The effect of drought stress on heterozygosity-fitness correlations in pedunculate oak (Quercus robur)

Antioxidative responses of three oak species under ozone and water stress conditions

Plants are frequently exposed to adverse environmental conditions such as drought and ozone (O₃). Under these conditions, plants can survive due to their ability to adjust their metabolism. The aim of the present study was to compare the detoxification mechanisms of three oak species showing different O₃ sensitivity and water use strategy. Two-year-old seedlings of Quercus ilex, Q. pubescens and Q. robur were grown under the combination of three levels of O₃ (1.0, 1.2 and 1.4 times the ambient O₃ concentration) and three levels of water availability (on average 100, 80 and 42% of field capacity i.e. well-watered, moderate drought and severe drought, respectively) in an O₃ Free Air Controlled Exposure facility. Ozone and drought induced the accumulation of reactive oxygen species (ROS) and this phenomenon was species-specific. Sometimes, ROS accumulation was not associated with membrane injury suggesting that several antioxidative defence mechanisms inhibited or alleviated the oxidative damage. Both O₃ and drought increased total carotenoids that were able to prevent the peroxidation action by free radicals in Q. ilex, as confirmed by unchanged malondialdehyde by-product values. The concomitant decrease of total flavonoids may be related to the consumption of these compounds by the cell to inhibit the accumulation of hydrogen peroxide. Unchanged total phenols confirmed that Q. ilex has a superior ability to counteract oxidative conditions. Similar responses were found in Q. pubescens, although the negative impact of both factors was less efficiently faced than in the sympatric Q. ilex. In Q. robur, high O₃ concentrations and severe drought induced a partial rearrangement of the phenylpropanoid pathways. These antioxidative mechanisms were not able to protect the cell structure (as confirmed by ROS accumulation) suggesting that Q. robur showed a lower degree of tolerance than the other two species.

Field Populations of Wild Apis cerana Honey Bees Exhibit Increased Genetic Diversity Under Pesticide Stress Along an Agricultural Intensification Gradient in Eastern India

Pesticides have been reported to be one of the major drivers in the global pollinator losses. The large-scale decline in honey bees, an important pollinator group, has resulted in comprehensive studies on honey bee colonies. Lack of information on native wild pollinators has paved the way for this study, which highlights the underlying evolutionary changes occurring in the wild honey bee populations exposed to pesticides along an agricultural intensification landscape. The study reports an increased genetic diversity in native Apis cerana Fabricius (Hymenoptera: Apidae) populations continually exposed to pesticide stress. An increased heterozygosity, evidenced by a higher electrophoretic banding pattern, was observed in the pesticide-exposed populations for two isozymes involved with xenobiotic metabolism-esterase and glucose-6-phosphate dehydrogenase. Differential banding patterns also revealed a higher percentage of polymorphic loci, number of polymorphic bands, Nei's genetic distance, etc. observed in these populations in the Randomly Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR) experiments using three random decamer primers. Higher heterozygosity, being indicative of a more resistant population, implies population survival within the threshold pesticide stress. This study reports such changes for the first time in native wild Indian honey bee populations exposed to pesticides and has far-reaching implications on the population adaptability under pesticide stress.

Genetic variation, phenotypic stability, and repeatability of drought response in European larch throughout 50 years in a common garden experiment

Assessing intra-specific variation in drought stress response is required to mitigate the consequences of climate change on forest ecosystems. Previous studies suggest that European larch (Larix decidua Mill.), an important European conifer in mountainous and alpine forests, is highly vulnerable to drought. In light of this, we estimated the genetic variation in drought sensitivity and its degree of genetic determination in a 50-year-old common garden experiment in the drought-prone northeastern Austria. Tree ring data from larch provenances originating from across the species' natural range were used to estimate the drought reaction in four consecutive drought events (1977, 1981, 1990–1994, and 2003) with extremely low standardized precipitation- and evapotranspiration-index values that affected growth in all provenances. We found significant differences among provenances across the four drought periods for the trees’ capacity to withstand drought (resistance) and for their capacity to reach pre-drought growth levels after drought (resilience). Provenances from the species' northern distribution limit in the Polish lowlands were found to be more drought resistant and showed higher stability across all drought periods than provenances from mountainous habitats at the southern fringe. The degree of genetic determination, as estimated by the repeatability, ranged up to 0.39, but significantly differed among provenances, indicating varying degrees of natural selection at the provenance origin. Generally, the relationship between the provenances’ source climate and drought behavior was weak, suggesting that the contrasting patterns of drought response are a result of both genetic divergence out of different refugial lineages and local adaptation to summer or winter drought conditions. Our analysis suggests that European larch posseses high genetic variation among and within provenances that can be used for assisted migration and breeding programs.

Genomic heterozygosity and hybrid breakdown in cotton (Gossypium): different traits, different effects

Background

Hybrid breakdown has been well documented in various species. Relationships between genomic heterozygosity and traits-fitness have been extensively explored especially in the natural populations. But correlations between genomic heterozygosity and vegetative and reproductive traits in cotton interspecific populations have not been studied. In the current study, two reciprocal F₂ populations were developed using Gossypium hirsutum cv. Emian 22 and G. barbadense acc. 3–79 as parents to study hybrid breakdown in cotton. A total of 125 simple sequence repeat (SSR) markers were used to genotype the two F₂ interspecific populations.

Results

To guarantee mutual independence among the genotyped markers, the 125 SSR markers were checked by the linkage disequilibrium analysis. To our knowledge, this is a novel approach to evaluate the individual genomic heterozygosity. After marker checking, 83 common loci were used to assess the extent of genomic heterozygosity. Hybrid breakdown was found extensively in the two interspecific F₂ populations particularly on the reproductive traits because of the infertility and the bare seeds. And then, the relationships between the genomic heterozygosity and the vegetative reproductive traits were investigated. The only relationships between hybrid breakdown and heterozygosity were observed in the (Emian22 × 3–79) F₂ population for seed index (SI) and boll number per plant (BN). The maternal cytoplasmic environment may have a significant effect on genomic heterozygosity and on correlations between heterozygosity and reproductive traits.

Conclusions

A novel approach was used to evaluate genomic heterozygosity in cotton; and hybrid breakdown was observed in reproductive traits in cotton. These findings may offer new insight into hybrid breakdown in allotetraploid cotton interspecific hybrids, and may be useful for the development of interspecific hybrids for cotton genetic improvement.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0366-5) contains supplementary material, which is available to authorized users.

Repeated Summer Drought and Re-watering during the First Growing Year of Oak (Quercus petraea) Delay Autumn Senescence and Bud Burst in the Following Spring

Climate change predicts harsher summer droughts for mid-latitudes in Europe. To enhance our understanding of the putative impacts on forest regeneration, we studied the response of oak seedlings (Quercus petraea) to water deficit. Potted seedlings originating from three locally sourced provenances were subjected to two successive drought periods during the first growing season each followed by a plentiful re-watering. Here, we describe survival and phenological responses after the second drought treatment, applying general linear mixed modeling. From the 441 drought treated seedlings 189 subsisted with higher chances of survival among smaller plants and among single plants per pot compared to doubles. Remarkably, survival was independent of the provenance, although relatively more plants had died off in two provenances compared to the third one with mean plant height being higher in one provenance and standard deviation of plant height being higher in the other. Timing of leaf senescence was clearly delayed after the severe drought treatment followed by re-watering, with two seedlings per pot showing a lesser retardation compared to single plants. This delay can be interpreted as a compensation time in which plants recover before entering the subsequent developmental process of leaf senescence, although it renders seedlings more vulnerable to early autumn frosts because of the delayed hardening of the shoots. Onset of bud flush in the subsequent spring still showed a significant but small delay in the drought treated group, independent of the number of seedlings per pot, and can be considered as an after effect of the delayed senescence. In both phenological models significant differences among the three provenances were detected independent from the treatment. The only provenance that is believed to be local of origin, displayed the earliest leaf senescence and the latest flushing, suggesting an adaptation to the local maritime climate. This provenance also displayed the highest standard deviation of plant height, which can be interpreted as an adaptation to variable and unpredictable weather conditions, favoring smaller plants in drought-prone summers and higher plants in more normal growing seasons.

Effects of population structure on pollen flow, clonality rates and reproductive success in fragmented Serapias lingua populations

BACKGROUND

Fragmentation of habitats by roads, railroads, fields, buildings and other human activities can affect population size, pollination success, sexual and asexual reproduction specially in plants showing pollinator limitation, such as Mediterranean orchids. In this study, we assessed pollen flow, selfing rates, vegetative reproduction and female reproductive success and their correlations with habitat characters in nine fragmented subpopulations of Serapias lingua. To improve understanding of population structure effects on plant biology, we examined genetic differentiation among populations, pollen flow, selfing rates and clonal reproduction using nuclear microsatellite markers.

RESULTS

Smaller populations showed a significant heterozygote deficit occurred at all five nuclear microsatellite loci, the coefficient of genetic differentiation among populations was 0.053 and pairwise FST was significantly correlated with the geographical distance between populations. Paternity analysis of seeds showed that most pollen flow occurred within a population and there was a positive correlation between percentage of received pollen and distance between populations. The fruit production rate varied between 5.10 % and 20.30 % and increased with increasing population size, while the percentage of viable seeds (78-85 %) did not differ significantly among populations. The extent of clonality together with the clonal and sexual reproductive strategies varied greatly among the nine populations and correlated with the habitats where they occur. The small, isolated populations tended to have high clonal diversity and low fruit production, whereas the large populations with little disturbance were prone to have reductions in clonal growth and increased sexual reproduction.

CONCLUSIONS

We found that clonality offers an advantage in small and isolated populations of S. lingua, where clones may have a greater ability to persist than sexually reproducing individuals.