Genetic dissection of seed vigour under artificial ageing conditions using two joined maize recombinant inbred line populations

Seed vigour plays an important role in agricultural production, and seeds with high sowing quality are necessary for improving agriculture production. In our study, two connected maize recombinant inbred line (RIL) populations derived from Yu82 × Shen137 and Yu537A × Shen137 crosses were evaluated for the mean germination time (MGT) and other related traits under three artificial ageing treatments. We used meta‐analysis to integrate genetic maps and identify quantitative trait loci (QTLs) across the two populations. In total, 74 QTLs and 20 meta‐QTLs (mQTLs) were identified. Four key mQTLs, mQTL2‐2, mQTL5‐4, mQTL6 and mQTL8, which contained initial QTLs with R² values >10% and included 5–9 initial QTLs, may be hot spots of important QTLs for the associated traits. Twenty‐two key candidate genes associated with four seed vigour‐related traits mapped to 14 mQTLs. In particular, the GRMZM2G163749, GRMZM2G122172/GRMZM2G554885/GRMZM2G122871 and GRMZM2G150367 genes mapped within the important mQTL5–4, mQTL6 and mQTL8 regions, respectively. Fine mapping for the genetic regions of these three mQTLs merits further study and could be utilized for marker‐assisted breeding.     

8种水旱环境下2个玉米群体穗部性状QTL间的上位性及环境互作效应分析

深入剖析干旱胁迫条件下玉米穗部性状的遗传机制可为玉米抗旱高产分子育种提供参考依据。以大穗型旱敏感自交系TS141为共同亲本,分别与小穗型强抗旱自交系廊黄和昌7-2杂交,构建了含有202个(LTPOP)和218个(CTPOP)家系的F2:3群体,在8种水旱环境下进行单穗重、穗轴重、穗粒重、百粒重、出籽率及穗长等6个穗部性状的表型鉴定,并采用复合区间作图法(CIM)和基于混合线性模型的复合区间作图法(MCIM)对其进行单环境和多环境联合数量性状位点(QTL)分析。结果表明,采用CIM法,单环境下在2套F2:3群体间检测到62个穗部性状QTL,其中干旱胁迫环境下检测到38个QTL,进一步在2套F2:3群体多个干旱胁迫环境下检测到10个稳定表达的QTL (sQTL),分别位于Bin 1.01–1.03、Bin 1.03–1.04、Bin 1.05、Bin 1.07、Bin 1.07–1.08、Bin 2.04、Bin 4.08、Bin 5.06–5.07、Bin6.05和Bin 9.04–9.06。采用MCIM法,联合分析定位到54个穗部性状联合QTL,其中24个表现显著的QTL与环境互作(QTL×E), 17对参与了显著的加性与加性/显性(AA/AD)上位性互作,其表型贡献率较低。这些研究结果可为系统地剖析玉米穗部性状的分子遗传机制提供理论依据;且这2套F2:3群体多个环境下检测到的sQTL可作为穗部性状改良的重要候选染色体区段,用于图位克隆或抗旱高产分子育种,但要注重环境及上位性互作效应的影响。     

QTL for maize grain yield identified by QTL mapping in six environments and consensus loci for grain weight detected by meta‐analysis

Grain yield is the most important and complicated trait in maize. In this study, a total of 498 recombinant inbred lines (RIL) derived from a biparental cross of two elite inbred lines, 178 and P53, were grown in six different environments. Quantitative trait locus (QTL) mapping was conducted for three grain yield component traits (100 grain weight, ear weight and kernel weight per plant). Subsequently, meta‐analysis was performed after a comprehensive review of the research on QTL mapping for grain weight (100, 300 and 1000) using BioMercator V4.2. In total, 62 QTLs were identified for 100 grain weight, ear weight and kernel weight per plant in six environments. Forty‐three meta‐QTLs (MQTLs) were detected by meta‐analysis. A total of 13 candidate genes homologous to eight functionally characterized rice genes were found, and four candidate genes were located in the two hot spot regions of MQTL1.5 and MQTL2.3. Our results suggest that the combination of literature collection, meta‐analysis and homologous blast searches can offer abundant information for further fine mapping, marker‐assisted selection (MAS) breeding and map‐based cloning for maize.     

Genetic mapping of quantitative trait locus for the leaf morphological traits in a recombinant inbred line population by ultra-high–density maps across multi-environments of maize (Zea mays)

Leaf is the main organ of photosynthetic reaction of plants. Studying the genetic mechanism that affects the leaf shape is very important for the improvement of maize production. In this study, a RIL population, derived from a cross between Ye478 and Qi319, was planted in four different environments, and six leaf morphological traits were measured, including the leaf angle of first leaf above ear, the leaf angle of first leaf below ear, leaf orientation value, leaf area of first leaf above ear, leaf area of ear and leaf area of first leaf below ear. By combining with a genetic map containing 4,602 bin markers, 39 QTLs associated with leaf morphological traits were identified. Among them, four QTLs explained more than 10% of the phenotypic variance, and the QTL qLOV8-2 which controlled LOV not only had a phenotypic contribution rate of 13.86% but also was detected in four environments, which could be considered as a stable major QTL. These results provide useful information for understanding the molecular mechanisms controlling maize leaf morphological traits.     

Epistatic and QTL × environment interaction effects on leaf area‐associated traits in maize

Leaves play important roles, including in photosynthesis and transpiration, during plant development. Therefore, studying the genetic mechanisms affecting leaf size may contribute to improving plant architecture through molecular design. However, the genetic mechanisms that underlie these traits remain poorly understood. In this study, quantitative trait loci (QTL) for traits related to leaf area were identified using a set of recombinant inbred lines evaluated in three environments by 1226 single nucleotide polymorphic markers. In total, 16 QTL were detected with four QTL showing effects of greater than 10%. Five of the QTL explained 46.02%, seven of the QTL explained 46.77%, and four of the QTL explained 30.03% of the phenotypic variance of leaf length, width and area, respectively. Additional epistatic effects were identified for all of the maize chromosomes, except for chromosomes 7, 8 and 9. All of the epistatic effects involved pairs of loci on different chromosomes. Thus, a complex network controlling these traits was found in maize. These results provide useful information for understanding the molecular mechanisms controlling maize leaf size.     

利用回交导入系定位干旱环境下水稻植株水分状况相关QTL

日益严重的水资源危机使水稻的耐旱育种尤为迫切, 干旱环境下较高的植株水分含量有助于提高或维持作物产量的稳定性, 挖掘与耐旱性密切相关的分子标记有助于提高耐旱品种的选育效率。从供体Lemont (粳稻)导入到特青(籼稻)背景的254个高代回交导入系中筛选出覆盖供体全基因组的55个回交导入系, 采用PVC管栽培, 分析了干旱(胁迫)条件下水稻植株水分状况相关性状与籽粒产量、生物量的相关性并定位了相关QTL。研究表明, 植株水分相关性状(相对含水量、叶片水势、渗透势、卷叶度)均与籽粒产量显著相关。检测到7个相对含水量QTL, 7个叶片水势QTL, 5个渗透势QTL及5个卷叶QTL; 另检测到5个产量QTL, 7个生物量QTL。分析发现, 不仅QLwp5、QLr5、QRwc5和QY5同时分布在RM509~RM163区域, 且该区域还分布有对水分环境表现稳定的产量QTL(QGy5), 效应方向一致, 从遗传学角度解释了籽粒产量与水分相关性状之间的显著相关性。另外, QLr5、QRwc5、QY5、QLr2、QLr7、QLr8、QLr9、QRwc3、QRwc4a、QRwc12及QY7 等11个QTL曾在不同遗传背景群体中被检测到, 它们控制相同目标性状。研究认为RM509~RM163区域及QLr2、QLr7、QLr8、QLr9、QRwc3、QRwc4a、QRwc12和QY7所分布的染色体区域对水分环境或者遗传背景相对稳定, 在水稻分子标记辅助选择(MAS)耐旱育种实践中有较重要利用价值。     

Functional mechanisms of drought tolerance in maize through phenotyping and genotyping under well watered and water stressed conditions

Developing tolerant genotypes is crucial for stabilizing maize productivity under drought stress conditions as it is one of the most important abiotic stresses affecting crop yields. Twenty seven genotypes of maize (Zea mays L.) were evaluated for drought tolerance for three seasons under well watered and water stressed conditions to identify interactions amongst various tolerance traits and grain yield as well as their association with SSR markers. The study revealed considerable genetic diversity and significant variations for genotypes, environment and genotype × environment interactions for all the traits. The ranking of genotypes based on drought susceptibility index for morpho-physiological traits was similar to that based on grain yield and principal component analysis. Analysis of trait – trait and trait – yield associations indicated significant positive correlations amongst the water relations traits of relative water content (RWC), leaf water potential and osmotic potential as well as of RWC with grain yield under water stressed condition. Molecular analysis using 40 SSRs revealed 32 as polymorphic and 62 unique alleles were detected across 27 genotypes. Cluster analysis resulted in categorization of the genotypes into five distinct groups which was similar to that using principal component analysis. Based on overall performance across seasons tolerant and susceptible genotypes were identified for eventual utilization in breeding programs as well as for QTL identification. The marker-trait association analysis revealed significant associations between few SSR markers with water relations as well as yield contributing traits under water stressed conditions. These associations highlight the importance of functional mechanisms of intrinsic tolerance and cumulative traits for drought tolerance in maize.     

Detection of quantitative trait loci (QTLs) for seedling traits and drought tolerance in wheat using three related recombinant inbred line (RIL) populations

In order to detect quantitative trait loci (QTLs) for drought tolerance in wheat during seed germination conditional and unconditional QTL analyses of eight seedling traits were conducted under two water regimes using three related F₉ recombinant inbred line populations with a common female parent. A total of 87 QTLs for the eight seedlings traits and 34 specific QTLs related to drought tolerance were detected. Seventy-one of these QTLs were major QTLs with contributions to phenotypic variance of >10 %. Of the 34 QTLs related to drought tolerance only eight were also detected by unconditional analysis of seedling traits under osmotic stress conditions indicating that most of the QTLs related to drought tolerance could not be detected by unconditional QTL analysis. Therefore, conditional QTL analysis of stress-tolerance traits such as drought tolerance was feasible and effective. Of 11 important QTL clusters located on chromosomes 1BL, 1D, 2A, 2B, 2D, 4A, 6B, and 7B, nine were detected in multiple populations and eight were detected by both unconditional and conditional analyses.     

Detection of epistatic and environmental interaction QTLs for leaf orientation‐related traits in maize

Leaf architecture traits in maize are quantitative and have been studied by quantitative trait loci (QTLs) mapping. However, additional QTLs for these traits require mapping and the interactions between mapped QTLs require studying because of the complicated genetic nature of these traits. To detect common QTLs and to find new ones, we investigated the maize traits of leaf angle, leaf flagging‐point length, leaf length and leaf orientation value using a set of recombinant inbred line populations and single nucleotide polymorphism markers. In total, 19 QTLs contributed 4.13–13.52% of the phenotypic effects to the corresponding traits that were mapped, and their candidate genes are provided. Common and major QTLs have also been detected. All of the QTLs showed significant additive effects and non‐significant additive × environment effects in combined environments. The majority showed additive × additive epistasis effects and non‐significant QTL × environment effects under single environments. Common and major QTLs provided information for fine mapping and gene cloning, and SNP markers can be used for marker‐assisted selection breeding.     

Identification of quantitative trait loci for leaf‐related traits in an IBM Syn10 DH maize population across three environments

Leaf‐related traits (leaf length, leaf width, leaf area and leaf angle) are very important for the yield of maize (Zea mays L) due to their influence on plant type. Therefore, it is necessary to identify quantitative trait loci (QTLs) for leaf‐related traits. In this report, 221 doubled haploid lines (DHLs) of an IBM Syn10 DH population were provided for QTL mapping. In total, 54 QTLs were detected for leaf‐related traits in single environments using a high‐density genetic linkage map. Among them, only eight common QTLs were identified across two or three environments, and the common QTLs for the four traits explained 4.38%–19.99% of the phenotypic variation. qLL‐2‐1 (bin 2.09), qLW‐2‐2 (bin 2.09), qLW‐6‐3 (bin 6.07) and qLA‐5‐2 (bin 2.09) were detected in previous studies, and qLL‐1‐1, qLAr‐1‐1, qLAr‐2‐1 and qLA‐7‐1 may be new QTLs. Notably, qLW‐6‐3 and qLA‐5‐2 were found to be major QTLs explaining 19.99% and 10.96% of the phenotypic variation, respectively. Interestingly, we found three pairs of QTLs (qLW‐2‐2 and qLAr‐2‐1, qLW‐8‐1 and qLL‐8‐2, qLL‐3‐3 and qLAr‐3‐3) that control different traits and that were located on the same chromosome or in a nearby location. Moreover, nine pairs of loci with epistatic effects were identified for the four traits. These results may provide the foundation for QTL fine mapping and for an understanding of the genetic basis of variation in leaf‐related traits.     

在干旱和正常水分条件下玉米穗部性状QTL分析

穗部性状与产量密切相关,因此对其进行遗传剖析可为玉米高产育种提供理论基础,尤其是对干旱胁迫下的稳产有重要意义。本研究以玉米骨干亲本黄早四分别与自交系掖478和齐319进行杂交,构建了两套F_2:3群体(分别记为Y/H和Q/H)。在正常水分灌溉和干旱胁迫下对穗长、穗粗、轴粗、穗行数、行粒数、穗粒重和穗重等7个穗部性状进行了表型鉴定,采用基于混合线性模型的单环境分析和相同处理水平的联合分析方法进行了QTL分析。结果表明,在干旱胁迫下,2个群体的亲本及F_2:3家系的各性状值均低于正常水分条件,且穗粒重与穗长、穗重、穗粗呈正相关。在干旱胁迫下和正常水分条件下,通过两种检测方法共定位到75个玉米穗部性状QTL,其中Y/H群体共定位了20个QTL,分布在第1、第2、6、第5、第7、第10染色体上;Q/H群体共定位了55个QTL,分布在第2、第3、第4、第5、第6、第7、第9、第10染色体上;但是在干旱条件下两群体分别只检测到4个和19个QTL,明显低于正常水分条件下检测到的QTL数目。通过联合分析只检测到3个QTL与环境发生显著互作和6对QTL存在上位性互作效应,说明玉米穗部性状的遗传基础较为复杂。同时还发现,Y/H群体在正常灌溉与干旱条件下检测到2个一致性的QTL,分别是qKRE1-5-1和qKRE1-7-1,对表型变异解释的变化范围是6.15%~19.48%;Q/H群体检测到3个一致性QTL,分别是qKRE2-5-1、qGW2-10-1和qKRE2-3-1,对表型变异解释的变化范围是7.14%~16.65%,说明这些QTL受环境影响较小,能够稳定遗传,可以作为分子标记辅助选择的候选区间应用于玉米穗部性状抗旱性改良。     

不同密度下玉米穗部性状的QTL分析

为研究玉米穗部性状对不同种植密度的遗传响应,以郑58和HD568为亲本构建的220个重组自交系群体为材料,于2014年春、2014年冬及2015年春分别在北京和海南进行3个种植密度的田间试验,调查玉米穗长、穗粗、穗行数和行粒数等表型性状。利用SAS软件计算穗部性状的最优线性无偏估计值(BLUP),并采用完备区间作图法进行QTL定位。结果表明,在3个种植密度下共检测到42个QTL,单个QTL可解释4.20%~14.07%的表型变异。3个种植密度下同时检测到位于第2染色体上控制穗行数的QTL。2个种植密度下同时检测到4个与穗粗、穗行数和行粒数有关的QTL,其中第4染色体上1个与穗行数有关的主效QTL,在低、中种植密度下可分别解释表型变异的10.88%和14.07%。此外,在第2、4和9染色体上检测到3个同时调控不同穗部性状的QTL。研究结果表明玉米穗部性状在不同种植密度下的遗传调控发生变化,在不同密度下共同检测到的稳定QTL可应用于精细定位或开发玉米耐密性分子标记用于辅助育种。     

QTL mapping for seedling traits associated with low‐nitrogen tolerance using a set of advanced backcross introgression lines of rice

Nitrogen (N) deficiency is a major yield‐limiting factor in rice production. The objective of this study was to identify putative QTLs for low‐N stress tolerance of rice, using an advanced backcross population derived from crosses between an indica cultivar ‘93‐11’ and a japonica cultivar ‘Nipponbare’ and genotyped at 250 marker loci. Plant height, maximum root length, root dry weight, shoot dry weight and plant dry weight under two N conditions and their relative traits were used to evaluate low‐N tolerance at the seedling stage. A total of 44 QTLs were identified on chromosomes 1, 2, 3, 4, 5, 6, 8 and 9. Eight intervals on five chromosomes were identified to harbour multiple QTLs, suggesting pleiotropism or multigenic effects according to the contributor of alleles. Some QTL clusters were found in the nearby regions of genes associated with N recycling in rice, indicating that the key N metabolism genes might have effects on the expression of QTLs. Several unique QTLs for relative traits were detected, which suggested the specific genetic basis of relative performance.     

Mapping of QTL associated with waterlogging tolerance and drought resistance during the seedling stage in oilseed rape (Brassica napus)

Soil waterlogging and drought are major environmental stresses that suppress rapeseed (Brassica napus) growth and yield. To identify quantitative trait loci (QTL) associated with waterlogging tolerance and drought resistance at the rapeseed seedling stage, we generated a doubled haploid (DH) population consisting of 150 DH lines from a cross between two B. napus lines, namely, line No2127-17 × 275B F₄ (waterlogging-tolerant and drought-resistant) and line Huyou15 × 5900 F₄ (waterlogging-sensitive and drought-sensitive). A genetic linkage map was constructed using 183 simple sequence repeat and 157 amplified fragment length polymorphism markers for the DH population. Phenotypic data were collected under waterlogging, drought and control conditions, respectively, in two experiments. Five traits (plant height, root length, shoot dry weight, root dry weight and total dry weight) were investigated. QTL associated with the five traits, waterlogging tolerance coefficient (WTC) and drought resistance coefficient (DRC) of all the traits were identified via composite interval mapping, respectively. A total of 28 QTL were resolved for the five traits under control conditions, 26 QTL for the traits under waterlogging stresses and 31 QTL for the traits under drought conditions. Eleven QTL were detected by the WTC, and 19 QTL related to DRC were identified. The results suggest that the genetic bases of both waterlogging tolerance and drought resistance are complex. Some of the QTL for waterlogging tolerance-related traits overlapped with QTL for drought resistance-related traits, indicating that the genetic bases of waterlogging tolerance and drought resistance in the DH population were related in some degree.     

毛棉苗期抗旱性状的QTL定位

【目的】通过分析毛棉苗期抗旱相关性状的数量性状位点(Quantitative trait locus,QTL),以期检测稳定的主效QTL,促进栽培品种抗旱性状遗传改良及提高抗旱育种效率。【方法】以四倍体野生种毛棉(Gossypium tomentosum)和陆地棉品种中棉所12(CCRI 12)的种间杂种F2及其F2:3家系为研究材料,用于基因型分型的F2有188个系,用于表型分型的F2:3家系有149个株系。分别在干旱胁迫和正常灌水2个环境下调查表型数据。采用复合区间作图法对F2:3家系苗期相关性状抗旱系数进行QTL定位。【结果】对苗期相关性状抗旱系数的QTL定位分析,共得到16个QTL,其中与株高、叶片数、叶绿素含量、脯氨酸含量、丙二醛含量抗旱系数相关的QTL分别有5个、1个、3个、3个、4个,分布在13条染色体上。来自毛棉的5个加性QTL分别为qSHDC-19-1、qSHDC-19-2、qSLNDC-5-1、qMDADC-24-1、qMDADC-24-2,其加性效应值为0.10~0.22,解释变异9.4%~25.8%。【结论】这些与抗旱相关的QTL有助于棉花抗旱分子标记辅助选择。     

Gene action controlling yield and yield‐related traits among tef (Eragrostis tef [Zucc.] Trotter) populations under drought‐stressed and nonstressed conditions

This study was aimed to determine gene action for grain yield and yield‐related traits of newly developed tef populations under drought‐stressed and nonstressed conditions to improve drought tolerance. Ten crosses, along with the parents, were evaluated in the F₂ generation under drought‐stressed conditions at Hastebo and Adigdad sites in 2015 and Dura site in 2016 and under nonstressed conditions at Dura site in 2016. Additive gene action predominantly controlled the inheritance of the grain yield and majority of the yield‐related traits under drought‐stressed and nonstressed conditions. Under both test conditions, the genotypes DZ‐Cr‐387 and 9415 were the best general combiners for increased grain yield and morphological traits. Conversely, genotype 222076 was the best general combiner for reduced maturity period only. The selected parents are novel genetic materials for tef breeding programmes to improve grain yield and morphological traits with reduced days to maturity for drought tolerance breeding. The family of the cross DZ‐Cr‐387 × 222076 was selected for high grain yield and early maturity in both the drought‐stressed and nonstressed environments.     

Identification of QTLs controlling rice drought tolerance at seedling stage in hydroponic culture

‘Drought avoidance’ and ‘drought tolerance’ are two mechanisms by which plants adapt under water stress. These mechanisms are difficult to evaluate separately in field experiments. Using hydroponic culture, we studied the genetic control of drought tolerance in rice (Oryza sativa L.) without the effect of drought avoidance. A backcross inbred population of ‘Akihikari’ (lowland cultivar) × ‘IRAT109’ (upland cultivar) with 106 lines was cultured with (stressed condition) and without (non-stressed condition) polyethylene glycol (PEG) at seedling stage. The relative growth rate (RGR), specific water use (SWU), and water use efficiency (WUE) showed significant genotype × environment interactions with or without PEG, indicating that each line responded differently to water stress. A quantitative trait locus (QTL) analysis revealed that these interactions were QTL specific. A total of three QTLs on chromosomes 2, 4, and 7 were detected for RGR. The QTL on chromosome 7 had a constant effect across environments, while the QTL on chromosome 4 had an effect only under non-stressed condition and that on chromosome 2 only under stressed condition. The stress-specific QTL on chromosome 2 was not co-located with any QTLs for root system depth previously reported from the same mapping population. However, this QTL was co-located with a stress-specific QTL for SWU, suggesting that the control of transpiration was relevant to dry matter production under drought. We concluded that PEG-treated hydroponic culture is very effective for use in genetic analyses of drought tolerance at seedling stage.     

不同水分环境下玉米产量构成因子及籽粒相关性状的QTL分析

干旱胁迫对玉米产量及其相关性状有重要影响。本研究以我国玉米育种骨干亲本齐319和掖478分别和黄早四组配构建的两个F_2:3群体为材料,应用逐步联合分析的QTL定位方法,剖析新疆不同水分环境下(包含水区和旱区)玉米产量构成因子及籽粒相关性状的遗传基础。结果表明,在相同水分处理不同年份间产量构成因子和籽粒相关性状超过70%的QTL可稳定表达,旱区QTL的稳定性明显低于水区,当全部环境联合分析时,各性状QTL稳定性呈现一定程度的降低,但超过60%的QTL仍然稳定表达。两群体中共检测到11个环境钝感的主效QTL(在2个以上环境中检测到,且至少在一个环境下的贡献率大于10%),分布在bin1.10、2.00、4.09、7.02、9.02、10.04和10.07共7个基因组区段上,除bin10.04外所有环境钝感的主效QTL在全部环境下稳定表达。因此,玉米产量构成因子和籽粒相关性状的QTL在新疆相同水分处理不同年份间,甚至不同水分条件下大部分均可稳定表达,这些主效QTL位点可为抗旱分子育种和进一步精细定位提供参考。     

Relationships between leaf morpho‐anatomy,water status and cell membrane stability in leaves of wheat seedlings subjected to severe soil drought

The impact of the genotype‐specific leaf morphological and anatomical characteristics on the ability of wheat plants to preserve leaf water balance and cell membranes stability under drought stress was investigated. Seedlings of six modern semi‐dwarf (carriers of Rht, Reduced height genes) and six old tall bread wheat varieties were subjected to soil drought by withholding watering for 6 days. Morpho‐anatomical traits (leaf area, perimeter, thickness, stomata and trichome density) of daily watered (control) plants were characterized by light microscopy, scanning and image analyses. The leaf water status in both control and stressed plants was determined by measuring the relative water content (RWC). The leaf cell membranes stability in stressed plants was estimated by conductometric determination of the membranes injury index. On average, the modern semi‐dwarf varieties had less leaf area and leaf perimeter, and less dissection index, a parameter characterizing the leaf shape. Under drought stress, the modern genotypes maintained better water balance evidenced by significantly higher leaf RWC and better‐preserved the cell membranes stability supported by significantly lower Injury index. The correlations between morpho‐anatomical traits in control plants and drought tolerance‐related traits showed that the higher the leaf dissection index (i.e. more oblong leaves), the greater the water loss and the leaf membrane damages after desiccation were. The effect of shape of the evaporating surface on the water loss was modelled using wet filter paper. Similar to plant leaves, the evaporation and, respectively, water loss from paper pieces of more oblong shape (i.e. higher dissection index) was more intensive. The elucidation of the impact of the leaf shape on transpiration might contribute to better understanding of the mechanisms used by plants to maintain water reserves during drought stress and could be a basis for developing of simple and fast screening methods aiding the selection of drought tolerant genotypes.     

Mapping the QTLs underlying drought stress at developmental stage of sorghum (Sorghum bicolor (L.) Moench) by association analysis

This study was conducted to identify quantitative trait loci (QTLs) for drought tolerance in sorghum (Sorghum bicolor (L.) Moench) by association mapping using a simple sequence repeat (SSR)-marker-based diversity research set. Genotypic data for 98 SSR marker loci on ten chromosomes were used for the association analysis. The experiment was conducted under control (well-watered) and drought stress conditions, and the phenotypic values of 23 morphological traits were recorded. Drought tolerance was assessed by using a leaf drying score as a parameter of the tolerance/susceptibility: scores were assigned on a scale from 1 (most tolerant) to 9 (most susceptible). Under the control conditions, 17 QTLs associated with 12 traits were identified on chromosomes 1, 2, 4, 8, 9, and 10, with ?Log₁₀ (P) ranging from 2.5 to 7.6 and explaining 9.5–57.5 % of the total phenotypic variance for the traits. Under the drought stress conditions, nine QTLs associated with 8 traits were identified on chromosomes 1, 2, 3, and 10 that explained 9–61.2 % of the total phenotypic variance for the traits, with ?Log₁₀ (P) ranging from 2.5 to 3.5. QTLs for some traits were detected only under the drought stress condition, suggesting that these traits are important in drought tolerance. These QTLs could be used to further dissect the genetic and physiological basis of drought tolerance in sorghum.