Molecular mapping of quantitative trait loci for drought tolerance in maize plants

Drought tolerance is one of the most important but complex traits of crops. We looked for quantitative trait loci (QTLs) that affect drought tolerance in maize. Two maize inbreds and their advanced lines were evaluated for drought-related traits. A genetic linkage map developed using RFLP markers was used to identify QTLs associated with drought-related traits. Twenty-two QTLs were detected, with a minimum of one and a maximum of nine for drought-related traits. A single-QTL was detected for sugar concentration accounting for about 52.2% of the phenotypic variation on chromosome 6. A single-QTL was also identified for each of the traits root density, root dry weight, total biomass, relative water content, and leaf abscisic acid content, on chromosomes 1 and 7, contributing to 24, 0.2, 0.4, 7, and 19% of the phenotypic variance, respectively. Three QTLs were identified for grain yield on chromosomes 1, 5, and 9, explaining 75% of the observed phenotypic variability, whereas four QTLs were detected for osmotic potential on chromosomes 1, 3, and 9, together accounting for 50% of the phenotypic variance. Nine QTLs were detected for leaf surface area on chromosomes 3 and 9, with various degrees of phenotypic variance, ranging from 25.8 to 42.2%. Four major clusters of QTLs were identified on chromosomes 1, 3, 7, and 9. A QTL for yield on chromosome 1 was found co-locating with the QTLs for root traits, total biomass, and osmotic potential in a region of about 15 cM. A cluster of QTLs for leaf surface area were coincident with a QTL for osmotic potential on chromosome 3. The QTLs for leaf area also clustered on chromosome 9, whereas QTLs for leaf abscisic acid content and relative water content coincided on chromosome 7, 10 cM apart. Co-location of QTLs for different traits indicates potential pleiotropism or tight linkage, which may be useful for indirect selection in maize improvement for drought tolerance.     

Quantitative Trait Loci for Mercury Accumulation in Maize (Zea mays L.) Identified Using a RIL Population

To investigate the genetic mechanism of mercury accumulation in maize (Zea mays L.), a population of 194 recombinant inbred lines derived from an elite hybrid Yuyu 22, was used to identify quantitative trait loci (QTLs) for mercury accumulation at two locations. The results showed that the average Hg concentration in the different tissues of maize followed the order: leaves > bracts > stems > axis > kernels. Twenty-three QTLs for mercury accumulation in five tissues were detected on chromosomes 1, 4, 7, 8, 9 and 10, which explained 6.44% to 26.60% of the phenotype variance. The QTLs included five QTLs for Hg concentration in kernels, three QTLs for Hg concentration in the axis, six QTLs for Hg concentration in stems, four QTLs for Hg concentration in bracts and five QTLs for Hg concentration in leaves. Interestingly, three QTLs, qKHC9a, qKHC9b, and qBHC9 were in linkage with two QTLs for drought tolerance. In addition, qLHC1 was in linkage with two QTLs for arsenic accumulation. The study demonstrated the concentration of Hg in Hg-contaminated paddy soil could be reduced, and maize production maintained simultaneously by selecting and breeding maize Hg pollution-safe cultivars (PSCs).     

QTLs for days to silking in a recombinant inbred line maize population subjected to high and low nitrogen regimes

Days to silking (DTS) is one of the most important traits in maize (Zea mays). To investigate its genetic basis, a recombinant inbred line population was subjected to high and low nitrogen (N) regimes to detect quantitative trait loci (QTLs) associated with DTS. Three QTLs were identified under the high N regime; these explained 25.4% of the phenotypic variance. Due to additive effects, the QTL on chromosome 6 increased DTS up to 0.66 days; while the other two QTLs mapped on chromosome 9 (one linked with Phi061 and the other linked with Nc134) decreased DTS 0.89 and 0.91 days, respectively. Under low N regime, two QTLs were mapped on chromosomes 6 and 9, which accounted for 25.9% of the phenotypic variance. Owing to additive effects, the QTL on chromosome 6 increased DTS 0.67 days, while the other QTL on chromosome 9 decreased it 1.48 days. The QTL on chromosome 6, flanked by microsatellite markers Bnlg1600 and Phi077, was detected under both N regimes. In conclusion, we identified four QTLs, one on chromosome 6 and three on chromosome 9. These results contribute to our understanding of the genetic basis of DTS and will be useful for developing marker-assisted selection in maize breeding programs.     

Mapping quantitative trait loci associated with arsenic accumulation in rice (Oryza sativa)

The quantitative trait loci (QTLs) associated with arsenic (As) accumulation in rice were mapped using a doubled haploid population established by anther culture of F1 plants from a cross between a Japonica cultivar CJ06 and an Indica cultivar TN1 (Oryza sativa). Four QTLs for arsenic (As) concentrations were detected in the map. At the seedling stage, one QTL was mapped on chromosome 2 for As concentrations in shoots with 24.4% phenotypic variance and one QTL for As concentrations in roots was detected on chromosome 3. At maturity, two QTLs for As concentrations in grains were found on chromosomes 6 and 8, with 26.3 and 35.2% phenotypic variance, respectively. No common loci were detected among these three traits. Interestingly, the QTL on chromosome 8 was found to be colocated for As concentrations in grain at maturity and shoot phosphorus (P) concentrations at seedling stage. These results provide an insight into the genetic basis of As uptake and accumulation in rice, and will be useful in identifying genes associated with As accumulation.     

玉米雌雄开花间隔天数、结穗率与产量的数量性状位点(QTL)分析

采用SSR标记连锁图谱和复合区间作图法在山西灌溉和干旱胁迫条件下,对玉米(Zea mays L.)自交系黄早四×掖107组合的F3群体雌雄开花间隔天数(ASI)、结穗率和籽粒产量进行了数量性状位点(QTL)定位及基因效应分析.结果表明,在两种水分处理下,ASI、结穗率与籽粒产量的相关性均达到显著水平(P＜0.05).在灌溉和干旱胁迫下,分别检测到3个和2个控制ASI的QTL,位于第1、2、3和第2、5染色体上.在灌溉条件下,在第3和第6染色体上各检测到1个控制结穗率的QTL,基因作用方式呈加性或部分显性,可解释19.9%的表型变异;在干旱条件下,在第3、 7、10染色体上共检测到4个控制结穗率的QTL,基因作用方式为显性或部分显性,可解释60.4%的表型变异.在灌溉和干旱胁迫下,控制产量的QTL分别定位在第3、6、7和第1、2、4、8染色体上,基因作用方式均以加性或部分显性为主,可解释的表型变异为7.3%～22.0%.在干旱条件下,借助连锁分子标记和基因效应分析,可构建包含ASI、结穗率和产量QTL的选择指数,用于分子标记辅助育种.     

Identification of quantitative trait loci associated with small brown planthopper (Laodelphax striatellus Fallén) resistance in rice (Oryza sativa L.)

F(2) and BC(1) populations derived from the cross between 02428 / Rathu Heenati were used to investigate small brown planthopper (SBPH) resistance. Using the F(2) population, three QTLs for antixenosis against SBPH were located on chromosomes 2, 5 and 6, and accounted for 30.75% of the phenotypic variance; three QTLs for antibiosis against SBPH were detected on chromosomes 8, 9 and 12. qSBPH5-c explaining 7.21% of phenotypic variance for antibiosis was identified on chromosome 5 using the BC(1) population. A major QTL, qSBPH12-a1, explained about 40% of the phenotypic variance, and a minor QTL, qSBPH4-a, was detected by the SSST method in both the F(2) and BC(1) populations. The QTLs indentified in the present study will be useful for marker assisted selection of SBPH resistance in rice.     

拔节期与抽穗期玉米抗纹枯病相关QTL的初步定位

以玉米自交系R15(抗)×478(感)的F_2分离群体为作图群体,构建了包含146个SSR标记位点的遗传连锁图谱,覆盖玉米基因组1666 cM,平均图距11．4 cM。通过麦粒嵌入法对229个F_(2：4)家系进行人工接种纹枯病菌,于玉米拔节期和抽穗期进行纹枯病的抗性鉴定。应用复合区间作图法分析两个时期的抗病QTL及遗传效应。结果共检测到17个抗性QTL,其中以拔节期病情指数为指标共检测到9个QTL,分别位于第1、2、3、4、5、6、和10染色体上,可解释的表型变异为3．72%-9．26%;以抽穗期的病情指数为指标共在7条染色体上检测到10个抗玉米纹枯病的QTL,分布于第2、3、4、5、6、8和9染色体上。单个QTL可解释的表型变异为4．27%-9．27%。两个时期共检测出2个共同QTL,它们分别位于第2染色体的bnlgl662-bnlg1940区间和第6染色体的umc1006-umc1723区间。定位结果表明两个时期检测出的抗性QTL的差异表达与玉米不同发育时期基因的时空表达有密切关系,从而反映在纹枯病的抗性位点差异性上．这为玉米抗病选育提供新的信息。     

Identification of quantitative trait loci under drought conditions in tropical maize. 1. Flowering parameters and the anthesis-silking interval

Drought is an important climatic phenomenon which, after soil infertility, ranks as the second most severe limitation to maize production in developing countries. When drought stress occurs just before or during the flowering period, a delay in silking is observed, resulting in an increase in the length of the anthesis-silking interval (ASI) and in a decrease in grain yield. Selection for reduced ASI in tropical open-pollinated varieties has been shown to be correlated with improved yields under drought stress. Since efficient selection for drought tolerance requires carefully managed experimental conditions, molecular markers were used to identify the genomic segments responsible for the expression of ASI, with the final aim of developing marker-assisted selection (MAS) strategies. An F₂population of 234 individuals was genotyped at 142 loci and F₃ families were evaluated in the field under several water regimes for male flowering (MFLW), male sterility (STER), female flowering (FFLW) and ASI. The genetic variance of ASI increased as a function of the stress intensity, and the broad-sense heritabilites of MFLW, FFLW and ASI were high under stress conditions, being 86%, 82% and 78%, respectively. Putative quantitative trait loci (QTLs) involved in the expression of MFLW and/or FFLW under drought were detected on chromosomes 1, 2, 4, 5, 8, 9 and 10, accounting for around 48% of the phenotypic variance for both traits. For ASI, six putative QTLs were identified under drought on chromosomes 1, 2, 5, 6, 8 and 10, and together accounted for approximately 47% of the phenotypic variance. Under water stress conditions, four QTLs were common for the expression of MFLW and FFLW, one for the expression of ASI and MFLW, and four for the expression of ASI and FFLW. The number of common QTLs for two traits was related to the level of linear correlation between these two traits. Segregation for ASI was found to be transgressive with the drought-susceptible parent contributing alleles for reduced ASI (4 days) at two QTL positions. Alleles contributed by the resistant line at the other four QTLs were responsible for a 7-day reduction of ASI. These four QTLs represented around 9% of the linkage map, and were stable over years and stress levels. It is argued that MAS based on ASI QTLs should be a powerful tool for improving drought tolerance of tropical maize inbred lines.     

QTLs for Na<Superscript>+</Superscript> and K<Superscript>+</Superscript> uptake of the shoots and roots controlling rice salt tolerance

An F₂ and an equivalent F₃ population derived from a cross between a high salt-tolerance indica variety, Nona Bokra, and a susceptible elite japonica variety, Koshihikari, were produced. We performed QTL mapping for physiological traits related to rice salt-tolerance. Three QTLs for survival days of seedlings (SDSs) under salt stress were detected on chromosomes 1, 6 and 7, respectively, and explained 13.9% to 18.0% of the total phenotypic variance. Based on the correlations between SDSs and other physiological traits, it was considered that damage of leaves was attributed to accumulation of Na⁺ in the shoot by transport of Na⁺ from the root to the shoot in external high concentration. We found eight QTLs including three for three traits of the shoots, and five for four traits of the roots at five chromosomal regions, controlled complex physiological traits related to rice salt-tolerance under salt stress. Of these QTLs, the two major QTLs with the very large effect, qSNC-7 for shoot Na⁺ concentration and qSKC-1 for shoot K⁺ concentration, explained 48.5% and 40.1% of the total phenotypic variance, respectively. The QTLs detected between the shoots and the roots almost did not share the same map locations, suggesting that the genes controlling the transport of Na⁺ and K⁺ between the shoots and the roots may be different.     

玉米籽粒重金属铅(Pb2+)含量的QTL定位

铅(Pb²⁺)是现存环境最大量的有毒重金属污染元素,在我国特别是西南地区种植的玉米受重金属Pb²⁺污染日益严重,已严重影响到食物安全。文章利用玉米籽粒Pb²⁺低富集自交系178和籽粒Pb²⁺高富集自交系9782杂交衍生的重组自交系群体为作图群体,利用165对SSR多态性标记,构建了总长度为1499.85 cM、标记间平均距离为9.07 cM的分子遗传图谱,对玉米籽粒Pb²⁺含量性状进行了QTL定位分析,以期为选育籽粒低富集Pb²⁺的玉米新品种提供参考。结果表明,在Pb²⁺浓度为333.32 mg/kg胁迫下,共检测到2个与籽粒Pb²⁺含量相关的QTL,分别位于玉米第1、第4号染色体,其中qPC1位于标记区间umc1661~phi002h之间,表型贡献率为11.13%,加性效应为0.062;qPC4位于umc1117~nc005之间,表型贡献率为5.55%,加性效应为-0.044。性状相关分析结果表明,籽粒中Pb²⁺含量与穗长、穗粗、行粒数、穗重和百粒重等产量性状间均未达到显著水平,表明选育玉米籽粒Pb²⁺低富集的新自交系或杂交种不一定会影响到产量性状,而且籽粒Pb²⁺含量是一个相对独立的遗传性状。     

Quantitative trait loci mapping of resistance to Laodelphax striatellus (Homoptera: Delphacidae) in rice using recombinant inbred lines

Laodelphax striatellus Fallén (Homoptera: Delphacidae), is a serious pest in rice, Oryza sativa L., production. A mapping population consisting of 81 recombinant inbred lines (RILs), derived from a cross between japonica' Kinmaze' and indica' DV85' rice, was used to detect quantitative trait loci (QTLs) for the resistance to L. striatellus. Seedbox screening test (SST), antixenosis test, and antibiosis test were used to evaluate the resistance response of the two parents and 81 RILs to L. striatellus at the seedling stage, and composite interval mapping was used for QTL analysis. When the resistance was measured by SST method, two QTLs conferring resistance to L. striatellus were mapped on chromosome 11, namely, Qsbph11a and Qsbph11b, with log of odds scores 2.51 and 4.38, respectively. The two QTLs explained 16.62 and 27.78% of the phenotypic variance in this population, respectively. In total, three QTLs controlling antixenosis against L. striatellus were detected on chromosomes 3, 4, and 11, respectively, accounting for 37.5% of the total phenotypic variance. Two QTLs expressing antibiosis to L. striatellus were mapped on chromosomes 3 and 11, respectively, explaining 25.9% of the total phenotypic variance. The identified QTL located between markers XNpb202 and C1172 on chromosome 11 was detected repeatedly by three different screening methods; therefore, it may be important to confer the resistance to L. striatellus. Once confirmed in other mapping populations, these QTLs should be useful in breeding for resistance to L. striatellus by marker-assisted selection of different resistance genes in rice varieties.     

Mapping of QTL for downy mildew resistance in maize

Quantitative trait loci (QTLs) of maize involved in mediating resistance to Peronosclerospora sorghi, the causative agent of sorghum downy mildew (SDM), were detected in a population of recombinant inbred lines (RILs) derived from the Zea mays L. cross between resistant (G62) and susceptible (G58) inbred lines. Field tests of 94 RILs were conducted over two growing seasons using artificial inoculation. Heritability of the disease reaction was high (around 70%). The mapping population of the RILs was also scored for restriction fragment length polymorphic (RFLP) markers. One hundred and six polymorphic RFLP markers were assigned to ten chromosomes covering 1648 cM. Three QTLs were detected that significantly affected resistance to SDM combined across seasons. Two of these mapped quite close together on chromosome 1, while the third one was on chromosome 9. The percentage of phenotypic variance explained by each QTL ranged from 12.4% to 23.8%. Collectively, the three QTLs identified in this study explained 53.6% of the phenotypic variation in susceptibility to the infection. The three resistant QTLs appeared to have additive effects. Increased susceptibility was contributed by the alleles of the susceptible parent. The detection of more than one QTL supports the hypothesis that several qualitative and quantitative genes control resistance to P. sorghi.     

玉米叶绿素含量的QTL定位

为了探讨玉米叶绿素含量的遗传规律, 以A150-3-2×Mo17杂交组配的189个F2单株作为作图群体, 构建了具有112个标记位点的玉米分子遗传图谱, 于喇叭口期和开花期分别进行了玉米叶绿素a含量(chla), 叶绿素b含量(chlb), 其他叶绿素含量(chlc)和叶绿素总含量(chlz)4个性状的测定, 并进行QTL分析。在喇叭口期和开花期共检测到32个QTL, 分布在除第6和10染色体以外的其他染色体上。在喇叭口期检测到24个QTL, 分布于第1、2、3、5、7、8和9染色体上, 叶绿素a、叶绿素b、其他叶绿素和叶绿素总含量各检测到6个QTL, 在同一区间内检测到的4个性状的QTL之间的距离在0~2 cM之间。喇叭口期检测到控制叶绿素a、叶绿素b、其他叶绿素和叶绿素总含量的4个主效QTL位于第5染色体上的umc1098~bnlg557区间, 分别可解释表型变异的11.63%、10.3%、10.77%和11.51%。开花期检测到8个QTL, 分布于第4和5染色体上。其中叶绿素a、叶绿素b、其他叶绿素和叶绿素总含量各2个QTL。标记umc1098和bnlg557之间同时存在控制喇叭口期4个叶绿素含量性状的QTL和开花期控制叶绿素a和叶绿素b的QTL。标记umc2308和bnlg386之间只存在控制开花期4个叶绿素含量性状的QTL。     

Identification of QTLs for Yield and Associated Traits in F₂ Population of Rice

Identification of quantitative trait loci (QTLs) controlling yield and yield-related traits in rice was performed in the F₂ mapping population derived from parental rice genotypes DHMAS and K343. A total of 30 QTLs governing nine different traits were identified using the composite interval mapping (CIM) method. Four QTLs were mapped for number of tillers per plant on chromosomes 1 (2 QTLs), 2 and 3; three QTLs for panicle number per plant on chromosomes 1 (2 QTLs) and 3; four QTLs for plant height on chromosomes 2, 4, 5 and 6; one QTL for spikelet density on chromosome 5; four QTLs for spikelet fertility percentage (SFP) on chromosomes 2, 3 and 5 (2 QTLs); two QTLs for grain length on chromosomes 1 and 8; three QTLs for grain width on chromosomes1, 3 and 8; three QTLs for 1000-grain weight (TGW) on chromosomes 1, 4 and 8 and six QTLs for yield per plant (YPP) on chromosomes 2 (3 QTLs), 4, 6 and 8. Most of the QTLs were detected on chromosome 2, so further studies on chromosome 2 could help unlock some new chapters of QTL for this cross of rice variety. Identified QTLs elucidating high phenotypic variance can be used for marker-assisted selection (MAS) breeding. Further, the exploitation of information regarding molecular markers tightly linked to QTLs governing these traits will facilitate future crop improvement strategies in rice.     

Genetic loci mapping associated with maize kernel number per ear based on a recombinant inbred line population grown under different nitrogen regimes

Kernel number per ear (KNE) is one of the most important yield-related agronomic traits in maize (Zea mays). To clarify its genetic basis, we made a quantitative trait locus (QTL) analysis of KNE in a recombinant inbred line population derived from lines Mo17 and Huangzao4, under two nitrogen (N) regimes. Seven QTLs, on chromosomes 4, 6 and 9, were mapped under the high N regime, which explained phenotypic variation ranging from 5.03 to 15.49%. Under the low N regime, three QTLs were located on chromosomes 6 and 9, which accounted for phenotypic variation ranging from 8.54 to 12.21%. These QTLs had different mapping intervals to their nearest markers, ranging from 0 to 16.5 cM. According to the chromosome positions and genetic effects of these QTLs, only seven QTLs for KNE were identified in our experiment, out of which three were found under both N regimes, on chromosomes 6 (one) and 9 (two); the other four were mapped only under the high N regime, on chromosomes 4 (three) and 6 (one). This information could be useful for developing marker-assisted selection in maize-breeding projects.     

不同发育时期小麦粒重性状QTL的动态分析

利用6044×01-35构建的重组自交系(RIL)群体为试验材料,对小麦粒重性状进行发育动态QTL分析。结果表明,在小麦花后子粒灌浆的7个不同时期,两个试验点共检测到16个与粒重性状相关的QTL。其中开花后20d检测到的单穗粒重QTL位于2A染色体上,解释率达12%,遗传效应超过10;两环境下控制千粒重QTL在7个时期均被检测到。花后的各个时期均能在Xgwm448-Xgpw7399标记区间定位到千粒重QTL。其中花后10d检测到1个千粒重QTL,位于2A染色体的Xgwm448-Xgpw7399标记区间,解释较大的表型变异,达到18%。Qtl8、Qtl13和Qtl14均定位在Xgwm448-Xgpw7399标记区间的同一位置,共同解释11%的表型变异。花后20d和花后25d均检测到1个QTL,位于2A染色体的Xgwm372-Xgwm95标记区间的不同位点,均能解释4%的表型变异。花后40d检测到1个QTL,位于1D染色体的Xwmc93-Xgpw2224标记区间,解释1%的表型变异。从连锁群的位置上看,控制千粒重的QTL主要集中在2A染色体的Xgwm448-Xgpw7399标记区间,这是一个控制千粒重QTL的富集区域,以期进行精细定位和图位克隆。     

A region of maize chromosome 2 affects response to downy mildew pathogens

Quantitative trait loci (QTLs) for downy mildew resistance in maize were identified based on co-segregation with linked restriction fragment length polymorphisms or simple sequence repeats in 220 F2 progeny from a cross between susceptible and resistant parents. Disease response was assessed on F3 families in nurseries in Egypt, Thailand, and South Texas and after inoculation in a controlled greenhouse test. Heritability of the disease reaction was high (around 93% in Thailand). One hundred and thirty polymorphic markers were assigned to the ten chromosomes of maize with LOD scores exceeding 4.9 and covering about 1,265 cM with an average interval length between markers of 9.5 cM. About 90% of the genome is located within 10 cM of the nearest marker. Three putative QTLs were detected in association with resistance to downy mildew in different environments using composite interval mapping. Despite environmental and symptom differences, one locus on chromosome 2 had a major effect and explained up to 70% of the phenotypic variation in Thailand where disease pressure was the highest. The other two QTLs on chromosome 3 and chromosome 9 had minor effects; each explained no more than 4% of the phenotypic variation. The three QTLs appeared to have additive effects on resistance, identifying one major gene and two minor genes that contribute to downy mildew resistance.     

Identification of quantitative trait loci controlling linolenic acid concentration in PI483463 (Glycine soja)

Key message

The QTLs controlling alpha-linolenic acid concentration from wild soybean were mapped on nine soybean chromosomes with various phenotypic variations. New QTLs for alpha-linolenic acid were detected in wild soybean.

Abstract

Alpha-linolenic acid (ALA) is a polyunsaturated fatty acid desired in human and animal diets. Some wild soybean (Glycine soja) genotypes are high in ALA. The objective of this study was to identify quantitative trait loci (QTLs) controlling ALA concentration in a wild soybean accession, PI483463. In total, 188 recombinant inbred lines of F_5:6, F_5:7, and F_5:8 generations derived from a cross of wild soybean PI483463 (~15 % ALA) and cultivar Hutcheson (~9 % ALA) were planted in four environments. Harvested seeds were used to measure fatty acid concentration. Single nucleotide polymorphism markers of the universal soybean linkage panel (USLP 1.0) and simple sequence repeat markers were used for molecular genotyping. Nine putative QTLs were identified that controlled ALA concentration by model-based composite interval mapping and mapped to different soybean chromosomes. The QTLs detected in four environments explained 2.4–7.9 % of the total phenotypic variation (PV). Five QTLs, qALA5_3, qALA6_1, qALA14_1, qALA15_1, and qALA17_1, located on chromosomes 5, 6, 14, 15, and 17 were identified by model-based composite interval mapping and composite interval mapping in two individual environments. Among them, qALA6_1 showed the highest contribution to the PV with 10.0–10.2 % in two environments. The total detected QTLs for additive and epistatic effects explained 52.4 % of the PV for ALA concentration. These findings will provide useful information for understanding genetic structure and marker-assisted breeding programs to increase ALA concentration in seeds derived from wild soybean PI483463.     

Mapping QTLs influencing rice floral morphology using recombinant inbred lines derived from a cross between <Emphasis Type="Italic">Oryza sativa</Emphasis> L. and <Emphasis Type="Italic">Oryza rufipogon</Emphasis> Griff

To understand the genetic basis of floral traits associated with the mating system in rice, we analyzed pistil, stamen and glume traits using a recombinant inbred line population, derived from a cross between an Asian cultivated rice ( Oryza sativa L.), Pei-kuh, and a wild rice ( Oryza rufipogon Griff.), W1944. Quantitative trait loci (QTLs) affecting floral morphology were detected by composite interval mapping using a linkage map constructed using 147 markers, mostly RFLPs. A total of 7, 4, 14 and 6 QTLs were detected for traits related to pistil, stamen, and size and shape of the glume, respectively. Comparison of 31 QTLs affecting these organs revealed ten QTLs affecting the different organs in four adjacent regions on chromosomes 2, 4, 5 and 10, but most QTLs (68%) were located separately on the whole chromosomes. Although four QTLs for stigma breadth, anther length and thickness of lemma and palea explained more than 25% of the total phenotypic variance, most QTLs (87%) had smaller effects. These results suggest that quantitative variation observed for pistil, stamen and glume traits is controlled by several distinct genes with small effects.     

QTL mapping of yield, agronomic and quality traits in tetraploid potato (Solanum tuberosum subsp. tuberosum)

Interval mapping of quantitative trait loci (QTL) for 16 yield, agronomic and quality traits in potato was performed on a tetraploid full-sib family comprising 227 clones from a cross between processing clone 12601ab1 and table cultivar Stirling. Thirty-eight AFLP primer combinations and six SSRs provided 514 informative markers which formed a molecular marker map comprising 12 linkage groups (LGs) in 12601ab1 (nine with four homologous chromosomes) which were aligned with 12 in Stirling (11 with four homologous chromosomes), with four partial groups remaining in 12601ab1. Two LGs were identified unequivocally as chromosomes IV and V and eight others were tentatively assigned with chromosomes VII and X unidentified. All of the traits scored had moderately high heritabilities with 54–92% of the variation in clone means over 3 years and two replicates being due to genetic differences. A total of 39 QTLs were identified. A QTL for maturity was identified on chromosome V which explained 56% of the phenotypic variance, whereas the other QTLs individually explained between 5.4 and 16.5%. However, six QTLs were detected for after-cooking blackening and four for each of regularity of tuber shape, fry colour both after storage at 4 and 10°C and sprouting. Just two QTLs were found for each of yield, the two ‘overall’ scores, crop emergence, tuber size and common scab and just one QTL was detected for each of dry matter content, keeping quality, growth cracks and internal condition. The implications for practical potato breeding and for practical linkage and QTL analysis in autotetraploids are discussed.