Quantitative trait loci for performance traits in a broiler × layer cross

An F₂ resource population, derived from a broiler × layer cross, was used to map quantitative trait loci (QTL) for body weights at days 1, 35 and 41, weight gain, feed intake, feed efficiency from 35 to 41 days and intestinal length. Up to 577 F₂ chickens were genotyped with 103 genetic markers covering 21 linkage groups. A preliminary QTL mapping report using this same population focused exclusively on GGA1. Regression methods were applied to line-cross and half-sib models for QTL interval mapping. Under the line-cross model, eight QTL were detected for body weight at 35 days (GGA2, 3 and 4), body weight at 41 days (GGA2, 3, 4 and 10) and intestine length (GGA4). Under the half-sib model, using sire as common parent, five QTL were detected for body weight at day 1 (GGA3 and 18), body weight at 35 days (GGA2 and 3) and body weight at 41 days (GGA3). When dam was used as common parent, seven QTL were mapped for body weight at day 1 (GGA2), body weight at day 35 (GGA2, 3 and 4) and body weight at day 41 (GGA2, 3 and 4). Growth differences in chicken lines appear to be controlled by a chronological change in a limited number of chromosomal regions.     

Identification of quantitative trait loci for shank length and growth at different development stages in chicken

Shank length affects chicken leg health and longer shanks are a source of leg problems in heavy-bodied chickens. Identification of quantitative trait loci (QTL) affecting shank length traits may be of value to genetic improvement of these traits in chickens. A genome scan was conducted on 238 F₂ chickens from a reciprocal cross between the Silky Fowl and the White Plymouth Rock breeds using 125 microsatellite markers to detect static and developmental QTL affecting weekly shank length and growth (from 1 to 12 weeks) in chickens. Static QTL affected shank length from birth to time t , while developmental QTL affected shank growth from time t− 1 to time t . Seven static QTL on six chromosomes (GGA2, GGA3, GGA4, GGA7, GGA9 and GGA23) were detected at ages of 2, 3, 4, 5, 6, 7, 9 and 12 weeks, and six developmental QTL on five chromosomes (GGA1, GGA2, GGA4, GGA5 and GGA23) were detected for five shank growth periods, weeks 2–3, 4–5, 5–6, 10–11 and 11–12. A static QTL and a developmental QTL ( SQSL1 and DQSL2 ) were identified at GGA2 (between ADL0190 and ADL0152 ). SQSL1 explained 2.87–5.30% of the phenotypic variation in shank length from 3 to 7 weeks. DQSL2 explained 2.70% of the phenotypic variance of shank growth between 2 and 3 weeks. Two static and two developmental QTL were involved chromosome 4 and chromosome 23. Two chromosomes (GGA7 and GGA9) had static QTL but no developmental QTL and another two chromosomes (GGA1 and GGA5) had developmental QTL but no static QTL. The results of this study show that shank length and shank growth at different developmental stages involve different QTL.     

Identification of chromosomal regions associated with growth and carcass traits in an F3 full sib intercross line originating from a cross of chicken lines divergently selected on body weight

An F₃ resource population originating from a cross between two divergently selected lines for high (D+ line) or low (D− line) body weight at 8-weeks of age (BW55) was generated and used for Quantitative Trait Locus (QTL) mapping. From an initial cross of two founder F₀ animals from D(+) and D(−) lines, progeny were randomly intercrossed over two generations following a full sib intercross line (FSIL) design. One hundred and seventy-five genome-wide polymorphic markers were employed in the DNA pooling and selective genotyping of F₃ to identify markers with significant effects on BW55. Fifty-three markers on GGA2, 5 and 11 were then genotyped in the whole F₃ population of 503 birds, where interval mapping with GridQTL software was employed. Eighteen QTL for body weight, carcass traits and some internal organ weights were identified. On GGA2, a comparison between 2-QTL vs. 1-QTL analysis revealed two separate QTL regions for body, feet, breast muscle and carcass weight. Given co-localization of QTL for some highly correlated traits, we concluded that there were 11 distinct QTL mapped. Four QTL localized to already mapped QTL from other studies, but seven QTL have not been previously reported and are hence novel and unique to our selection line. This study provides a low resolution QTL map for various traits and establishes a genetic resource for future fine-mapping and positional cloning in the advanced FSIL generations.     

Genome-wide association analysis reveals cryptic alleles as an important factor in heterosis for fatness in chicken F2 population

Genome-wide association studies have become possible in the chicken because of the recent availability of the complete genome sequence, a polymorphism map and high-density single nucleotide polymorphism (SNP) genotyping platforms. We used these tools to study the genetic basis of a very high level of heterosis that was previously observed for fatness in two F₂ populations established by crossing one outbred broiler (meat-type) sire with dams from two unrelated, highly inbred, light-bodied lines (Fayoumi and Leghorn). In each F₂ population, selective genotyping was carried out using phenotypically extreme males for abdominal fat percentage (AF) and about 3000 SNPs. Single-point association analysis of about 500 informative SNPs per cross showed significant association ( P  < 0.01) of 15 and 24 markers with AF in the Broiler × Fayoumi and Broiler × Leghorn crosses respectively. These SNPs were on 10 chromosomes (GGA1, 2, 3, 4, 7, 8, 10, 12, 15 and 27). Interestingly, of the 39 SNPs that were significantly associated with AF, there were about twice as many homozygous genotypes associated with higher AF that traced back to the inbred lines alleles, although the broiler line had on average higher AF. These SNPs are considered to be associated with QTL with cryptic alleles. This study reveals cryptic alleles as an important factor in heterosis for fatness observed in two chicken F₂ populations, and suggests epistasis as the common underlying mechanism for heterosis and cryptic allele expression. The results of this study also demonstrate the power of high marker-density SNP association studies in discovering QTL that were not detected by previous microsatellite-based genotyping studies.     

Genetic architecture for hole-board behaviors across substantial time intervals in young, middle-aged and old mice

A quantitative trait locus (QTL) analysis of behaviors across the life span was conducted in F₂ mice from a C57BL/6J × DBA/2J cross and 22 BXD recombinant inbred (RI) strains. Mice of three age groups were tested in a hole-board apparatus for 3 min on three occasions ∼1 month apart (average age at test 150, 450 and 750 days, ∼400 mice per group, divided equally by sex). Quantitative trait loci with small effect size were found on 11 chromosomes for hole-board activity (Hbact) and hole-board rearing (Hbrear). Analysis of 22 RI strains tested at 150 and 450 days of age found only suggestive linkage, with four QTL for Hbact overlapping with those from the F₂ analysis. There was a significant phenotypic correlation between Hbact and Hbrear (∼0.55–0.69) and substantial commonality among QTL for the two behaviors. QTL analyses of head-pokes (HP) and fecal boli (FB) only identified QTL at the suggestive level of significance. Age accounted for ∼15% of the phenotypic variance (sex ∼3%), and there were genotype by age interactions at ∼25% of the Hbact and Hbrear QTL. Quantitative trait loci for Hbrear were relatively stable across the three measurement occasions (those for Hbact somewhat less so), although mean levels of each index declined markedly comparing the first to subsequent trials. Considered as a whole, the polygenic system influencing exploratory behaviors accounts for approximately the same amount of phenotypic variance as age (within the range studied), is stable across substantial periods of time, and acts, for the most part, independently of age and sex.     

Mapping of QTL on chromosome X for fat deposition, muscling and growth traits in a wild boar x Meishan F2 family using a high-density gene map

Quantitative trait loci (QTL) for fat deposition, growth and muscling traits have been previously mapped on the basis of low-density linkage maps in a wild boar × Meishan F₂ family to the chromosome X region flanked by SW2456 and SW1943 . Improved QTL resolution was possible using data for F₂ animals with a marker density of 2.7 cM distance in the SW2456 to SW1943 region, including AR , SERPINA7 and ACSL4 as candidate genes. The resolution of the QTL scan was increased substantially, as evidenced by the higher F -ratio values for all QTL. Maxima of F -ratio values for fat deposition, muscling and growth traits were 28.6, 18.2 and 16.5 respectively, and those QTL positions accounted for 7.9%, 5.0% and 4.5% of the F₂ phenotypic variance (VF₂) respectively. QTL for fatness and growth and for most muscling traits mapped near ACSL4 , with the exception of the QTL for ham traits that mapped proximally, in the vicinity of AR . An analysis performed separately for F₂ male animals showed the predominant QTL affecting fat deposition traits (up to 13.6% VF₂) near AR and two QTL for muscling traits (up to 9.9% VF₂) mapped close to ACSL4 . In the F₂ female animals, QTL affecting muscling (up to 12.1% VF₂) mapped at ACSL4 and SW2456 , and QTL for fat deposition (10% VF₂) and growth (up to 10.5% VF₂) mapped at ACSL4 .     

Mapping quantitative trait loci regulating chicken body composition traits

Genome scans were conducted on an F₂ resource population derived from intercross of the White Plymouth Rock with the Silkies Fowl to detect QTL affecting chicken body composition traits. The population was genotyped with 129 microsatellite markers and phenotyped for 12 body composition traits on 238 F₂ individuals from 15 full-sib families. In total, 21 genome-wide QTL were found to be responsible for 11 traits, including two newly studied traits of proventriculus weight and shank girth. Three QTL were genome-wide significant: at 499 c m on GGA1 (explained 3.6% of phenotypic variance, P  < 0.01) and 51 c m on GGA5 (explained 3.3% of phenotypic variance, P  < 0.05) for the shank & claw weight and 502 c m on GGA1 (explained 1.4% of phenotypic variance, P  < 0.05) for wing weight. The QTL on GGA1 seemed to have pleiotropic effects, also affecting gizzard weight at 490 c m , shank girth at 489 c m and intestine length at 481 c m . It is suggested that further efforts be made to understand the possible pleiotropic effects of the QTL on GGA1 and that on GGA5 for two shank-related traits.     

A major QTL for acute ethanol sensitivity in the alcohol tolerant and non-tolerant selected rat lines

The Alcohol Tolerant and Alcohol Non-Tolerant rats (AT, ANT) were selectively bred for ethanol-induced ataxia as measured on the inclined plane. Here we report on a quantitative trait locus (QTL) study in an F₂ intercross population derived from inbred AT and ANT (IAT, IANT) and a follow-up study of congenics that were bred to examine one of the mapped QTLs. Over 1200 F₂ offspring were tested for inclined plane sensitivity, acute tolerance on the inclined plane, duration of the loss of righting reflex (LORR) and blood ethanol at regain of the righting reflex (BECRR). F₂ rats that were in the upper and lower 20% for inclined plane sensitivity were genotyped with 78 SSLP markers. Significant QTLs for inclined plane sensitivity were mapped on chromosomes 8 and 20; suggestive QTLs were mapped on chromosomes 1, 2 and 3. Highly significant QTLs for LORR duration (LOD = 12.4) and BECRR (LOD = 5.7) were mapped to the same locus on chromosome 1. Breeding and testing of reciprocal congenic lines confirmed the chromosome 1 LORR/BECRR QTL. A series of recombinant congenic sub-lines were bred to fine-map this QTL. Current results have narrowed the QTL to an interval of between 5 and 20 Mb. We expect to be able to narrow the interval to less than 5 Mb with additional genotyping and continued breeding of recombinant sub-congenic lines.     

A non-synonymous mutation in a conserved site of the MTTP gene is strongly associated with protein activity and fatty acid profile in pigs

Despite the economic interest of the fatty acid profile in pigs, no gene has been convincingly associated with this trait so far. Here, the porcine microsomal triglyceride transfer protein ( MTTP ) gene, which plays a crucial role in the assembly of nascent lipoproteins, has been analysed as a positional candidate gene for a QTL affecting the fatty acid composition that was previously identified on chromosome 8 in an Iberian by Landrace F₂ cross. By resequencing a panel of different breeds, a non-synonymous polymorphism in a conserved residue of the lipid transfer domain of MTTP was identified. Association analyses with this polymorphism showed a strong association with the fatty acid composition of porcine fat, much stronger than the QTL effect, in the F₂ cross and in a synthetic Sino-European line. In addition, in vitro activity assays in liver protein extracts have shown that this mutation is also associated with the lipid transfer activity of the MTTP protein ( P  <   0.1). These results suggest that the detected polymorphism is a potential causal factor of the fatty acid composition QTL. There appears to be an interaction between the porcine MTTP genotype and the type of fat source in the pig diet, which would agree with the previous results on the biology of MTTP biology.     

Quantitative trait loci associated with fatness in a broiler–layer cross

An F₂ population established by crossing a broiler male line and a layer line was used to map quantitative trait loci (QTL) affecting abdominal fat weight, abdominal fat percentage and serum cholesterol and triglyceride concentrations. Two genetic models, the line-cross and the half-sib, were applied in the QTL analysis, both using the regression interval method. Three significant QTL and four suggestive QTL were mapped in the line-cross analysis and four significant and four suggestive QTL were mapped in the half-sib analysis. A total of five QTL were mapped for abdominal fat weight, six for abdominal fat percentage and four for triglyceride concentration in both analyses. New QTL associated with serum triglyceride concentration were mapped on GGA5, GGA23 and GG27. QTL mapped between markers LEI0029 and ADL0371 on GGA3 for abdominal fat percentage and abdominal fat weight and a suggestive QTL on GGA12 for abdominal fat percentage showed significant parent-of-origin effects. Some QTL mapped here match QTL regions mapped in previous studies using different populations, suggesting good candidate regions for fine-mapping and candidate gene searches.     

Calcium taste preferences: genetic analysis and genome screen of C57BL/6J x PWK/PhJ hybrid mice

To characterize the genetic basis of voluntary calcium consumption, we tested C57BL/6J mice (B6; with low avidity for calcium), PWK/PhJ mice (PWK; with high avidity for calcium) and their F₁ and F₂ hybrids. All mice received a series of 96-h two-bottle preference tests with a choice between water and the following: 50 m m CaCl₂, 50 m m calcium lactate, 50 m m MgCl₂, 100 m m KCl, 100 m m NH₄Cl, 100 m m NaCl, 5 m m citric acid, 30 μ m quinine hydrochloride and 2 m m saccharin. Most frequency distributions of the parental and F₁ but not F₂ groups were normally distributed, and there were few sex differences. Reciprocal cross analysis showed that B6 × PWK F₁ mice had a non-specific elevation of fluid intake relative to PWK × B6 F₁ mice. In the F₂ mice, trait correlations were clustered among the divalent salts and the monovalent chlorides. A genome screen involving 116 markers showed 30 quantitative trait loci (QTLs), of which six involved consumption of calcium chloride or lactate. The results show pleiotropic controls of calcium and magnesium consumption that are distinct from those controlling consumption of monovalent chlorides or exemplars of the primary taste qualities.     

Two consensus quantitative trait loci clusters controlling anthesis–silking interval, ear setting and grain yield might be related with drought tolerance in maize

Unravelling the molecular basis of drought tolerance will provide novel opportunities for improving crop yield under water-limited conditions. The present study was conducted to identify quantitative trait loci (QTLs) controlling anthesis–silking interval (ASI), ear setting percentage (ESP) and grain yield (GY). The mapping population included 234 F₂ plants derived from the cross X178 (drought tolerant) × B73 (drought susceptible). The corresponding F_2:3 progenies, along with their parents, were evaluated for the above-mentioned traits under both well-watered and water-stressed field conditions in three different trials carried out in central and southern China. Interval mapping and composite interval mapping identified 45 and 65 QTLs for the investigated traits, respectively. Two QTL clusters influencing ASI and ESP on chromosomes 1 (bin 1.03) and 9 (bins 9.03–9.05) were identified in more than two environments, showing sizeable additive effects and contribution to phenotypic variance; these two QTL clusters influenced GY only in one environment. No significant interaction was detected between the two genomic regions. A comparative analysis of these two QTL clusters with the QTLs controlling maize drought tolerance previously described in three mapping populations confirmed and extended their relevance for marker-assisted breeding to improve maize production under water-limited conditions.     

Grey plumage colouration in the duck is genetically determined by the alleles on two different, interacting loci

Based on the observation of a grey phenotype in the F₁ generation from a cross between two white plumage duck varieties, the white Kaiya and the white Liancheng , we hypothesized a possible interaction between two autosomal loci that determine grey plumage. Using the parental and F₁ individuals, seven testing combinations including five different F₁ intercrosses (F₂) and two different backcrosses (BC₁ and BC₂) were designed to test our hypothesis. It was demonstrated by chi-squared analysis that six test matings produced offspring in the expected ratios between the grey and white, with P- values ranging from 0.50 to 0.99. Another mating, where all white offspring were expected, produced 33 white individuals. These results verified that the interaction between two loci produced the grey phenotype. The C locus, which carries the recessive allele ( c ), was previously thought to be the only gene responsible for white plumage in the duck. This is the first report that an allele ( t ), carried by the white Liancheng at a different autosomal locus, also determines white plumage in ducks. Furthermore, the dominant alleles at both loci can interact with each other to produce the grey phenotype, and a new dark phenotype, observed in some F₂ individuals, can be attributed to the dosage effect of the T allele.     

Identification and verification of QTL associated with growth traits in two genetic backgrounds of Barramundi (Lates calcarifer)

Quantitative trait loci (QTL) affecting growth traits have previously been mapped in linkage groups (LG) 2, 3 and 23 of Barramundi ( Lates carcalifer ), but these QTL have not been verified in different genetic backgrounds and environments. Here, we report the identification and verification of QTL for growth traits on LG2, 3, 10 and 23 in F₁ families constructed using brooders from the Singapore Marine Aquaculture Center (MAC) and from wild stocks collected in Thailand (THAI). The previously detected QTL for body weight and length linked to marker Lca371 on LG2 were confirmed in both the MAC and THAI families, whereas other QTL previously mapped to LG3 and 23 were only detected in one of the two families. QTL for body weight and length were identified in the MAC family, but not in the THAI family, in a region where the insulin-like growth factor 2 ( IGF2 ) and tyrosine hydroxylase 1 ( TH1 ) genes are located on LG10. Significant epistatic interactions were identified between markers Lca287 on LG2 and IGF2 on LG10 for growth trait QTL in the MAC family, but not in the THAI family. Effects of the IGF2 , TH1 and parvalbumin 1 candidate genes were family-specific. Our results indicate that some but not all QTL are family-specific in Barramundi.     

Quantitative trait loci for red blood cell traits in swine

Haematological traits are essential diagnostic parameters in veterinary practice but knowledge on the genetic architecture controlling variability of erythroid traits is sparse, especially in swine. To identify QTL for erythroid traits in the pig, haematocrit (HCT), haemoglobin (HB), erythrocyte counts (RBC) and mean corpuscular haemoglobin content (MCHC) were measured in 139 F₂ pigs from a Meishan/Pietrain family, before and after challenge with the protozoan pathogen Sarcocystis miescheriana . The pigs passed through three stages representing acute disease, reconvalescence and chronic disease. Forty-three single QTL controlling erythroid traits were identified on 16 chromosomes. Twelve of the QTL were significant at the genome-wide level while 31 were significant at a chromosome-wide level. Because erythroid traits varied with health and disease status, QTL influencing the erythroid phenotypes showed specific health/disease patterns. Regions on SSC5, 7, 8, 12 and 13 contained QTL for baseline erythroid traits, while the other QTL regions affected distinct stages of the disease model. Single QTL explained 9–17% of the phenotypic variance in the F₂ animals. Related traits were partly under common genetic influence. Our analysis confirms that erythroid trait variation differs between Meishan and Pietrain breeds and that this variation is associated with multiple chromosomal regions.     

Artificial hybridization within Saxifraga pentadactylis (Saxifragaceae)

Saxifraga pentadactylis subsp. almanzorii , an endemic to the subalpine nucleus of Sierra de Gredos (central Spain), differs from its closest relative, subsp. willkommiana , by its less showy petals. An artificial crossing program was carried out in order to assess the degree of reproductive isolation between the subspecies. To facilitate interpretation of the results, the program was extended to 10 other interspecific hybrid combinations within sect. Saxifraga . All the data gathered are congruent with the occurrence of two evolutionary scenarios. Interspecific crossings, rendering moderate to high seed-set (in obtaining the F₁), and vigorous but relatively sterile F₁ offspring, reveal reproductive barriers at the level of the F₁ fertility, probably originated as a byproduct of divergent evolution. In contrast, intraspecific crossings within S. pentadactylis resulted in seed-set values lower than expected (in obtaining the F₁), in a majority of weak non-viable F₁ offspring but also in a few fertile F₁ hybrid specimens which were able to originate F₂ offspring. This second pattern reveals reproductive barriers at the level of the F₁ vitality, probably arisen in a quite abrupt fashion. The lower P/O for subsp. almanzorii as compared to subsp. willkommiana , together with the rest of the evidence suggest that the reproductive barriers between them might be the product of active selection against hybridization achieved by incrementing the levels of autogamy in the former.     

Quantitative trait loci for white blood cell numbers in swine

Differential white blood cell counts are essential diagnostic parameters in veterinary practice but knowledge on the genetic architecture controlling variability of leucocyte numbers and relationships is sparse, especially in swine. Total leucocyte numbers (Leu) and the differential leucocyte counts, i.e. the fractions of lymphocytes (Lym), polymorphonuclear leucocytes [neutrophils (Neu), eosinophils (Eos) and basophils (Bas)] and monocytes (Mon) were measured in 139 F₂ pigs from a Meishan/Pietrain family, before and after challenge with the protozoan pathogen Sarcocystis miescheriana for genome-wide quantitative trait loci (QTL) analysis. After infection, the pigs passed through three stages representing acute disease, reconvalescence and chronic disease. Nine genome-wide significant and 29 putative, single QTL controlling leucocyte traits were identified on 15 chromosomes. Because leucocyte traits varied with health and disease status, QTL influencing the leucocyte phenotypes showed specific health/disease patterns. Regions on SSC1, 8 and 12 contained QTL for baseline leucocyte traits. Other QTL regions reached control on leucocyte traits only at distinct stages of the disease model. Two-thirds of the QTL have not been described before. Single QTL explained up to 19% of the phenotypic variance in the F₂ animals. Related traits were partly under common genetic influence. Our analysis confirms that leucocyte trait variation is associated with multiple chromosomal regions.     

Genetic analysis of seed size, yield and days to flowering in a chickpea recombinant inbred line population derived from a Kabuli × Desi cross

Quantitative traits, seed size, yield and days to flowering were studied in a chickpea intraspecific recombinant inbred line (RIL) population (F_6:7) derived from a Kabuli × Desi cross. The population was evaluated in two locations over 2 years. Days to flowering was also evaluated in the greenhouse under short-day conditions. Seed size was the most heritable trait (0.90), followed by days to flowering (0.36) and yield (0.14). Negative and significant correlation was found between yield and seed size in the second year where environmental homogeneity was tested by analysing the controls included in each assay. During the first year, the environment was not considered homogeneous for yield in either location. Quantitative trait loci (QTLs) for the three characters were detected in linkage group (LG) 4. In relation to seed size, two QTLs were located in LG4 (QTL_SW1) and LG8 (QTL_SW2). QTL_SW1 accounted 20.3% of the total phenotypic variation and QTL_SW2 explained 10.1%. A QTL for yield (QTL_YD) was located in LG4 explaining around 13% of variation. QTL_YD might be pleiotropic with QTL_SW1. For days to flowering, a QTL (QTL_DF1) was located in LG4 for all environments analysed explaining around 20% of variation. QTL_DF1 was closely linked to QTL_SW1 and QTL_YD in LG4.     

Heritabilities and quantitative trait loci for blood gases and blood pH in swine

Maintaining pH and blood gases in a narrow range is essential to sustain normal biochemical reactions. Decreased oxygenation, poor tissue perfusion, disturbance to CO₂ expiration, and shortage of HCO₃⁻ can lead to metabolic acidosis. This is a common situation in swine, and originates from a broad range of medical conditions. pH and blood gases appear to be under genetic control, and populations with physiological traits closer to the pathological thresholds may be more susceptible to developing pathological conditions. However, little is known about the genetic basis of such traits. We have therefore estimated phenotypic and genetic variability and identified quantitative trait loci (QTL) for pH and blood gases in blood samples from 139 F₂ pigs from the Meishan/Pietrain family. Samples were taken before and after challenge with Sarcocystis miescheriana , a protozoan parasite of muscle. Twenty-seven QTL influencing pH and blood gases were identified on nine chromosomes. Five of the QTL were significant on a genome-wide level; 22 QTL were significant on a chromosome-wide level. QTL for pH-associated traits have been mapped to SSC3, 18 and X. QTL associated with CO₂ have been detected on SSC6, 7, 8 and 9, and QTL associated with O₂ on SSC2 and SSC8. QTL showed specific health/disease patterns that were related to the physiological state of the pigs from day 0, to acute disease (day 14), convalescence (day 28) and chronic disease (day 42). The results demonstrate that pH and blood gases are influenced by multiple chromosomal areas, each with relatively small effects.     

Quantitative trait loci affecting stomatal density and growth in a Quercus robur progeny: implications for the adaptation to changing environments

Stomatal traits are important to cope with changes in levels of atmospheric carbon dioxide (CO₂) and with changing availability of water. Thus, they are expected to be involved in the reactions of plants to climate change. They are known to show a plastic physiological response to environmental factors such as elevated CO₂ concentrations, but they are also under genetic control and should undergo evolutionary change if selection differs among environments. Stomatal development is regulated by several environmental and genetic signals suggesting a polygenic inheritance. In the present study, F₁ progeny derived from a cross between Quercus robur and Q. robur subsp. slavonica were used to map QTLs (quantitative trait loci) for stomatal densities and growth parameters under nonwater stress conditions in 2 and 3 consecutive years, respectively. The positions of QTLs for stomatal density and growth coincided on six linkage groups. The QTL allele associated with the higher stomatal density was generally associated with taller plants and size increment indicating pleiotropic gene effects or close linkage. The phenotypic effects of the individual QTLs were mostly moderate in terms of phenotypic variance explained. However, a considerable amount of the genetically determined variation was explained by QTLs for stomatal density (from 63.6% to 94.4%). Especially, the QTL on linkage group 11 had a strong and highly significant effect on stomatal densities and growth parameters in all years suggesting a major QTL on this linkage group. The importance to analyse the genetic variation controlling complex adaptive traits in keystone species as oaks is discussed with regard to a better understanding of the reactions of ecosystems to global change.