Quantitative genetic analysis of seed vigour and pre-emergence seedling growth traits in Brassica oleracea

The ability of seeds to germinate and establish seedlings in a predictable manner under a range of conditions has a direct contribution to the economic success of commercial crops, and should therefore be considered in crop improvement. We measured traits associated with seed vigour and pre-emergence seedling growth in a segregating population of 105 doubled haploid Brassica oleracea lines. The germination traits measured were: mean germination times for unstressed germination; germination under water stress or germination after a heat treatment; and conductivity of seed leachate. The seedling growth traits measured were: seed weight; seedling growth rate; and seedling size at the end of the exponential growth phase. There were some correlations, notably among germination traits, and between seed weight and pre-emergence seedling growth. Heritability of the various traits was typically in the 10–15% range, with heritability of conductivity and mean germination time under water stress 25 and 24% respectively. Collectively the results indicate that germination and pre-emergence seedling growth are under separate genetic control. Quantitative trait loci analyses were carried out on all measurements and revealed significant loci on linkage groups O1, O3, O6, O7 and O9. We suggest that genes at these loci are important in determining predictable seed germination and seedling establishment in practice.     

Identification and fine mapping of quantitative trait loci for seed vigor in germination and seedling establishment in rice

Seed vigor is an index of seed quality that is used to describe the rapid and uniform germination and the establishment of strong seedlings in any environmental conditions.Strong seed vigor in low-temperature germination conditions is particularly important in direct-sowing rice production systems. However, seed vigor has not been selected as an important breeding trait in traditional breeding programs due to its quantitative inherence. In this study, we identified and mapped eight quantitative trait loci(QTLs) for seed vigor by using a recombinant inbred population from a cross between rice(Oryza sativa L. ssp. indica) cultivars ZS97 and MH63.Conditional QTL analysis identified qSV-1, qSV-5b, qSV-6a, qSV-6b, and qSV-11 influenced seedling establishment and that qSV-5a, qSV-5c, and qSV-8 influenced only germination. Of these,qSV-1, qSV-5b, qSV-6a, qSV-6b, and qSV-8 were low-temperature-specific QTLs. Two major-effective QTLs, qSV-1, and qSV-5c were narrowed down to 1.13-Mbp and 400-kbp genomic regions, respectively. The results provide tightly linked DNA markers for the marker-assistant pyramiding of multiple positive alleles for increased seed vigor in both normal and low-temperature germination environments.     

Quantitative trait loci analysis of osteochondrosis traits in the elbow joint of pigs

Osteochondrosis is a growth disorder in the cartilage of young animals and is characterised by lesions found in the cartilage and bone. This study identified quantitative trait loci (QTLs) associated with six osteochondrosis lesion traits in the elbow joint of finishing pigs. The traits were: thickening of the cartilage, lesion in the subchondral bone, irregular cartilage surface, fissure under the cartilage, an irregular sagittal central groove and depression of the proximal edge of the radius. The study comprised 7172 finishing pigs from crossing 12 Duroc boars with 600 crossbred Landrace × Large White sows and included 462 single nucleotide polymorphism markers. The results showed 18 QTLs exceeding the 5% genome-wide threshold. The QTLs associated with lesions in the medial part of the condylus humeri (assumed to be the four main osteochondrosis traits) were, in most cases, at common locations, whereas the QTLs associated with depression of the proximal edge of the radius in general were on the same chromosomes but at separate locations. The detected QTLs explain a large part of the genetic variation, which is promising for incorporating osteochondrosis into a breeding programme using marker-assisted selection.     

Genetic variation in pea (Pisum sativum L.) demonstrates the importance of root but not shoot C/N ratios in the control of plant morphology and reveals a unique relationship between shoot length and nodulation intensity

Nodule numbers are regulated through systemic auto‐regulatory signals produced by shoots and roots. The relative effects of shoot and root genotype on nodule numbers together with relationships to organ biomass, carbon (C) and nitrogen (N) status, and related parameters were measured in pea (Pisum sativum) exploiting natural genetic variation in maturity and apparent nodulation intensity. Reciprocal grafting experiments between the early (Athos), intermediate (Phönix) and late (S00182) maturity phenotypes were performed and Pearson's correlation coefficients for the parameters were calculated. No significant correlations were found between shoot C/N ratios and plant morphology parameters, but the root C/N ratio showed a strong correlation with root fresh and dry weights as well as with shoot fresh weight with less significant interactions with leaf number. Hence, the root C/N ratio rather than shoot C/N had a predominant influence on plant morphology when pea plants are grown under conditions of symbiotic nitrogen supply. The only phenotypic characteristic that showed a statistically significant correlation with nodulation intensity was shoot length, which accounted for 68.5% of the variation. A strong linear relationship was demonstrated between shoot length and nodule numbers. Hence, pea nodule numbers are controlled by factors related to shoot extension, but not by shoot or root biomass accumulation, total C or total N. The relationship between shoot length and nodule numbers persisted under field conditions. These results suggest that stem height could be used as a breeding marker for the selection of pea cultivars with high nodule numbers and high seed N contents.     

Quantitative trait loci analysis of egg and meat production traits in a red junglefowlxWhite Leghorn cross

Egg and production traits are of considerable economic importance in chickens. Using a White Leghorn x red junglefowl F(2) intercross, standard production measures of liver weight and colour, egg size, eggshell thickness, egg taste and meat quality were taken. A total of 160 markers covering 29 autosomes and the Z chromosome were genotyped on 175-243 individuals, depending on the trait under consideration. A total of nine significant quantitative trait loci (QTL) and three suggestive QTL were found on chicken chromosomes 1, 2, 4, 5, 7, 8, 10, 12, E47W24 and E22C19W28.     

Relationship between seed and clonal growth in the reproduction of Carex rugulosa Kük. in riverside meadows

Carex rugulosa Kük. develops riverside vegetation in brackish marshes along the lower parts of rivers. Because the rhizomatous ramets grow densely (590–950/m²) in its developed population, it is expected that seedlings cannot get enough light to grow if seeds germinate in crowded ramets. We studied the reproductive contribution of seed in a marshy meadow of the Ohashi River, Japan. The number of seeds produced was 6900–14 200/m² in 2002. The number of buried seeds in the following germination season differed among sites from 1190 to 2690/m². No seedlings were observed at plots where the ramets from rhizomes grew densely. In contrast, seedlings appeared in plots where all rhizomatous ramets were artificially cut. The number of seedlings corresponded to 17.5–39.5% of that of buried seeds. All these seedlings were submerged and died when it rained heavily. In the genotype analysis using allozyme detection, one of the phosphoglucoisomerase loci ( Pgi-2 ) indicated a pair of alleles. Among eight plots (each plot was 50 or 60-cm square), four showed an excess of heterozygotes and two showed homozygote domination in the Pgi-2 genotype. These results suggest that: (i) seed germination is suppressed in crowded ramets; (ii) seedling survival is severely reduced by inundation; and (iii) the population is usually maintained by clonal growth. As germination is induced in open areas, it is hypothesized that the main role of seed is recovery after vegetation decline caused by environmental stresses or colonization to other areas without dense vegetation.     

Variation at enzyme coding loci and correlates of fitness in rainbow trout: a cohort analysis

An association between heterozygosity at six to nine enzyme coding loci and correlates of fitness (survival, age at first maturation) was tested in two cohorts of rainbow trout Oncorhynchus mykiss reared in the laboratory. A subsample offish from the first cohort was reared together for 3 years. There, fish sampled as embryos, juveniles and adults did not differ significantly in multilocus heterozygosity (MLH, numbers of heterozygous loci per fish). However, fish that died during a period of high natural mortality had significantly greater MLH than those sampled before as hatched embryos and later as adults. The number of homozygotes and heterozygotes at three loci differed significantly among different aged fish but in different directions. Allele counts at two of these loci also differed among samples. In a second cohort, the heterozygosity of fish that died during the period of high natural mortality was compared with that of healthy fish collected at the same time; no significant differences in MLH or allele frequencies were detected. Taken together, the lower MLH of the natural mortalities as well as single locus effects observed in the first cohort might be explained by the differential survival of fish with particular genotypes leading to changes in heterozygosity of the entire cohort over time rather than heterozygosity per se . Age of first maturation and heterozygosity (MLH and single locus) were not associated in males but were marginally so in females. Time of ovulation within the spawning season was not associated with the MLH of females.     

MtZR1, a PRAF protein,is involved in the development of roots and symbiotic root nodules in Medicago truncatula

PRAF proteins are present in all plants, but their functions remain unclear. We investigated the role of one member of the PRAF family, MtZR1, on the development of roots and nitrogen‐fixing nodules in Medicago truncatula. We found that MtZR1 was expressed in all M. truncatula organs. Spatiotemporal analysis showed that MtZR1 expression in M. truncatula roots was mostly limited to the root meristem and the vascular bundles of mature nodules. MtZR1 expression in root nodules was down‐regulated in response to various abiotic stresses known to affect nitrogen fixation efficiency. The down‐regulation of MtZR1 expression by RNA interference in transgenic roots decreased root growth and impaired nodule development and function. MtZR1 overexpression resulted in longer roots and significant changes to nodule development. Our data thus indicate that MtZR1 is involved in the development of roots and nodules. To our knowledge, this work provides the first in vivo experimental evidence of a biological role for a typical PRAF protein in plants.     

Quantitative trait loci analysis of seed‐specialized metabolites reveals seed‐specific flavonols and differential regulation of glycoalkaloid content in tomato

Given the potential health benefits (and adverse effects), of polyphenolic and steroidal glycoalkaloids in the diet there is a growing interest in fully elucidating the genetic control of their levels in foodstuffs. Here we carried out profiling of the specialized metabolites in the seeds of the Solanum pennellii introgression lines identifying 338 putative metabolite quantitative trait loci (mQTL) for flavonoids, steroidal glycoalkaloids and further specialized metabolites. Two putative mQTL for flavonols and one for steroidal glycoalkaloids were cross‐validated by evaluation of the metabolite content of recombinants harboring smaller introgression in the corresponding QTL interval or by analysis of lines from an independently derived backcross inbred line population. The steroidal glycoalkaloid mQTL was localized to a chromosomal region spanning 14 genes, including a previously defined steroidal glycoalkaloid gene cluster. The flavonoid mQTL was further validated via the use of transient and stable overexpression of the Solyc12g098600 and Solyc12g096870 genes, which encode seed‐specific uridine 5′‐diphosphate‐glycosyltransferases. The results are discussed in the context of our understanding of the accumulation of polyphenols and steroidal glycoalkaloids, and how this knowledge may be incorporated into breeding strategies aimed at improving nutritional aspects of plants as well as in fortifying them against abiotic stress.     

Growth and reproductive responses to elevated CO2 in wild cereals of the northern Negev of Israel

How might wild relatives of modern cereals have responded to past, and how might they respond to future, atmospheric CO₂ enrichment under competitive situations in a dry, low‐nutrient environment? In order to test this, Aegilops and Hordeum species, common in semiarid annual grasslands of the Middle East, were grown in nine model ecosystems (400 kg each) with a natural matrix of highly diverse Negev vegetation established on native soil shipped to Basel, Switzerland. In a simulated, seasonally variable climate of the northern Negev, communities experienced a full life‐cycle in 280 (preindustrial), 440 (immediate future) and 600 ppm of CO₂ (end of the next century). Neither Aegilops (A. kotschyi and A. peregrina), nor Hordeum spontaneum showed a significant biomass response to CO₂ concentrations exceeding 280 ppm The reproductive output remained unaffected or even declined (A. peregrina) under elevated CO₂. Non‐structural carbohydrates in leaf tissues increased and N concentration decreased with increasing CO₂ concentration. N concentration, germination success and seedling development of newly formed grains were either unchanged or reduced in response to high CO₂ treatment of parent plants. In a separate fertilizer × CO₂ trial with A. kotschyi nested in smaller model communities, we found no effect of P addition, but a 2–3‐fold biomass increase by NPK addition compared to the unfertilized control. A significant stimulation of biomass by CO₂ enrichment (+ 44% between 280 and 600 ppm) was obtained only in the NPK treatment. These data suggest that increased CO₂ concentration had little direct effect on growth and reproduction in these ‘wild cereals’ in the recent past, and the same seems to hold for their future, except if N‐rich fertilizer is added.     

Quantitative trait loci analysis for the differences in susceptibility to atherosclerosis and diabetes between inbred mouse strains C57BL/6J and C57BLKS/J.

Mice from the inbred strain C57BLKS/J (BKS) exhibit increased susceptibility to both diabetes and atherosclerosis compared to C57BL/6J (B6) mice. To determine whether the differences in diabetes and atherosclerosis are related, we carried out a cross between B6-db/db and BKS. We selected 99 female F2-db/db progeny, tested the progeny for plasma lipids, plasma glucose, and fatty-streak lesions, and used quantitative trait loci (QTL) analysis to identify the chromosomal regions associated with these phenotypes. No major QTL were found for total cholesterol, VLDL-cholesterol, or triglycerides. Two suggestive QTL were found for HDL-cholesterol (LOD scores of 2. 7 and 2.8), and two suggestive loci were found for plasma glucose (LOD scores of 2.3 and 2.0). Lesion size was not correlated with plasma lipid levels or glucose. Lesion size was determined by a locus at D12Mit49 with a LOD score of 2.5 and a significant likelihood ratio statistic. The gene for apolipoprotein apoB lies within the region, but apoB levels were similar in strains B6 and BKS. The QTL on Chr 12 was confirmed by constructing a congenic strain with BKS alleles in the QTL region on a B6 genetic background. We conclude that susceptibilities to diabetes and atherosclerosis are not conferred by the same genes in these strains and that a major gene on Chr 12, which we name Ath6, determines the difference in atherosclerosis susceptibility.     

Costs of resistance in the Drosophila-macrocheles system: a negative genetic correlation between ectoparasite resistance and reproduction

Genetic variation for parasite resistance occurs in most host populations. Costs of resistance, manifested as reduced fitness of resistant genotypes in the absence of parasitism, can be an important factor contributing to the maintenance of this variation. One powerful tool for detecting costs of resistance is the study of correlated responses to artificial selection. Provided that experimental lines are recently derived from large outbreeding populations, and that inbreeding is minimized during the experiment, correlated responses to selection are expected to be strong indicators of pleiotropy. We artificially selected for elevated behavioral resistance against an ectoparasitic mite (Macrocheles subbadius) in replicate populations of the fly Drosophila nigrospiracula. Resistance was modeled as a threshold trait, and the realized heritability of resistance was estimated to be 12.3% (1.4% SE) across three replicate lines recently derived from nature. We contrasted the longevity and fecundity of resistant and control (unselected) flies under a variable thermal environment. We report that reduced fecundity is a correlated response to artificial selection for increased resistance, and that the strength of this effect increases from 25 degrees to 29 degrees C. In contrast, longevity differences were not detected between resistant and control lines at either temperature. These findings are robust as they were confirmed with an independent set of experimental lines. Thus, our results identify a negative genetic correlation between ectoparasite resistance and an important life-history trait. That a correlated response was only detected for fecundity, and not longevity, suggests that the genetic correlation is attributable to pleiotropic effects with narrower effects than reallocation of a general resource pool within the organism, although other interpretations are discussed. Combined with fluctuating parasite-mediated selection and temperature, the presence of this trade-off may contribute to the maintenance of genetic variation for resistance in natural populations.     

Quantitative trait loci for urinary albumin in crosses between C57BL/6J and A/J inbred mice in the presence and absence of Apoe

We investigated the effect of apolipoprotein E (Apoe) on albuminuria in the males of two independent F2 intercrosses between C57BL/6J and A/J mice, using wild-type inbred strains in the first cross and B6-Apoe(-/-) animals in the second cross. In the first cross, we identified three quantitative trait loci (QTL): chromosome (Chr) 2 [LOD 3.5, peak at 70 cM, confidence interval (C.I.) 28-88 cM]; Chr 9 (LOD 2.0, peak 5 cM, C.I. 5-25 cM); and Chr 19 (LOD 1.9, peak 49 cM, C.I. 23-54 cM). The Chr 2 and Chr 19 QTL were concordant with previously found QTL for renal damage in rat and human. The Chr 9 QTL was concordant with a locus found in rat. The second cross, testing only Apoe(-/-) progeny, did not identify any of these loci, but detected two other loci on Chr 4 (LOD 3.2, peak 54 cM, C.I. 29-73 cM) and Chr 6 (LOD 2.6, peak 33 cM, C.I. 11-61 cM), one of which was concordant with a QTL found in rat. The dependence of QTL detection on the presence of Apoe and the concordance of these QTL with rat and human kidney disease QTL suggest that Apoe plays a role in renal damage.     

亚热带中山常绿阔叶林木本植物幼苗数量动态及其与生境的相关性

以百山祖自然保护区5 hm2永久样地150个幼苗监测站木本植物幼苗为研究对象,2008—2011年定期调查样方中幼苗的种类、数量、萌发、死亡等,探究亚热带中山常绿阔叶林幼苗种类组成、数量动态及其与生境的相关性。结果表明:1)百山祖样地在2008年至2011年出现的幼苗属于26科,40属,共53个物种,不同物种萌发时段有异;2)2009年样地幼苗存活比率为7.7%,2010年为-20.8%,2011年则是-0.3%,幼苗存活比率不高,种类和数量呈减少趋势;3)存活幼苗中有明显的优势物种,分别为光亮山矾(Symplocos lucida)、尖连蕊茶(Camellia cuspidata)、浙闽新木姜子(Neolitsea aurata var.undulatula)、尖叶菝葜(Smilax arisanensis)和短尾柯(Lithocarpus brevicaudatus),5个物种之和占幼苗总数比例50%;4)种子的萌发与生境有极显著的相关性,且与生境因子中水分关联最大;5)存活幼苗数与样站坡位、水分、落叶层厚度呈现显著相关性,水和光照是影响幼苗存活的主要因素。     

Genetic structure of the date palm (Phoenix dactylifera) in the Old World reveals a strong differentiation between eastern and western populations

Background and Aims Rock pools are small, geologically stable freshwater ecosystems that are both hydrologically and biologically isolated. They harbour high levels of plant endemism and experience environmental unpredictability driven by the presence of water over variable temporal scales. This study examined the hypothesis that the sediment seed bank in monsoon tropical freshwater rock pools would persist through one or more periods of desiccation, with seed dormancy regulating germination timing in response to rock pool inundation and drying events.Methods Seeds were collected from seven dominant rock pool species, and germination biology and seed dormancy were assessed under laboratory conditions in response to light, temperature and germination stimulators (gibberellic acid, karrikinolide and ethylene). Field surveys of seedling emergence from freshwater rock pools in the Kimberley region of Western Australia were undertaken, and sediment samples were collected from 41 vegetated rock pools. Seedling emergence and seed bank persistence in response to multiple wetting and drying cycles were determined.Key Results The sediment seed bank of individual rock pools was large (13 824 ± 307 to 218 320 ± 42 412 seeds m⁻² for the five species investigated) and spatially variable. Seedling density for these same species in the field ranged from 13 696 to 87 232 seedlings m⁻². Seeds of rock pool taxa were physiologically dormant, with germination promoted by after-ripening and exposure to ethylene or karrikinolide. Patterns of seedling emergence varied between species and were finely tuned to seasonal temperature and moisture conditions, with the proportions of emergent seedlings differing between species through multiple inundation events. A viable seed bank persisted after ten consecutive laboratory inundation events, and seeds retained viability in dry sediments for at least 3 years.Conclusions The persistent seed bank in freshwater rock pools is likely to provide resilience to plant communities against environmental stochasticity. Since rock pool communities are often comprised of highly specialized endemic and range-restricted species, sediment seed banks may represent significant drivers of species persistence and diversification in these ecosystems.     

Identification of quantitative trait loci and a candidate locus for freezing tolerance in controlled and outdoor environments in the overwintering crucifer Boechera stricta

Development of chilling and freezing tolerance is complex and can be affected by photoperiod, temperature and photosynthetic performance; however, there has been limited research on the interaction of these three factors. We evaluated 108 recombinant inbred lines of Boechera stricta, derived from a cross between lines originating from Montana and Colorado, under controlled long day (LD), short‐day (SD) and in an outdoor environment (OE). We measured maximum quantum yield of photosystem II, lethal temperature for 50% survival and electrolyte leakage of leaves. Our results revealed significant variation for chilling and freezing tolerance and photosynthetic performance in different environments. Using both single‐ and multi‐trait analyses, three main‐effect quantitative trait loci (QTL) were identified. QTL on linkage group (LG)3 were SD specific, whereas QTL on LG4 were found under both LD and SD. Under all conditions, QTL on LG7 were identified, but were particularly predictive for the outdoor experiment. The co‐localization of photosynthetic performance and freezing tolerance effects supports these traits being co‐regulated. Finally, the major QTL on LG7 is syntenic to the Arabidopsis C‐repeat binding factor locus, known regulators of chilling and freezing responses in Arabidopsis thaliana and other species.     

A meta‐analysis reveals a positive correlation between genetic diversity metrics and environmental status in the long‐lived seagrass Posidonia oceanica

The seagrass Posidonia oceanica is a key engineering species structuring coastal marine systems throughout much of the Mediterranean basin. Its decline is of concern, leading to the search for short‐ and long‐term indicators of seagrass health. Using ArcGIS maps from a recent, high‐resolution (1–4 km) modelling study of 18 disturbance factors affecting coastal marine systems across the Mediterranean (Micheli et al. 2013, http://globalmarine.nceas.ucsb.edu/mediterranean/ ), we tested for correlations with genetic diversity metrics (allelic diversity, genotypic/clonal diversity and heterozygosity) in a meta‐analysis of 56 meadows. Contrary to initial predictions, weak but significantly positive correlations were found for commercial shipping, organic pollution (pesticides) and cumulative impact. This counterintuitive finding suggests greater resistance and resilience of individuals with higher genetic and genotypic diversity under disturbance (at least for a time) and/or increased sexual reproduction under an intermediate disturbance model. We interpret the absence of low and medium levels of genetic variation at impacted locations as probable local extinctions of individuals that already exceeded their resistance capacity. Alternatively, high diversity at high‐impact sites is likely a temporal artefact, reflecting the mismatch with pre‐environmental impact conditions, especially because flowering and sexual recruitment are seldom observed. While genetic diversity metrics are a valuable tool for restoration and mitigation, caution must be exercised in the interpretation of correlative patterns as found in this study, because the exceptional longevity of individuals creates a temporal mismatch that may falsely suggest good meadow health status, while gradual deterioration of allelic diversity might go unnoticed.     

Study of the relationship between pre-harvest sprouting and grain color by quantitative trait loci analysis in a whitexred grain bread-wheat cross

In many wheat (Triticum aestivum L.) growing areas, pre-harvest sprouting (PHS) may cause important damage, and in particular, it has deleterious effects on bread-making quality. The relationship between PHS and grain color is well known and could be due either to the pleiotropic effect of genes controlling red-testa pigmentation (R) or to linkage between these genes and other genes affecting PHS. In the present work, we have studied a population of 194 recombinant inbred lines from the cross between two cultivars, ’Renan’ and ’Récital’, in order to detect QTLs for both PHS resistance and grain color. The variety ’Renan’ has red kernels and is resistant to PHS, while ’Récital’ has white grain and is highly susceptible to PHS. A molecular-marker linkage map of this cross was constructed using SSRs, RFLPs and AFLPs. The population was evaluated over 2 years at Clermont-Ferrand (France). PHS was evaluated on mature spikes under controlled conditions and red-grain color was measured using a chromameter. Over the 2 years, we detected four QTLs for PHS, all of them being co-localized with QTLs for grain color. Three of them were located on the long arm of chromosomes 3 A, 3B and 3D, close to the loci where the genes R and taVp1 were previously mapped. For these three QTLs, the resistance to PHS is due to the allele of the variety ’Renan’. Another co-located QTL for PHS and grain color was detected on the short arm of chromosome 5 A. The resistance for PHS for this QTL is due to the allele of ’Récital’. Received: 13 December 2000 / Accepted: 24 April 2001     

Deadly combination of genes and drought: increased mortality of herbivore-resistant trees in a foundation species

Current climate models predict a shift to warmer, drier conditions in the southwestern US. While major shifts in plant distribution are expected to follow these climate changes, interactions among species and intraspecific genetic variation rarely have been incorporated into models of future plant distributions. We examined the drought‐related mortality of pinyon pine (Pinus edulis) in northern Arizona focusing on trees that showed genetically‐based resistance or susceptibility to a nonlethal herbivore, the shoot‐boring moth, Dioryctria albovittella. Because moth resistant trees have outperformed susceptible trees during 20 years of study, and herbivory has been shown to increase drought related mortality, we expected higher mortality rates in susceptible trees. However, our field observations and greenhouse experiments showed several unexpected patterns relevant to understanding the consequences of climate change: (1) The mortality of adult P. edulis resistant to the moth was three times higher than the mortality of trees susceptible to the moth. (2) Over a few years, differential mortality caused a shift in stand structure from resistant dominated to equality (3 : 1 resistant : susceptible to 1 : 1). (3) Adult moth resistant trees suffered significantly greater water stress than adult moth susceptible trees, suggesting that variation among the two groups in drought tolerance may be a mechanism for differential mortality. (4) When grown under drought conditions in the greenhouse, seedlings from resistant mothers died sooner than seedlings from susceptible mothers. These data support the hypothesis that drought can act as an agent of balancing selection and that drought resistance is a heritable trait. Taken together, our findings suggest that genetic variation in a population can be an important factor in determining its response to future climate change, and argue for the inclusion of genetics into models developed to understand the consequences of climate change.