Quantitative Trait Loci for Mercury Tolerance in Rice Seedlings

Mercury （Hg） is one of the most toxic heavy metals to living organisms and its conspicuous effect is the inhibition of root growth. However, little is known about the molecular genetic basis for root growth under excess Hg2＋ stress. To map quantitative trait loci （QTLs） in rice for Hg2＋ tolerance, a population of 120 recombinant inbred lines derived from a cross between two japonica cultivars Yuefu and IRAT109 was grown in 0.5 mmol/L CaCI2 solution. Relative root length （RRL）, percentage of the seminal root length in ＋HgCI2 to -HgCI2, was used for assessing Hg2＋ tolerance. In a dose-response experiment, Yuefu had a higher RRL than IRAT109 and showed the most significant difference at the Hg2＋ concentration of 1.5 tJmol/L. Three putative QTLs for RRL were detected on chromosomes 1, 2 and 5, and totally explained about 35.7% of the phenotypic variance in Hg2＋ tolerance. The identified QTLs for RRL might be useful for improving Hg2＋ tolerance of rice by molecular marker-assisted selection.

Genetic Dissection of Low Phosphorus Tolerance Related Traits Using Selected Introgression Lines in Rice

To dissect the genetic basis of low phosphorus tolerance （LPT）, 114 BC2F4 introgression lines （ILs） were developed from Shuhui 527 and Minghui 86 （recurrent parents）, and Yetuozai （donor parent）. The progenies were tested for 11 quantitative traits under three treatments including normal fertilization in normal soil （as control）, normal fertilization in barren soil and low phosphorus stress in barren soil in Langfang, Hebei Province, China. Moreover, the ILs were investigated at the seedling stage using nutrient solution culture method in greenhouse in Beijing, China. A total of 49 main-effect quantitative trait loci （QTLs） underlying yield related traits were identified in Langfang, and their contributions to phenotypic variations ranged from 6.7% to 16.5%. Among them, 25 （51.0%） QTLs had favorable alleles from donor parent. A total of 48 main-effect QTLs were identified for LPT-related traits in Beijing, and their contributions to phenotypic variations ranged from 7.7% to 16.6%. Among them, 21 （43.8%） QTLs had favorable alleles from donor parent. About 79.6% of the QTLs can be detected repeatedly under two or more treatments, especially QTLs associated with spikelet number per panicle, spikelet fertility and 1000-grain weight, displaying consistent phenotypic effects. Among all the detected QTLs, eight QTLs were simultaneously identified under low phosphorus stress across two environments. These results can provide useful information for the genetic dissection of LPT in rice.

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.

Mapping of QTLs for Leaf Malondialdehyde Content Associated with Stress Tolerance in Rice

Malondialdehyde （MDA） is the final product of lipid peroxidation, and MDA content can reflect the stress tolerance of plants. To map QTLs conditioning the MDA content in rice leaves, a recombinant inbred line （RIL） population with 247 lines derived from an indica-indica cross Zhenshan 97BxMilyang 46, and a linkage map consisting of 207 DNA markers were used. The RIL population showed a transgressive segregation in the MDA content of rice leaves. Two QTLs for the MDA content in rice leaves were detected in the intervals RG532-RG811 and RG381-RG236 on chromosome 1, with the additive effects from maternal and paternal parents, accounting for 4.33% and 4.62% of phenotype variations, respectively.

Inheritance and QTL Mapping of Salt Tolerance in Rice

An F2 population derived from the cross between Jiucaiqing (Japonica) and IR36 (indica) was used to analyze the inheritance of salt tolerance in rice by genetic model of major-genes plus polygenes, and to map the corresponding QTLs by SSR molecular markers. Rice plants of P1, P2, F1 and F2 at 5- to 6- leaf stage were treated under 140 mmol/LNaCI for 10 days. Three indices representing the ability of salt tolerance of rice seedlings were measured, including salt tolerance rating (STR), Na+/K+ ratio in roots and dry matter weight of shoots (DWS). STR, Na+/K+ and DWS were all controlled by two major genes with modification by polygenes. Heritability of these traits from major genes was 17.8, 53.3 and 52.3%, respectively. The linkage map constructed by 62 SSR molecular markers covered a total length of about 1 142 cM. There were three QTLs detected for STR located on chromosome 1, 5 and 9, two QTLs for DWS on chromosomes 8 and 9, and two QTLs for Na+/K+ on chromosomes 2 and 6, one on each chromosome respectively. Single QTL accounted for 6.7 to 19.3% of phenotypic variation. Identification method of salt tolerance in rice and breeding of rice varieties with salt tolerance based on molecular markers assisted selection had been discussed.

QTL underlying iron and zinc toxicity tolerances at seedling stage revealed by two sets of reciprocal introgression populations of rice(Oryza sativa L.)

Iron and zinc are two trace elements that are essential for rice. But they are toxic at higher concentrations, leading to severe rice yield losses especially in acid soils and inland valleys. In this study, two reciprocal introgression line(IL) populations sharing the same parents were used with high-density SNP bin markers to identify QTL tolerant to iron and zinc toxicities. The results indicated that the japonica variety 02,428 had stronger tolerance to iron and zinc toxicities than the indica variety Minghui 63. Nine and ten QTL contributing to iron and zinc toxicity tolerances,respectively, were identified in the two IL populations. The favorable alleles of most QTL came from 02,428. Among them, q FRRDW2, q ZRRDW3, and q FRSDW11 appeared to be independent of genetic background. The region C11S49–C11S60 on chromosome 11 harbored QTL affecting multiple iron and zinc toxicity tolerance-related traits, indicating partial genetic overlap between the two toxicity tolerances. Our results provide essential information and materials for developing excellent rice cultivars with iron and/or zinc tolerance by marker-assisted selection(MAS).

Evaluation of Rice Seedling Tolerance to Constant and Intermittent Low Temperature Stress

M202, IR50 and advanced backcross （BC4F6） lines carrying the cold tolerance QTLs qCTS4 and qCTS12 were evaluated using three low temperature stress assays （constant, intermittent and constant with recovery period）. Under constant stress, two BC4F6 lines （MIb 4853-9 and MIb 6885-2） exhibited differences in seedling growth and accumulation of stress-related compounds although both carry the two QTLs in the IRS0 background. Differences between these lines were also observed in the constant with recovery period assay, although both of them performed comparably under intermittent stress, MIb 6885-2 performed more similarly to M202 in the constant and constant with recovery period assays, suggesting that this line contains an introgressed region（s） not present in MIb 4853-9. The three assays were also applied to assess variations in cold tolerance in a set of diverse germplasms. Performance metrics and visual ratings were comparable for evaluating tolerance to constant stress. However, differences in response to intermittent stress were more evident from growth and total chlorophyll measurements than from visual ratings. With regard to the constant with recovery period assay, about 15% of the germplasm accessions did not recover. However, some lines which exhibited chilling injuries of comparable severity were able to overcome them. This recovery phenotype may improve rice performance in the field and warrant further investigation.

Mapping QTLs for Drought Tolerance at Seedling Stage in Rice Using Doubled Haploid Population

QTLs for drought tolerance at the rice seedling stage were analyzed using a doubled haploid （DH） population consisted of 251 lines from the cross between a japonica parent Maybelle and an indica parent Baiyeqiu. A genetic linkage map with 226 SSR marker loci was constructed. Single-locus analysis following composite interval mapping （CIM） detected a total of five QTLs located on five different chromosomes of rice. Four QTLs were also detected following two-locus analysis, resolving two pairs of epistatic QTLs （E-QTI_s） with positive and additive genetic effects. The results indicated that the alleles from the parent Baiyeqiu contributed DH population to improve drought tolerance at the seedling stage.

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.

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.

Identification of quantitative trait loci associated with salt tolerance at seedling stage from Oryza rufipogon

Soil salinity is one of the major abiotic stresses affecting plant growth and crop production.In the present study,salt tolerance at rice seedling stage was evaluated using 87 introgression lines（ILs）,which were derived from a cross between an elite indica cultivar Teqing and an accession of common wild rice（Oryza rufipogon Griff.）.Substantial variation was observed for four traits including salt tolerance score（STS）, relative root dry weight（RRW）,relative shoot dry weight（RSW） and relative total dry weight（RTW）.STS was significantly positively correlated with all other three traits.A total of 15 putative quantitative trait loci（QTLs） associated with these four traits were detected using single-point analysis,which were located on chromosomes 1,2,3,6,7,9 and 10 with 8%-26%explaining the phenotypic variance.The O. rufipogon-derived alleles at 13 QTLs（86.7%） could improve the salt tolerance in the Teqing background.Four QTL clusters affecting RRW, RSW and RTW were found on chromosomes 6,7,9 and 10,respectively.Among these four QTL clusters,a major cluster including three QTLs （qRRWIO,qRSWIO and qRTWIO） was found near the maker RM271 on the long arm of chromosome 10,and the O.rufipogon-derived alleles at these three loci increased RRW,RSW and RTW with additive effects of 22.7%,17.3%and 18.5%,respectively,while the phenotypic variance explained by these three individual QTLs for the three traits varied from 19%to 26%.In addition,several salt tolerant ILs were selected and could be used for identifying and utilizing favorable salt tolerant genes from common wild rice and used in the salt tolerant rice breeding program.

Mapping Quantitative Trait Loci Associated with Aluminum Toxin Tolerance in NJRIKY Recombinant Inbred Line Population of Soybean (Glycine max)

To investigate the genetic mechanism of AI-tolerance in soybean, a recombinant inbred line population （RIL） with 184 F2：7：11 lines derived from the cross of Kefen9 No.1×Nannong 1138-2 （AI-tolerant×AI-sensitive） were tested in pot experiment with sand culture medium in net room in Nanjing. Four traits, i.e. plant height, number of leaves, shoot dry weight and root dry weight at seedling stage, were evaluated and used to calculate the average membership index （FAi） as the indicator of AI-tolerance. The composite interval mapping （CIM） under WinQTL Cartographer v. 2.5 detected five QTLs （i.e. qFAi-1, qFAi- 2, qFAi-3, qFAi-4 and qFAi-5）, explaining 5.20%-9.07% of the total phenotypic variation individually. While with the multiple interval mapping （MIM） of the same software, five QTLs （qFAi-1, qFAi.5, qFAi.6, qFAi-7, and qFAi-8） explaining 5.7%-24.60% of the total phenotypic variation individually were mapped. Here qFAi-1 and qFAi-5 were detected by both CIM and MIM with the locations in a same flanking marker region, GMKF046-GMKF080 on B1 and satt278-sat_95 on L, respectively. While qFAi-2 under CIM and qFAi-6 under MIM both on Dlb2 were located in neighboring regions with their confidence intervals overlapped and might be the same locus. Segregation analysis under major gene plus polygene inheritance model showed that AI-tolerance was controlled by two major genes （h^2mg=33.05%） plus polygenes （h^2pg=52.73%）. Both QTL mapping and segregation analysis confirmed two QTLs responsible for AI-tolerance with relatively low heritability, and there might be a third QTL, confounded with the polygenes in segregation analysis.

深水稻全生育期耐盐性状的QTL定位

盐胁迫是许多沿海地区水稻生产的主要制约因素,尤其是沿海地区的咸淡水交汇区域。耐盐性是一种复杂的性状,可以通过QTL定位来帮助耐盐育种,以培育更高耐盐性的水稻品种。本研究供体亲本为沿海深水稻品种赤禾,受体亲本为美国水稻品种Lemont,杂交获得174份F9代的重组自交系,在芽期、苗期和生殖生长期分别利用浓度为15 g L^(-1)、5 g L^(-1)和5~6 g L^(-1)的NaCl进行胁迫,通过芽期相对发芽率、苗期耐盐性评级和生殖生长期的7个表型性状为基础数据,利用142个SSR分子标记绘制连锁遗传图并进行QTL分析。鉴定结果发现,赤禾在芽期表现敏盐,在苗期和生殖生长期表现耐盐;Lemont相反。3个生长时期分别有70.11%、50.57%和60.34%的品系表现为弱耐盐性,而且耐盐性为弱的负相关。本研究共鉴定出33个LOD值为2.52~10.32的QTL,解释0.06%~13.68%的表型遗传变异,解释最大遗传变异的QTL均由耐盐亲本贡献,其中芽期4个、苗期6个和生殖生长期23个位点,并在生殖生长期发现4个QTL重叠区域。这些QTL可以进一步研究,不仅为提高水稻育种的耐盐性提供了新的遗传资源,还有助于在水稻耐盐育种中,提高水稻品种的耐盐性。

水稻生长早期耐冷性QTL分析

以籼粳交“密阳23/吉冷1号”的F2:3 代200个家系为作图群体,构建分子连锁图谱,并进行了F3 代家系的生长早期耐冷性鉴定和QTL分析。结果表明,幼苗期耐冷性、分蘖期耐冷性和低温下幼苗生长能力等生长早期耐冷性在F3 代表现为近似正态的连续分布,是由多基因控制的数量性状。在第1、5、9 染色体上分别检测到与幼苗期耐冷性相关的QTL各1个,其中qCTS1 对表型变异的解释率最大,达15.5%;在第2、3、7、9、11 染色体上分别检测到与分蘖期耐冷性相关的QTL各1个,而每个QTL对表型变异的解释率均较低;在第1、2、11、12染色体上分别检测到与低温下幼苗生长能力相关的QTL各1个,其中qGAS2 和qGAS12 对表型变异的解释率分别为26.6%和42.9%,是主效基因。

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。

水稻耐热性的QTL定位及耐热性与光合速率的相关性

应用典型的籼粳交组合IR6 4×Azucena花药培养的DH群体及其已构建的分子连锁图谱 ,在田间及温室高温条件下对该DH群体的结实性状进行考查 ,采用QTLmapper 1.0软件检测控制结实率的加性和上位性效应的QTL。在第1、3、4、8和 11等 5条染色体上 ,共检测到 6个具有加性效应的QTL ,其中位于第 1、3染色体的 2个加性效应QTL来自父本Azucena的等位基因 ,它们是耐热的QTL ,能分别提高结实率 9.5 0和 6 .46个百分点 ,其贡献率分别为 19.15 %和 2 86 %;位于其余 3条染色体的 4个加性效应的QTL来自母本IR6 4的等位基因 ,它能提高结实率 4.33～ 10 .37个百分点 ,在第 1、2、3、4、5、7、8、11等 8条染色体之间还检测到 8对加性×加性上位性效应 ,其贡献率为 2 .2 7%～ 8.13%。同时还对水稻分蘖盛期和抽穗期进行了光合速率的测定 ,发现抽穗期剑叶光合速率与耐热性呈显著的正相关。

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QTL3个,胶稠度高温耐性QTL6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。

水稻抽穗开花期耐热性QTL的定位分析

【目的】通过对水稻抽穗开花期耐热性的遗传研究,为水稻耐热种质资源的利用及分子标记辅助选择育种提供理论和实践依据。【方法】以2个籼稻品种T219(对高温敏感)和T226(耐高温)为亲本构建的202个株系的重组自交系(RILs),利用人工气候室进行了2年的高温处理试验,对RILs在抽穗开花期的耐热性状进行了主效应QTL以及QTL上位性分析。【结果】利用181个在亲本间具有多态性的SSR标记,构建了覆盖水稻全基因组1559.6cM、标记间平均距离为8.3cM的遗传连锁图谱。2年共检测到7个抽穗开花期耐热性主效应QTL以及7对上位性QTL。2004和2005年分别检测到3个和4个QTL,共解释29%和37.3%的表型变异。其中,qHt2、qHt3、qHt8和qHt12的耐热等位基因来自T226,而qHt9a和qHt9b的耐热等位基因来源于T219。位于第1、2、4、11和12染色体上4对QTL间以及位于第2、3、4、7、8和9染色体上的3对QTL间分别存在互作效应。【结论】水稻抽穗开花期耐热性受多个具有加性效应的基因控制,基因的效应比较小,基因间还存在互作效应。位于第3染色体的RM570-RM148标记位点(qHt3)在2年中同时检测到,可用于水稻耐热性分子标记辅助选择育种。

碱胁迫下粳稻幼苗前期耐碱性的数量性状基因座检测

以粳粳交"高产106/长白9号"F2:3代200个家系为作图群体,在0.15%Na2CO3溶液的碱性胁迫下,进行了水稻耐碱性鉴定,并以SSR标记构建的分子连锁图谱为基础,对水稻幼苗前期的根数、根长和苗高及其相对碱害率进行了数量性状基因座(QTLs)的检测。结果表明,上述性状在F3家系群中均表现为具有1～2个峰的连续分布,认为由主效基因和微效基因共同控制的数量性状。共检测到与碱胁迫下幼苗前期根数、根长和苗高及其相对碱害率相关的QTL26个,分布于第1、5、6、7、8、9和11染色体上。其中,碱胁迫下与根数相关的QTL4个,qRN6-1和qRN11对表型变异的解释率较大,分别为29.91%和13.42%;与根数相对碱害率相关的QTL5个,qRRN11-2对表型变异的解释率较大,为23.86%;与根长相关的QTL6个,qRRL11-2对表型变异的解释率较大,为21.06%;与根长相对碱害率相关的QTL2个,但对表型变异的解释率均较低;与苗高相关的QTL5个,qSH1和qSH11-2对表型变异的解释率较大,分别为15.81%和16.53%;与苗高相对碱害率相关的QTL4个,qRSH5和qRSH6-2对表型变异的解释率分别为29.89%和34.63%。而这些解释率较大的QTL所处的标记区间距离,除qRN6-1相对较小(19.0cM)外,其余QTL的标记区间距离均大于26.3cM,需作进一步的精细定位。在所检测到的QTL中,13个QTL的增效等位基因均来自耐碱亲本长白9号,而其余QTL的增效等位基因来自敏碱亲本高产106;基因的主要作用方式为超显性或部分显性。

水稻耐冷性遗传及基因定位研究概况与展望

综述了水稻低温发芽力 ,幼苗期、孕穗期和开花期耐冷性等遗传研究概况和近年来在水稻耐冷性数量性状基因定位 (QTLs)研究方面所取得的进展 。