QTLs for drought escape and tolerance identified in a set of random introgression lines of rice

A large set of 254 introgression lines in an elite indica genetic background were evaluated for grain yield (GY) and related traits under the irrigated (control) and drought (stress) conditions in two consecutive years for genetic dissection of adaptive strategies of rice to water stress. A total of 36 quantitative trait loci (QTLs) affecting heading date (HD), plant height (PH), GY and yield components were identified and most QTLs showed pronounced differential expression either qualitatively or quantitatively in response to drought. These QTLs could be grouped into three major types based on their behaviors under control and stress conditions. Type I included 12 QTLs that expressed under both the stress and non-stress conditions. Type II comprised 17 QTLs that expressed under irrigation but not under stress. Type III included seven QTLs that were apparently induced by stress. The observation that the Lemont (japonica) alleles at all HD QTLs except QHd5 resulted in early heading under stress appeared to be responsible for the putative adaptation of Lemont to drought by escaping, whereas the Teqing (indica) alleles at most PH/GY QTLs were consistently associated with increased yield potential and trait stability and thus contributed to DT. Our result that most DT QTLs were non-allelic with QTLs for drought escaping suggests that the two adaptive strategies in the parental lines are under possible negative regulation of two largely non-overlapping genetic systems.     

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 (qRRW10,qRSW10 and qRTW10) 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 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.     

Recent Advances in Genetics of Salt Tolerance in Tomato

Salinity is an important environmental constraint to crop productivity in arid and semi-arid regions of the world. Most crop plants, including tomato, Lycopersicon esculentum Mill., are sensitive to salinity throughout the ontogeny of the plant. Despite considerable research on salinity in plants, there are only a few instances where salt-tolerant cultivars have been developed. This is due in part to the complexity of the trait. A plant's response to salt stress is modulated by many physiological and agronomical characteristics, which may be controlled by the actions of several to many genes whose expressions are influenced by various environmental factors. In addition, salinity tolerance is a developmentally regulated, stage-specific phenomenon; tolerance at one stage of plant development is often not correlated with tolerance at other stages. Specific ontogenic stages should be evaluated separately for the assessment of tolerance and the identification, characterization, and utilization of useful genetic components. In tomato, genetic resources for salt tolerance have been identified largely within the related wild species, and considerable efforts have been made to characterize the genetic controls of tolerance at various developmental stages. For example, the inheritance of several tolerance-related traits has been determined and quantitative trait loci (QTLs) associated with tolerance at individual developmental stages have been identified and characterized. It has been determined that at each stage salt tolerance is largely controlled by a few QTLs with major effects and several QTLs with smaller effects. Different QTLs have been identified at different developmental stages, suggesting the absence of genetic relationships among stages in tolerance to salinity. Furthermore, it has been determined that in addition to QTLs which are population specific, several QTLs for salt tolerance are conserved across populations and species. Research is currently underway to develop tomatoes with improved salt tolerance throughout the ontogeny of the plant by pyramiding QTLs through marker-assisted selection (MAS). Transgenic approaches also have been employed to gain a better understanding of the genetics of salt tolerance and to develop tomatoes with improved tolerance. For example, transgenic tomatoes with overexpression of a single-gene-controlled vacuolar Na⁺/H⁺ antiport protein, transferred from Arabidopsis thaliana, have exhibited a high level of salt tolerance under greenhouse conditions. Although transgenic plants are yet to be examined for field salt tolerance and salt-tolerant tomatoes are yet to be developed by MAS, the recent genetic advances suggest a good prospect for developing commercial cultivars of tomato with enhanced salt tolerance in near future.     

QTL studies reveal little relevance of chilling-related seedling traits for yield in maize

Prolonged low temperature phases and short-term cold spells often occur in spring during the crucial stages of early maize (Zea mays L.) development. The effect of low temperature-induced growth retardation at the seedling stage on final yield is poorly studied. Therefore, the aim was to identify genomic regions associated with morpho-physiological traits at flowering and harvest stage and their relationship to previously identified quantitative trait loci (QTLs) for photosynthesis and morpho-physiological traits from the same plants at seedling stage. Flowering time, plant height and shoot biomass components at harvest were measured in a dent mapping population for cold tolerance studies, which was sown in the Swiss Midlands in early and late spring in two consecutive years. Early-sown plants exhibited chilling stress during seedling stage, whereas late-sown plants grew under favorable conditions. Significant QTLs, which were stable across environments, were found for plant height and for the time of flowering. The QTLs for flowering were frequently co-localized with QTLs for plant height or ear dry weight. The comparison with QTLs detected at seedling stage revealed only few common QTLs. A pleiotropic effect was found on chromosome 3 which revealed that a good photosynthetic performance of the seedling under warm conditions had a beneficial effect on plant height and partially on biomass at harvest. However, a high chilling tolerance of the seedling seemingly had an insignificant or small negative effect on the yield.     

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.     

Genetic dissection of chlorophyll content at different growth stages in common wheat

Quantitative trait loci (QTLs) for chlorophyll content were studied using a doubled haploid (DH) population with 168 progeny lines, derived from a cross between two elite Chinese wheat cultivars Huapei 3 × Yumai 57. Chlorophyll content was evaluated at the maximum tillering stage (MS), the heading stage (HS), and the grain filling stage (GS), at three different environments in 2005 and 2006 cropping seasons. QTL analyses were performed using a mixed linear model approach. A total of 17 additive QTLs and nine pairs of epistatic QTLs were detected. Ten of 17 additive QTLs for chlorophyll content were persistently expressed at more than two growth stages, which suggest developmentally regulated loci controlling genetics for chlorophyll content in different growth stages in wheat. One novel major QTL for chlorophyll content was closely linked with the PCR marker Xwmc215 and was persistently expressed at three growth stages.     

Mapping of QTLs associated with cold tolerance during the vegetative stage in rice

Low-temperature stress is an important factor affecting the growth and development of rice (Oryza sativa L.) in temperate and high-elevation areas. Cold stress may cause various seedling injuries, delayed heading and yield reduction due to spikelet sterility. In this study, 181 microsatellite marker loci were used to identify quantitative trait loci (QTLs) associated with cold tolerance at the vegetative stage in 191 recombinant inbred lines (RILs) derived from a cross of a cold-tolerant temperate japonica cultivar (M-202) with a cold-sensitive indica cultivar (IR50). Different temperature regimes were applied in growth chambers on 191 RILs. The temperature regimes imposed in the growth chamber simulated cold-stress injuries at the seedling and late vegetative stages. In this study a major QTL was identified on chromosome 12, designated as qCTS12a, that was closely associated with cold-induced necrosis and wilting tolerance, and accounted for 41% of the phenotypic variation. A number of QTLs with smaller effects were also detected on eight rice chromosomes.     

Complex genetics controls natural variation among seed quality phenotypes in a recombinant inbred population of an interspecific cross between Solanum lycopersicum × Solanum pimpinellifolium

Seed quality in tomato is associated with many complex physiological and genetic traits. While plant processes are frequently controlled by the action of small‐ to large‐effect genes that follow classic Mendelian inheritance, our study suggests that seed quality is primarily quantitative and genetically complex. Using a recombinant inbred line population of Solanum lycopersicum × Solanum pimpinellifolium, we identified quantitative trait loci (QTLs) influencing seed quality phenotypes under non‐stress, as well as salt, osmotic, cold, high‐temperature and oxidative stress conditions. In total, 42 seed quality traits were analysed and 120 QTLs were identified for germination traits under different conditions. Significant phenotypic correlations were observed between germination traits under optimal conditions, as well as under different stress conditions. In conclusion, one or more QTLs were identified for each trait with some of these QTLs co‐locating. Co‐location of QTLs for different traits can be an indication that a locus has pleiotropic effects on multiple traits due to a common mechanistic basis. However, several QTLs also dissected seed quality in its separate components, suggesting different physiological mechanisms and signalling pathways for different seed quality attributes.     

Mapping QTLs conferring salt tolerance during germination in tomato by selective genotyping

This study was conducted to identify genomic regions (quantitative trait loci, QTLs) affecting salt tolerance during germination in tomato. Germination response of an F2 population of a cross between UCT5 (Lycopersicon esculentum, salt-sensitive) and LA716 (L. pennellii, salt-tolerant) was evaluated at a salt-stress level of 175 mM NaCl + 17.5 mM CaCl2 (water potential ca. –950 kPa). Germination was scored visually as radicle protrusion at 6 h intervals for 30 consecutive days. Individuals at both extremes of the response distribution (i.e., salt-tolerant and salt-sensitive individuals) were selected. The selected individuals were genotyped at 84 genetic markers including 16 isozymes and 68 restriction fragment length polymorphisms (RFLPs). Trait-based marker analysis (TBA) which measures changes (differences) in marker allele frequencies in selected lines was used to identify marker-linked QTLs. Eight genomic regions were identified on seven tomato chromosomes bearing genes (QTLs) with significant effects on this trait. The results confirmed our previous suggestion that salt tolerance during germination in tomato is polygenically controlled. The salt-tolerant parent contributed favorable QTL alleles on chromosomes 1, 3, 9 and 12 whereas the salt sensitive parent contributed favorable QTL alleles on chromosomes 2, 7 and 8. The identification of favorable alleles in both parents suggests the likelihood of recovering transgressive segregants in progeny derived from these parental genotypes. The results can be used for marker-assisted selection and breeding of salt-tolerant tomatoes.     

Genetic Dissection of Component Traits for Salinity Tolerance at Reproductive Stage in Rice

Plant Molecular Biology Reporter - Rice is highly sensitive to salt stress at flowering stage. With the objective of detection of quantitative trait loci (QTLs) in multi-environment for this stage,...     

Quantitative trait loci (QTLs) for pollen thermotolerance detected in maize

Pollen thermotolerance is an important component of the adaptability of crops to high temperature stress. The tolerance level of the different genotypes in a population of 45 maize recombinant inbred lines was determined as the degree of injury caused by high temperature to pollen germinability (IPGG) and pollen tube growth (IPTG) in an in vitro assay. Both traits revealed quantitative variability and high heritability. The traits were genetically dissected by the analysis of molecular markers using 184 mapped restriction fragment length polymorphisms (RFLPs). Significant genetic correlation between the markers and the trait allowed us to identify a minimum number of five quatitative trait loci (QTLs) for IPGG and six QTLs for IPTG. Their chromosomal localization indicated that the two characters are controlled by different sets of genes. In addition, IPGG and IPTG were shown to be basically independent of the pollen germination ability and pollen tube growth rate under non-stress conditions. These results are discussed in relation to their possible utilization in a breeding strategy for the improvement of thermotolerance in maize.     

干旱胁迫下水稻柱头外露率加性、上位性效应和Q×E互作

在耐旱性筛选设施内对一套水稻重组自交系群体(共185个株系)进行两年的水分胁迫和非胁迫处理,调查每穗颖花数(sNP)、单边柱头外露率(PSES)、双边柱头外露率(PDES)和柱头总外露率(PES)等4个开花相关性状.方差分析结果显示年份、株系和水分处理,以及相互间互作的效应均达显著水平.表型相关以PSES和PES间最高(r=0.9752***),其次为PDES和PES (r=0.7150***),最次为PSES和PDES间(r=0.5424***).利用203个SSR标记建立的连锁图,胁迫和非胁迫条件下各检测到6个SNP的主效QTL,3～4个PSES、PDES和PES的主效QTL;检测到1～9对上位性QTL影响颖花数和柱头外露率.大部分加性和上位性效应的贡献率较低(0.76%～9.92%),仅有少数QTL或上位性QTL解释总方差的10%以上.一些主效和上位性QTL在PSES、PDES和PES间被共同检测到,解释了不同柱头外露率指标间高度正相关关系.几乎没有在水分胁迫和非胁迫两种条件下都检测到的QTL,暗示着干旱对颖花数和柱头外露率有严重的影响.     

Identification of quantitative trait loci for cadmium tolerance and accumulation in wheat

Quantitative trait loci (QTL) for Cadmium (Cd) tolerance and accumulation in wheat (Triticum aestivum L.) were identified, using 103 recombinant inbred lines (RILs) derived from a cross of Ch × Sh at germination and seedling stages. The traits of germination, growth and physiology were measured. Cd tolerance indexes (TI) were calculated for plants under Cd stress relative to control conditions. Cd concentrations in both root and shoot were determined and the amount of Cd accumulation and translocation calculated. The phenotypic variation of the above traits showed a continuous distribution pattern among the RILs. Twenty-six QTLs were detected, (16 of which were designated for the traits under the control and Cd stress, 8 for Cd tolerance and 2 for root Cd accumulation). These 26 QTLs individually could explain 7.97–60.16% of the phenotypic variation. Fourteen QTLs were positive (with the additive effects coming from Ch) while the remaining 12 QTLs were negative (with the additive effects contributed by Sh). No QTL were detected in the same region on the chromosomes of wheat. The results indicated that genetic mechanisms controlling the traits of Cd tolerance were independent from each other. Therefore, in this study, the properties of Cd tolerance and accumulation showed to be independent traits in wheat.     

Phenotype/genotype associations for yield and salt tolerance in a barley mapping population segregating for two dwarfing genes

Barley traits related to salt tolerance are mapped in a population segregating for a dwarfing gene associated with salt tolerance. Twelve quantitative trait loci (QTLs) were detected for seven seedling traits in doubled haploids from the spring barley cross Derkado x B83-12/21/5 when given saline treatment in hydroponics. The location of QTLs for seedling growth stage (leaf appearance rate), stem weight prior to elongation, and tiller number are reported for the first time. In addition, four QTLs were found for the mature plant traits grain nitrogen and plot yield. In total, seven QTLs are co-located with the dwarfing genes sdw1, on chromosome 3H, and ari-e.GP, on chromosome 5H, including seedling leaf response (SGa) to gibberellic acid (GA(3)). QTLs controlling the growth of leaves (GS2) on chromosomes 2H and 3H and emergence of tillers (TN2) and grain yield were independent of the dwarfing genes. Field trials were grown in eastern Scotland and England to estimate yield and grain composition. A genetic map was used to compare the positions of QTLs for seedling traits with the location of QTLs for the mature plant traits. The results are discussed in relation to the study of barley physiology and the location of genes for dwarf habit and responses to GA.     

Identification and validation of QTLs for salt tolerance during vegetative growth in tomato by selective genotyping.

The purpose of this study was to identify quantitative trait loci (QTLs) for salt tolerance (ST) during vegetative growth (VG) in tomato by distributional extreme analysis and compare them with the QTLs previously identified for this trait. A BC1 population (N = 792) of a cross between a moderately salt-sensitive Lycopersicon esculentum Mill. breeding line (NC84173, maternal and recurrent parent) and a salt-tolerant L. pimpinellifolium (Jusl.) Mill. accession (LA722) was evaluated for ST in solution cultures containing 700 mM NaCl + 70 mM CaCl2 (electrical conductivity, EC = 64 dS/m and phiw approximately -35.2 bars). Thirty-seven BC1 plants (4.7% of the total) that exhibited the highest ST were selected (referred to as the selected population), grown to maturity in greenhouse pots and self-pollinated to produce BC1S1 progeny seeds. The 37 selected BC1S1 progeny families were evaluated for ST and their average performance was compared with that of the parental BC1 population before selection. A realized heritability of 0.50 was obtained for ST in this population. The 37 selected BC1 plants were subjected to restriction fragment length polymorphism (RFLP) analysis using 115 markers, and marker allele frequencies were determined. Allele frequencies for the same markers were also determined in an unselected BC1 population (N = 119) of the same cross. A trait-based marker analysis (TBA), which measures differences in marker allele frequencies between selected and unselected populations, was used to identify marker-linked QTLs. Five genomic regions were detected on chromosomes 1, 3, 5, 6, and 11 bearing significant QTLs for ST. Except for the QTL on chromosome 3, all QTLs had positive alleles contributed from the salt tolerant parent LA722. Of the five QTLs, three (those on chromosomes 1, 3, and 5) were previously identified for this trait in another study, and thus were validated here. Only one of the major QTLs that was identified in our previous study was not detected here. This high level of conformity between the results of the two studies indicates the genuine nature of the identified QTLs and their potential usefulness for ST breeding using marker-assisted selection (MAS). A few BC1S1 families were identified with most or all of the QTLs and with a ST comparable to that of LA722. These families should be useful for the development of salt tolerant tomato lines via MAS.     

Genetic analysis of loci associated with partial resistance to <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> in rapeseed (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Sclerotinia stem rot is the most devastating disease of rapeseed (Brassica napus L.) in China. Quantitative trait loci (QTLs) involved in resistance to Sclerotinia sclerotiorum were detected in a rapeseed population of 128-F(2:3) families derived from a cross between the male sterility restorer line H5200 and a partial resistant line Ning RS-1. A total of 107 molecular markers including 72 RFLPs, 30 AFLPs, 3 SSRs and 2 RAPDs were employed to construct a genetic linkage map with 23 linkage groups covering 1,625.7 cM with an average space of 15.2 cM. Resistance was assessed empirically at two developmental stages: with a detached leaf inoculation at the seedling stage and in vivo stem inoculation at the mature plant stage. The observed resistance was scored for each plant as leaf resistance at the seedling stage (LRS) and stem resistance at the mature plant stage (SRM). A total of 13 loci were identified by one-way ANOVA and six QTLs were detected with MapMaker-QTL. We found that three of the six QTLs were associated with leaf resistance at the seedling stage and collectively accounted for 40.7% of the total phenotypic variation, each accounting for 23.2%, 16.6% and 13.6% respectively. Three QTLs were found corresponding to the disease resistance at the mature plant stage, explaining 49.0% of the phenotypic variation. Epistasis was observed for the resistance and the additive by additive interactions were the predominant type of epistasis. It was concluded that both single-locus QTLs and epistatic interactions played important roles in Sclerotinia resistance in rapeseed.     

Dissection of Additive, Epistatic Effect and Q × E Interaction of Quantitative Trait Loci Influencing Stigma Exsertion Under Water Stress in Rice

Four flowering related traits, spikelet number per panicle (SNP), percentage of single exserted stigma (PSES), dual exserted stigma (PDES) and total exserted stigma (PES) of a RI population with 185 lines under water stress and non-stress conditions for 2 years, were investigated in a drought tolerance screening facility. ANOVA results showed high significance between years, lines, and water stress treatments, together with interactions among them in pairs. Highest phenotypic correlation was found between PSES and PES (r = 0.9752^***), followed by PDES and PES (r = 0.7150^***), and PSES and PDES (r = 0.5424^***). Based on a linkage map of 203 SSR markers, six main effect QTLs were detected for SNP and three or four main effect QTLs were associated with PSES, PDES and PES under stress or non-stress conditions. There were one to nine pairs of epistatic QTLs influencing SNP and stigma exsertion. The contribution rates of additive and epistatic effects seemed to be in a low magnitude for most cases (0.76%-9.92%) while a few QTLs or QTL pairs explained more than 10% of total variance. Some main effect QTL and epistasis were commonly detected among PSES, PDES and PES, explaining the high positive correlation between them. Few QTLs were detected under both water stress and non-stress condition, implying that drought had severe impact on the genetic behaviors of both spikelet number and stigma exsertion.     

两种供氮水平下水稻生长后期相关性状的QTL定位

以特青为母本与Lemont杂交,然后用特青为轮回亲本回交,建立特青背景下的染色体片段置换系（CSSL）群体。在正常和低氮条件下分别在生长后期对株高（PH）、单株穗数（PN）、叶绿素含量（CC）、地上部干物重（SDW）和单株籽粒产量（YD）等性状进行了QTL分析,共检测到31个QTL。其中在正常供氮水平下控制PH、PN、CC、SDW和YD的QTL数目均为3个;在低氮水平下检测到5、4、5和2个影响PH、PN、CC和SDW的QTL,在低氮水平下没有检测到控制YD的位点。大部分QTL集中在第2、3、7、11和12染色体上,影响不同性状或在两种供氮水平下影响同一性状的QTL在染色体上成串或成簇分布。其中RM30-RM439、RM18-RM478、RM309-RM270、RM235-RM17等区域同时检测到控制两个以上性状的QTL,表现出明显的一因多效现象。推测仅在低氮水平下检测到的QTL可能跟水稻对低氮胁迫耐性有一定的关联。     

Identification of salt-tolerant QTLs with strong genetic background effect using two sets of reciprocal introgression lines in rice

Effect of genetic background on detection of quantitative trait locus (QTL) governing salinity tolerance (ST) was studied using two sets of reciprocal introgression lines (ILs) derived from a cross between a moderately salinity tolerant japonica variety, Xiushui09 from China, and a drought tolerant but salinity susceptible indica breeding line, IR2061-520-6-9 from the Philippines. Salt toxicity symptoms (SST) on leaves, days to seedling survival (DSS), and sodium and potassium uptake by shoots were measured under salinity stress of 140?mmol/L of NaCl. A total of 47 QTLs, including 26 main-effect QTLs (M-QTLs) and 21 epistatic QTLs (E-QTLs), were identified from the two sets of reciprocal ILs. Among the 26?M-QTLs, only four (15.4%) were shared in the reciprocal backgrounds while no shared E-QTLs were detected, indicating that ST QTLs, especially E-QTLs, were very specific to the genetic background. Further, 78.6% of the M-QTLs for SST and DSS identified in the reciprocal ILs were also detected in the recombinant inbred lines (RILs) from the same cross, which clearly brings out the background effect on ST QTL detection and its utilization in ST breeding. The detection of ILs with various levels of pyramiding of nonallelic M-QTL alleles for ST from Xiushui09 into IR2061-520-6-9 allowed us to further improve the ST in rice.