominori: relatively tolerant to Zn²⁺ toxicity) with an indica variety (IR24, relatively susceptible), through 289 RFLP markers. The index scores of damage (representing Zn²⁺ toxicity tolerance), after irrigating rice seedlings with a 1000-ppm Zn²⁺ solution for 20 successive days, were examined for each RI line and its parental varieties. Continuous distributions and transgressive segregations of the index scores were observed in the RI population, suggesting that Zn²⁺ toxicity tolerance was a quantitatively inherited trait. Three QTLs for Zn²⁺ toxicity tolerance were detected on chromosomes 1, 3 and 10 and explained 21.9, 8.9 and 7.6%, respectively, of the total phenotypic variation. The results and the tightly linked molecular markers that flank the QTLs, detected in this study, will be useful in improving Zn²⁺ tolerance in rice. In addition, the genomic positions between QTLs for Zn²⁺ toxicity tolerance and the QTLs for other metal (Fe²⁺, Mn²⁺, Al³⁺) toxicity tolerances, from previous studies, are discussed.     

QTL analysis of panicle morphology response to irrigation regime in aerobic rice culture

In water-efficient rice production, grain yield is often constrained by panicle size. The objective of this study was to genetically dissect the response of panicle morphology to irrigation regimes in aerobic rice culture. We grew ‘Akihikari’ (a lowland japonica cultivar) × ‘IRAT109’ (an upland japonica cultivar) backcross inbred lines in aerobic soils with full or limited irrigation for 2 years, and examined 4 panicle traits—number of florets per panicle (FPP), number of primary branches per panicle (BPP), number of florets per primary branch (FPB), and frequency of pre-flowering floret abortion (%FA)—and grain yield. QTLs for BPP were detected in both the irrigation regimes but QTLs for FPB and %FA were detected mostly only in either of the irrigation regimes. The QTL for FPP on chromosome 2 (RM3421–RM213) coincided with that for yield under full irrigation, showing that this QTL is related to sink capacity and yield potential in aerobic rice culture. On the other hand, the QTL for FPB on chromosome 1 (RM3148–RM243) coincided with that for yield under limited irrigation, when water deficit was moderate. The QTL for root axis length at vegetative stage, previously identified in the same mapping population, was located near this region. This study unravelled the complicated genetic control on panicle morphology in aerobic rice culture, and suggested the positive roles of the dehydration avoidance mechanism by vigorous root growth on panicle size and yield under dry soil conditions.     

波兰小麦×普通小麦品系“中13”RIL群体籽粒特性的QTL定位

小麦籽粒特性与籽粒产量和品质密切相关。本研究以波兰小麦(Tiriticum polonicum L.)×普通小麦(Triticum aestivum L.)品系"中13"杂交组合衍生的99个F8重组自交系(Recombinant inbred lines,RIL)群体为材料,利用SSR分子标记构建连锁遗传图谱。根据两年实验数据,利用复合区间作图法对粒重、粒长和粒宽3个籽粒特性相关性状进行了QTL定位分析,共检测到12个与籽粒特性相关的加性QTL位点。其中,3个粒重QTL,1个位于1A染色体上,另外2个都在2A染色体上,单个QTL可解释表型变异的13.35%～20.04%;5个粒长QTL,其中2个位于2A染色体上,其余3个分别位于3A、5A和2B染色体上,单个QTL可解释表型变异的8.53%～21.03%;4个粒宽QTL,分别位于1A、2A、3B和5B染色体上,单个QTL可解释表型变异的9.76%～40.79%。在2A染色体上共检测到5个籽粒特性相关性状的QTL,表明2A染色体与籽粒特性关系密切。     

水稻抽穗期基因的精细定位、克隆和生物学功能分析

介绍了水稻抽穗期QTL研究的进展,在相同亲本日本晴/Kasalath衍生的不同类型的多个群体中,共检测到15个QTL;应用高世代回交后代,精细定位了其中8个QTL;将在初步定位时同一区间检测到的1个控制种子休眠期QTL(Sdr1)和1个抽穗期QTL (Hd8),分解为两个紧密连锁的基因;将经过精细定位表明可能具有双重功能的单个孟德尔因子Hd3,分解为两个功能不同的紧密连锁的基因Hd3a和Hd3b;根据QTL近等基因系的光周期反应以及这些座位间上位性互作的研究,明确了其中6个QTL的生物学功能;应用图位法克隆了其中3个QTL,研究了它们的表达和调控,并与拟南芥的同源基因进行比较。为水稻其他数量性状以及其他作物数量性状的遗传学研究,提供了一个范例。     

Identification of QTLs for Cadmium Tolerance During Seedling Stage and Validation of qCDSL1 in Rice

Cadmium(Cd)is a non-essential toxic metal that is harmful to plants.To investigate the genetic mechanism of Cd tolerance in rice,quantitative trait loci(QTLs)associated with Cd tolerance at the seedling stage were analyzed using a recombinant inbred line(RIL)population derived from a cross between PA64s and 93-11.A total of 36 QTLs associated with shoot length,root length,shoot dry weight,root dry weight and total dry weight were detected in Hangzhou and Lingshui of China.Among them,15 QTLs were identified under the control condition and 15 QTLs were identified under the Cd stress condition,and 6 QTLs for Cd tolerant coefficient were detected on chromosomes 1,3,7 and 9.The qCDSL1.1 and qCDSL1.2 were identified in Hangzhou and Lingshui,respectively,and had overlapping intervals on chromosome 1.To further confirm the effects of qCDSL1.1 and qCDSL1.2,we developed a chromosome segment substitution line(CSSL),CSSLqCDSL1,in 93-11 background harboring qCDSL1.1/qCDSL1.2 from PA64s.Compared to 93-11,CSSLqCDSL1 had increased shoot length under the Cd stress condition.These results pave the way for further isolation of those genes controlling Cd tolerance in rice and marker-assistant selection of rice elite varieties with Cd tolerance.