Identification of quantitative trait loci controlling developmental characteristics of Brassica oleracea L

A segregating population of F₁-derived doubled haploid (DH) lines of Brassica oleracea was used to detect and locate QTLs controlling 27 morphological and developmental traits, including leaf, flowering, axillary bud and stem characters. The population resulted from a cross between two very different B. oleracea crop types, an annual cauliflower and a biennial Brussels sprout. A principal component analysis (PCA), based on line means, allowed all the traits to be grouped into distinct categories according to the first five Principal Components. These were: leaf traits (PC1), flowering traits (PC2), axillary bud traits (PC3 and 5) and stem traits (PC4). Between zero and four putative QTL were located per trait, which individually explained between 6% and 43% of the additive genetic variation, using the multiple-marker regression approach to QTL mapping. For lamina width, bare petiole length and stem length two QTL with opposite effects were detected on the same linkage groups. Intra- and inter-specific comparative mapping using RFLP markers identified a QTL on linkage group O8 accounting for variation in vernalisation, which is probably synonymous with a QTL detected on linkage group N19 of Brassica napus. In addition, a QTL for petiole length detected on O3 of this study appeared to be homologous to a QTL detected on another B. oleracea genetic map (Camargo et al. 1995). Received: 28 March 2001 / Accepted: 25 June 2001     

Quantitative genetic variation of leaf size and shape in a mixed diploid and triploid population of Populus

In the interspecific cross of Populus trichocarpa x P. deltoides, unexpected simultaneous occurrence of diploid hybrids and triploid hybrids (with two alleles from the female parent and one from the male parent at each locus) led us to examine the evolutionary genetic significance of this phenomenon. As expected, leaf size and shape of the triploid progeny are closer to the female P. trichocarpa than male P. deltoides parent. Although the pure triploid progeny population did not have higher genetic variance in leaf traits than the pure diploid population, the former appears to hide much non-additive genetic variance and display strong genetic control over the phenotypic plasticity of leaf traits. It is suggested that the cryptic non-additive variance, especially epistasis, can be released when a population is disturbed by changes in the environment. A mixed diploid and triploid progeny population combines phenotypic and genetic characteristics of both pure hybrids and is considered to be of adaptive significance for populars to survive and evolve in a fluctuating environment. The significant effect due to general and specific combining ability differences at the population level suggests that the population divergence of these two species is under additive and non-additive genetic control.     

The genetics and genomics of the drought response in Populus

The genetic nature of tree adaptation to drought stress was examined by utilizing variation in the drought response of a full-sib second generation (F(2)) mapping population from a cross between Populus trichocarpa (93-968) and P. deltoides Bart (ILL-129) and known to be highly divergent for a vast range of phenotypic traits. We combined phenotyping, quantitative trait loci (QTL) analysis and microarray experiments to demonstrate that 'genetical genomics' can be used to provide information on adaptation at the species level. The grandparents and F(2) population were subjected to soil drying, and contrasting responses to drought across genotypes, including leaf coloration, expansion and abscission, were observed, and QTL for these traits mapped. A subset of extreme genotypes exhibiting extreme sensitivity and insensitivity to drought on the basis of leaf abscission were defined, and microarray experiments conducted on these genotypes and the grandparent species. The extreme genotype groups induced a different set of genes: 215 and 125 genes differed in their expression response between groups in control and drought, respectively, suggesting species adaptation at the gene expression level. Co-location of differentially expressed genes with drought-specific and drought-responsive QTLs was examined, and these may represent candidate genes contributing to the variation in drought response.     

Novel pleiotropic loci controlling panicle architecture across environments in japonica rice （Oryza sativa L.）

To identify quantitative trait loci (QTLs) controlling panicle architecture in japonica rice, a genetic map was constructed based on simple sequence repeat (SSR) markers and 254 recombinant inbred lines (RILs) derived from a cross between cultivars Xiushui 79 and C Bao. Seven panicle traits were investigated under three environments. Single marker analysis indicated that a total of 27 SSR markers were highly associated with panicle traits in all the three environments. Percentage of phenotypic variation explained by single locus varied from 2% to 35%. Based on the mixed linear model, a total of 40 additive QTLs for seven panicle traits were detected by composite interval mapping, explaining 1.2%-35% of phenotypic variation. Among the 9 QTLs with more than 10% of explained phenotypic variation, two QTLs were for the number of primary branches per panicle (NPB), two for panicle length (PL), two for spikelet density (SD), one for the number of secondary branches per panicle (NSB), one for secondary branch distribution density (SBD), and one for the number of spikelets per panicle (NS), respectively. qPLSD-9-1 and qPLSD-9-2 were novel pleiotropic loci, showing effects on PL and SD simultaneously. qPLSD-9-1 explained 34.7% of the phenotypic variation for PL and 25.4% of the phenotypic variation for SD, respec- tively. qPLSD-9-2 explained 34.9% and 24.4% of the phenotypic variation for PL and SD, respectively. The C Bao alleles at the both QTLs showed positive effects on PL, and the Xiushui 79 alleles at the both QTLs showed positive effects on SD. Genetic variation of panicle traits are mainly attributed to additive effects. QTL × environment interactions were not significant for additive QTLs and additive × additive QTL pairs.     

Genetic architecture of quantitative trait loci associated with morphological and agronomic trait differences in a wild by cultivated barley cross.

Hordeum vulgare subsp. spontaneum is the progenitor of cultivated barley (Hordeum vulgare L.). Domestication combined with plant breeding has led to the morphological and agronomic characteristics of modern barley cultivars. The objective of this study was to map the genetic factors that morphologically and agronomically differentiate wild barley from modern barley cultivars. To address this objective, we identified quantitative trait loci (QTLs) associated with plant height, flag leaf width, spike length, spike width, glume length in relation to seed length, awn length, fragility of ear rachis, endosperm width and groove depth, heading date, flag leaf length, number of tillers per plant, and kernel color in a Harrington/OUH602 advanced backcross (BC2F8) population. This population was genotyped with 113 simple sequence repeat markers. Thirty QTLs were identified, of which 16 were newly identified in this study. One to 4 QTLs were identified for each of the traits except glume length, for which no QTL was detected. The portion of phenotypic variation accounted for by individual QTLs ranged from about 9% to 54%. For traits with more than one QTL, the phenotypic variation explained ranged from 25% to 71%. Taken together, our results reveal the genetic architecture of morphological and agronomic traits that differentiate wild from cultivated barley.     

优良单株家系辣木叶的表型性状分析

为挖掘辣木(Moranga oleifera)优良种质资源,对30个优良单株家系的叶片表型性状进行研究。结果表明,除叶形外,辣木不同家系间的叶柄和叶片颜色、复叶数、复叶柄长度和直径、复叶间距、叶长、叶宽均存在不同程度的差异。复叶数与复叶柄长度和直径、复叶间距、叶长、叶宽呈极显著正相关;主成分分析表明,叶长、叶宽、复叶柄长度和直径、复叶间距、叶柄和叶片颜色是区分辣木不同家系最主要的叶片性状指标。聚类分析结果表明,30个辣木家系可分为3大类,叶片表型性状存在显著差异的家系的遗传距离较远。因此,叶柄和叶片颜色、复叶数、复叶柄长度和直径、复叶间距、叶长、叶宽将为直观区分辣木家系提供参考。     

Identification and mode of action of quantitative trait loci affecting seedling height and leaf area in Eucalyptus nitens

 Regions of the genome influencing height and leaf area in seedlings of a three-generation outbred pedigree of Eucalyptus nitens have been identified. Three QTLs affecting height and two QTLs affecting leaf area were located using single-factor analysis of variance. The three QTLs affecting height each explained between 10.3 and 14.7% of the phenotypic variance, while the two QTLs for leaf area each explained between 9.8 and 11.6% of the phenotypic variation. Analysis of fully informative marker loci linked to the QTLs enabled the mode of action of the QTLs to be investigated. For three loci the QTL effect segregated from only one parent, while for two loci the QTL showed multiple alleles and the effect segregated from both parents in the pedigree. The two QTLs affecting leaf area were located in the same regions as two of the QTLs affecting height. Analysis of these regions with fully informative markers showed that both QTLs were linked to the same markers, but one had a similar size of effects and a similar mode of action for both height and leaf area, whilst the other showed a different mode of action for the two traits. These regions may contain two closely linked genes or may involve a single gene with a pleiotrophic effect on both height and leaf area. The QTL with the greatest effect showed multiple alleles and an intra-locus interaction that reduced the size of the effect. Assessment for two of the QTLs in a second related family did not show an effect associated with the marker loci; however, this was consistent with the mode of action of these QTLs and the pattern of inheritance in the second family. Received: 1 August 1996 / Accepted: 25 October 1996     

大白菜部分形态性状的QTL定位与分析

应用352个标记位点的大白菜AFLP和RAPD图谱和一套栽培品种间杂交获得的重组自交系群体,采用复合区间作图的方法对大白菜9个形态性状进行QTL定位及遗传效应研究。在14个连锁群上检测到50个QTL:其中控制株型的QTL有5个;控制株高的QTL有6个;控制开展度的QTL有5个;控制最大叶长的QTL有7个;控制最大叶宽的QTL有4个;控制叶形指数的QTL有6个;控制中肋长的QTL有7个;控制中肋宽的QTL有4个;控制抽苔的QTL有6个。另外,估算了单个QTL的遗传贡献率和加性效应。这将为大白菜品种改良中形态性状的分子标记辅助选择提供理论依据。     

Quantitative trait loci for yield components in oil palm (Elaeis guineensis Jacq.)

The development of an oil palm RFLP marker map has enabled marker-based QTL mapping studies to be undertaken. Information from 153 RFLP markers was used in combination with phenotypic data from an F₂ population to estimate the position and effects of quantitative trait loci (QTLs) for traits including yield of fruit and its components and measures of vegetative growth. The mapping population consisted of 84 palms segregating for the major gene influencing shell thickness. Marker data were analysed to produce a linkage map consisting of 22 linkage groups. The QTL mapping analysis was carried out by interval mapping and single-marker analysis for the unlinked markers; significance thresholds were generated by permutation. Using both single-marker and interval-mapping analysis significant marker associated QTL effects were found for 11 of the 13 traits analysed. The results of interval-mapping analysis of fruit weight, petiole cross section and rachis length, and ratios of shell:fruit, mesocarp:fruit and kernel:fruit indicated significant (P<0.05) QTLs at the genome-wide threshold. The putative QTLs were associated with between 8.2% and 44.0% of the phenotypic variation, with an average of 27% for the single-marker analysis and 19% for the interval-mapping analysis. The higher percentage of phenotypic variation explained in the single-marker analysis, when compared to the interval-mapping analysis, is likely to be due to the lower stringency associated with the single-marker analysis. Large dominance deviations were associated with a sizeable proportion of the putative QTLs. The ultimate objective of mapping QTLs in commercial populations is to utilise novel breeding strategies such as marker-assisted selection (MAS). The potential impact of MAS in oil palm breeding programmes is discussed. Received: 26 June 2000 / Accepted: 24 October 2000     

Mapping Quantitative Trait Loci for Grain Appearance Traits of Rice Using a Recombinant Inbred Line Population

A linkage map consisting of 221 markers was constructed based on a recombinant inbred line (RIL) population from the cross between Zhenshan 97 and Minghui 63. Quantitative trait loci (QTL) mapping was carried out for grain appearance traits such as grain length, grain width and grain shape in rice in 1998 and 1999. Based on interval mapping method at the threshold LOD≥2.4, six, two and two QTLs were detected for grain length, grain width and grain shape, respectively, in 1998; In 1999, three, two and two QTLs were identified for the three traits, respectively. Of them, seven QTLs were simultaneously identified in both of the years. The QTL with large effects located in the interval RG393-C1087 on chromosome 3 not only controlled the grain length, but also influenced the grain shape. It explained 57.5%, 61.4% and 26.7%, 29.9% of phenotypic variation of the grain length and the grain shape in two years, respectively. The QTL with large effects located in the interval RG360-C734B on chromosome 5 affected the grain width and the grain shape. It explained 44.2%, 53.2% and 32.1%, 36.0% of phenotypic variation of the grain width and the shape in two years, respectively. Eight, five and five QTLs were identified for the grain length, width and shape, respectively, based on mixed linear-model composite interval mapping method at P =0.005. Their general contributions were 58.81%, 44.75%, and 57.47%. One QTL for the grain length was found to be significant interaction with environment.     

Individual‐level leaf trait variation and correlation across biological and spatial scales

Even with increasing interest in the ecological importance of intraspecific trait variation (ITV) for better understanding ecological processes, few studies have quantified ITV in seedlings and assessed constraints imposed by trade‐offs and correlations among individual‐level leaf traits. Estimating the amount and role of ITV in seedlings is important to understand tree recruitment and long‐term forest dynamics. We measured ten different size, economics, and whole leaf traits (lamina and petiole) for more than 2,800 seedlings (height ≥ 10 cm and diameter at breast height < 1 cm) in 283 seedling plots and then quantified the amount of ITV and trait correlations across two biological (intraspecific and interspecific) and spatial (within and among plots) scales. Finally, we explored the effects of trait variance and sample size on the strength of trait correlations. We found about 40% (6%–63%) variation in leaf‐level traits was explained by ITV across all traits. Lamina and petiole traits were correlated across biological and spatial scales, whereas leaf size traits (e.g., lamina area) were weakly correlated with economics traits (e.g., specific lamina area); lamina mass ratio was strongly related to the petiole length. Trait correlations varied among species, plots, and different scales but there was no evidence that the strength of trait relationships was stronger at broader than finer biological and spatial scales. While larger trait variance increased the strength of correlations, the sample size was the most important factor that was negatively related to the strength of trait correlations. Our results showed that a large amount of trait variation was explained by ITV, which highlighted the importance of considering ITV when using trait‐based approaches in seedling ecology. In addition, sample size was an important factor that influenced the strength of trait correlations, which suggests that comparing trait correlations across studies should consider the differences in sample size.     

Molecular Genetics of Growth and Development in Populus. IV. Mapping Qtls with Large Effects on Growth, Form, and Phenology Traits in a Forest Tree

We have mapped quantitative trait loci (QTLs) for commercially important traits (stem growth and form) and an adaptive trait (spring leaf flush) in a Populus F(2) generation derived from a cross between interspecific F(1) hybrids (P. trichocarpa X P. deltoides). Phenotypic data were collected over a 2-year period from a replicated clonal trial containing ramets of the parental, F(1), and F(2) trees. Contrary to the assumptions of simple polygenic models of quantitative trait inheritance, 1-5 QTLs of large effect are responsible for a large portion of the genetic variance in each of the traits measured. For example, 44.7% of the genetic variance in stem volume after 2 years of growth is controlled by just two QTLs. QTLs governing stem basal area were found clustered with QTLs for sylleptic branch leaf area, sharing similar chromosomal position and mode of action and suggesting a pleiotropic effect of QTLs ultimately responsible for stem diameter growth.     

QTL mapping of flag leaf-related traits in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Key message

QTL controlling flag leaf length, flag leaf width, flag leaf area and flag leaf angle were mapped in wheat.

Abstract

This study aimed to advance our understanding of the genetic mechanisms underlying morphological traits of the flag leaves of wheat (Triticum aestivum L.). A recombinant inbred line (RIL) population derived from ND3331 and the Tibetan semi-wild wheat Zang1817 was used to identify quantitative trait loci (QTLs) controlling flag leaf length (FLL), flag leaf width (FLW), flag leaf area (FLA), and flag leaf angle (FLANG). Using an available simple sequence repeat genetic linkage map, 23 putative QTLs for FLL, FLW, FLA, and FLANG were detected on chromosomes 1B, 2B, 3A, 3D, 4B, 5A, 6B, 7B, and 7D. Individual QTL explained 4.3–68.52% of the phenotypic variance in different environments. Four QTLs for FLL, two for FLW, four for FLA, and five for FLANG were detected in at least two environments. Positive alleles of 17 QTLs for flag leaf-related traits originated from ND3331 and 6 originated from Zang1817. QTLs with pleiotropic effects or multiple linked QTL were also identified on chromosomes 1B, 4B, and 5A; these are potential target regions for fine-mapping and marker-assisted selection in wheat breeding programs.

     

两个水稻骨干恢复系重要农艺性状的遗传基础研究

水稻骨干恢复系是指在杂交稻育种中广泛应用的一类恢复系。探明骨干恢复系的遗传基础,发掘其重要农艺性状基因/QTL,对分子标记辅助选择水稻恢复系育种具有重要应用价值。本研究以生产上广泛应用的三系骨干恢复系成恢727和两系骨干恢复系9311为亲本,培育了具有250个系的重组自交系群体。分别在2015年三亚和2016年合肥两个环境下进行了9个重要农艺性状表型和SSR分子标记基因型鉴定,用SAS9.2分析表型数据,用QTL Ici Mapping v4.1进行QTL定位分析。在三亚和合肥两个环境下共检测到39个QTL,三亚检测到16个,分布于第1、2、4、7、8、10、11和12染色体上;合肥检测24个,分布于第1、2、3、7、8、9、10和12染色体上。其中qPH1-1在三亚和合肥两个环境下都能检测到,加性效应分别为-1.75和-2.46。在检测到的39个QTL中,有24个QTL的增效等位基因来自恢复系成恢727,15个QTL的增效等位基因来自9311。共计有26个QTL曾被前人定位,13个属于尚未见文献报道的新QTL。另外,在RM279~RM521、RM336~RM3534、RM25~RM547、RM553~RM160、RM222~RM271区段内检测到5个多效性QTL位点。其中RM25~RM547位点与已经克隆的基因Ghd8位置相近。RM553~RM160位点是一个新的多效性位点,分别控制每穗实粒数、单株产量和结实率,而且效应和表型变异贡献率都较大。其余3个位点在前人的研究中分别有所报道,但其多效性则是在本研究中首次发现。在本研究新发掘到的QTL中,控制穗数的QTL qPN12-1,控制穗长的QTL qPL1-2和qPL10-1,控制总粒数的QTL qSNP2-1和qSNP10-1,控制结实率的QTL qSF3-1,控制千粒重QTL qTGW7-1和控制产量的QTL qGY1-1效应均比较大,解释的表型遗传变异比例也较高。本研究的结果将会为相关性状QTL的精细定位、克隆和育种应用奠定基础。     

Quantitative trait locus analysis of multiple agronomic traits in the model legume Lotus japonicus.

The first quantitative trait locus (QTL) analysis of multiple agronomic traits in the model legume Lotus japonicus was performed with a population of recombinant inbred lines derived from Miyakojima MG-20 x Gifu B-129. Thirteen agronomic traits were evaluated in 2004 and 2005: traits of vegetative parts (plant height, stem thickness, leaf length, leaf width, plant regrowth, plant shape, and stem color), flowering traits (flowering time and degree), and pod and seed traits (pod length, pod width, seeds per pod, and seed mass). A total of 40 QTLs were detected that explained 5%-69% of total variation. The QTL that explained the most variation was that for stem color, which was detected in the same region of chromosome 2 in both years. Some QTLs were colocated, especially those for pod and seed traits. Seed mass QTLs were located at 5 locations that mapped to the corresponding genomic positions of equivalent QTLs in soybean, pea, chickpea, and mung bean. This study provides fundamental information for breeding of agronomically important legume crops.     

麻栎不同种源的表型性状变异分析

以来源于广西、广东、贵州、湖南、浙江、安徽、江苏、湖北、四川、陕西、河南和山东的28个麻栎（QuercusacutissimaLinn.）地理种源为研究对象,分析了6个表型性状（包括叶长、叶宽、叶柄长和叶长宽比4个叶片性状及株高和地径2个生长性状）的变异状况;研究了种源间及种源内各性状的变异系数（CV）和相对极差（R°）及种源间各叶片性状的表型分化系数（Vst）;并进行了各性状的相关性分析及主成分分析;此外,还对28个种源进行了聚类分析。结果表明：各种源间6个表型性状均有极显著差异（P〈0.01）;而种源内仅叶宽和叶长分别具有极显著和显著（P〈0.05）差异。种源间4个叶片性状的Vst平均值为23.98%,其中叶宽的Vst值最大（42.39%）。在6个表型性状中,叶柄长的CV平均值最大（33.60%）、地径的CV平均值最小（16.25%）;在不同种源中,陕西汉中种源各性状的CV平均值最小（14.39%）,而江苏句容、四川万源和山东沂水种源各性状的CV平均值均超过30%。各种源间表型性状的R°值差异明显,其中,四川万源种源的R°值最大（60.99%）,湖南新宁和陕西汉中种源的R°值较小（30%以下）;而6个性状间R°值差别不大,为34.93%-44.98%,表明麻栎种源间的极端差异程度有明显不同,而表型性状间的极端差异程度差异不大。4个叶片性状中,仅叶宽与叶长宽比呈极显著负相关,其他性状间均呈极显著正相关;叶片性状与生长性状间均呈负相关,而株高与地径则呈极显著正相关。麻栎种源表型性状变异的第1和第2主成分的贡献率分别为43.663%和27.695%,第1主成分中叶性状变异占主导地位,而第2主成分则主要反映生长性状的变异。通过聚类分析可将28个种源分为2大类,分别包含22和6个种源,但聚类分析结果与其地理分布没有明显相关性。研究结果显示：麻栎?     

Quantitative Trait Loci Mapping for Leaf Length and Leaf Width in Rice cv. IR64 Derived Lines

The present study was conducted to identify quantitative trait loci (QTLs) for leaf size traits in IR64 introgression lines (INLs). For this purpose, selected F2 populations derived from crosses between recurrent parent IR64 and its derived INLs, unique for leaf length and leaf width, were used to confirm QTLs. A total of eight QTLs, mapped on three chromosomes, were identified for the four leaf size traits in six F2 populations. A QTL for leaf length, qLLnpt-1, in HKL69 was identified around simple sequence repeat (SSR) marker RM3709 on chromosome 1. Two QTLs for flag leaf length, qFLLnpt-2 and qFLLnpt-4, in HFG39 were indentified on chromosomes 2 and 4, respectively. For flag leaf width, a QTL, qFLWnpt-4, in HFG39 was identified around RM17483 on chromosome 4. While another QTL for flag leaf width, qFLWnpt-1, in HFG27 was identified around RM3252 on chromosome 1. A QTL for leaf width, qLWnpt-2, in HKL75 was identified around RM7451 on chromosome 2. For leaf width, two QTLs, qLWnpt-4a, qLWnpt-4b, in HKL48 and HKL99 were identified around RM7208 and RM6909, respectively on chromosome 4. Results from this study suggest the possibilities to use marker-assisted selection and pyramiding these QTLs to improve rice water productivity.     

Genetic architecture of qualitative and quantitative Melampsora larici-populina leaf rust resistance in hybrid poplar: genetic mapping and QTL detection

In order to elucidate the genetic control of resistance to Melampsora larici-populina leaf rust in hybrid poplars, a Populus deltoides x P. trichocarpa F(1) progeny was analysed for qualitative and quantitative rust resistances. This progeny was evaluated for three components of quantitative resistance (latent period, uredinia number and uredinia size) to seven M. larici-populina strains in controlled conditions, and for one component of field susceptibility (rust colonization on the most infected leaf). One qualitative resistance locus inherited from P. deltoides, R(1), was localized on the genetic map. It segregates 1 : 1 in the F(1) progeny and is effective against four of the studied strains. QTL analysis was performed separately on R(1) and r(1) genotype subsets. An additional detection was conducted on the entire F(1) progeny for the three strains able to overcome R(1) and for MAX2. A total of nine QTLs were detected. Two had large, broad-spectrum effects. One (R(US)) is inherited from the P. trichocarpa parent; the other is inherited from P. deltoides and colocalized with R(1). Seven QTLs had only limited and specific effects. Significant interaction effects were detected mainly between the two major QTLs. Implications of these results for durable resistance breeding strategies, and possible benefits from the Populus genome sequence, are discussed.     

Comparative mapping of QTLs determining the plant size of Brassica oleracea

Quantitative trait loci (QTLs) influencing the size of leaves and stems were detected by restriction fragment length polymorphisms (RFLP) in three Brassica oleracea F₂ populations derived from crosses of rapid-cycling Brassica to three B. oleracea varieties, Cantanese, Pusa Katki and Bugh Kana. Morphological traits, including lamina length, lamina width, petiole length, stem length, stem width and node number were evaluated. A total of 47 QTLs were detected based on a LOD threshold of 2.5. Through comparative mapping we inferred that the 47 QTLs might reflect variation in as few as 35 different genetic loci, and 28 ancestral genes. For the trait of lamina length, we identified QTLs corresponding to five ancestral genes, which mapped near the locations corresponding to five known Arabidopsis mutations, rev, axr1, axr3, axr4 and as2. For the trait of stem length, we identified QTLs corresponding to five ancestral genes, which mapped near the locations corresponding to nine known Arabidopsis mutations, dw3, dw6, acl5, dw7, ga4, ga1, dw1, axr1 and axr3. The possibility of using Arabidopsis/Brassica as a model to extrapolate genetic information into other crops was examined. Received: 30 October 2000 / Accepted: 24 November 2000     

Elucidating genomic regions determining enhanced leaf growth and delayed senescence in elevated CO2

Limited information is available on the genetic variation and control for plant growth response to elevated CO(2) (e[CO(2)]). Such information is necessary to understand plant adaptation and evolution in future rising CO(2). Here, quantitative trait loci (QTL) for leaf growth, development, quality and leaf senescence were determined in a tree pedigree - an F(2) hybrid of Populus trichocarpa T. & G and Populus deltoides Marsh, following season-long exposure to either current day ambient carbon dioxide (a[CO(2)]) or e[CO(2)] at 600 microL L(-1). Leaf growth and development differed between the grandparents such that P. trichocarpa showed greater response to e[CO(2)]. In the F(2) generation, leaf development and quality traits including leaf area, leaf shape, epidermal cell area, and stomatal number, specific leaf area (SLA), and the phenology trait, canopy senescence index, were sensitive to e[CO(2)]. Sixty-nine QTL were mapped for the 19 traits of plants in a[CO(2)] while 60 QTL were mapped for plants in e[CO(2)]. The results suggest that although many QTL mapped to common positions in a[CO(2)] and e[CO(2)], confirming their importance in determining growth, there was also differential genetic control for a number of traits including leaf senescence. Candidate genes were shown to collocate to regions where response QTL mapped. This study is the first to identify candidate genes that may be important in determining plant adaptation to future high-CO(2) world.