Temperate Origin Research Articles

Spatial patterns and climatic drivers of phylogenetic structure of regional liverwort assemblages in China.

Latitudinal diversity gradients have been intimately linked to the tropical niche conservatism hypothesis, which posits that there has been a strong filter due to the challenges faced by ancestral tropical lineages to adapt to low temperatures and colonize extra-tropical regions. In liverworts, species richness is higher towards the tropics, but the centres of diversity of the basal lineages are distributed across extra-tropical regions, pointing to the colonization of tropical regions by phylogenetically clustered assemblages of species of temperate origin. Here, we test this hypothesis through analyses of the relationship between macroclimatic variation and phylogenetic diversity in Chinese liverworts. Phylogenetic diversity metrics and their standardized effect sizes for liverworts in each of the 28 regional floras at the province level in China were related to latitude and six climate variables using regression analysis. We conducted variation partitioning analyses to determine the relative importance of each group of climatic variables. We find that the number of species decreases with latitude, whereas phylogenetic diversity shows the reverse pattern, and that phylogenetic diversity is more strongly correlated with temperature-related variables compared with precipitation-related variables. We interpret the opposite patterns observed in phylogenetic diversity and species richness in terms of a more recent origin of tropical diversity coupled with higher extinctions in temperate regions.

Studies on the Vascular Flora of Anaimudi and the Surrounding Regions, Kottayam District, Kerala

The paper deals with an account of the vegetation of Anaimudi (2,695 m) - the highest peak in the peninsular India - and the surrounding regions situated in the Kottayam District of Kerala. The above area has not received much attention in the detailed studies undertaken by various workers on the vegetation of the South Indian hill tops. Based on the explorations carried out by the authors during the years 1965-70, 317 taxa of vascular plants, under 233 genera and 101 families, are enumerated. An analysis of the distribution pattern of the shola and grassland species has shown that (1) the shola species are mainly of tropical stock, (2) quite a number of species on the shola fringes and the grassland are of temperate origin and (3) the temperate elements play a comparatively less important role in the composition of the vegetation at the higher altitudes (above 1,925 m), and that the predominent elements here are of tropical stock. The high incidence of endemic taxa in this region has been pointed out. Literature on the ecological status of the shola-grassland formation has been reviewed for a better understanding of the vegetation.

A leading-edge scenario in the phylogeography and evolutionary history of East Asian insular Taxus in Taiwan and the Philippines.

The cool temperate origin of gymnosperm Taxus species in East Asia is specifically diverse and widespread. Certain lineages have managed to extend their distribution further south to subtropical and tropical islands such as Taiwan and the Philippines. To address questions including whether these insular lineages, recently identified as T. phytonii, have become genetically distinct from each other and from their continental relatives, and when and how they colonized their residing islands, we sampled over 11 populations, covering 179 Taxus individuals from Taiwan and the Philippines. Using four cpDNA and one nuclear marker, we showed in population genetic and genealogical analyses that the two insular lineages were genetically distinct from each other and also from other continental Taxus and that they represented each other's closest relative. Estimated with the coalescent-based multi-type tree (MTT) analyses, we inferred an origin of Taiwanese T. phytonii more ancient than 2.49Mya and that of Philippine T. phytonii more ancient than 1.08Mya. In addition, the divergence demographic history revealed by both MTT and isolation with migration (IM) analyses indicated the presence of recent post-split migrations from a continental taxon, T. mairei, to Taiwanese T. phytonii, as well as from Taiwanese T. phytonii to Philippine T. phytonii. Overall, this study suggests Taiwan as a stepping stone through which the temperate-origin yew trees can extend their distributions to tropical regions such as the Philippines.

Phylogeny, chronology, and phylogeography in Australasian Hypnodendraceae

Abstract The Hypnodendrales form the sister group to all other pleurcarpous mosses in the superorder Hypnanae. Many species are closely associated with the cool temperate rainforests of Australasia, while others are widespread in higher altitude wet forests across tropical South-East Asia. Several of the Malesian entities are taxonomically ambiguous, having been variously treated as species complexes or as single very variable species. Here we use dated phylogenies to examine the timing of diversification of major clades within the Hypnodendrales, test the hypothesis that widespread, taxonomically problematic species have diversified relatively recently in South-East Asia from within clades of southern temperate origin, and address taxonomic questions within Hypnodendron. A chronogram with broad taxonomic sampling is constructed, followed by a second dated phylogeny with dense sampling from Hypnodendron vitiense, a representative morphologically variable species found throughout Eastern Australia and South-East Asia. The crown group Hypnodendrales are found to have originated in the mid-Cretaceous, although they share a Most Recent Common Ancestor (MRCA) with the other Hypnanae in the late Jurassic. Extant members of Hypnodendron share a MRCA ±28 Mya, a little before the start of the collision of Australia with the Sunda plate that initiated the Australasian–Malesian floristic interchange. Within H. vitiense, there is strong phylogenetic structure consistent with the diversification and isolation of populations in South-East Asia within the last 10 Mya. The New Zealand endemic H. marginatum is found to be derived from within an Australasian clade of H. vitiense, this in turn being distinct from a South-East Asian/tropical Australian H. vitiense clade. Our results suggest that the phylogeography of this prominent group of mosses closely mirrors that of the rainforest ecosystems of which they are a part.

New liguleless (lg2) maize stocks: Genetic resources for leaf architectural and haploid induction rate assessment studies

AbstractLiguleless mutants produce defective ligules and auricles and, consequently, have more upright leaves than their ligulate counterparts, making them useful genetic material for plant architectural studies. Besides, owing to the recessive nature and amenability of the liguleless trait to phenotyping at the seedling stage, liguleless mutants are popularly used for ‘proof‐of‐concept’ demonstration and assessment of haploid induction rate (HIR) of haploid inducer lines (HILs) in maize. The commonly used liguleless testers in maize are of temperate origin and are challenging to use and maintain under tropical/sub‐tropical conditions. In the present study, liguleless lines (V 601, V 602, V 603 and V 604) derived from crosses between agronomically superior locally adapted tropical ligulate lines (V 407 and CM 152) and liguleless donors of temperate origin (PDH‐3 and PDH‐8) were evaluated for different agro‐morphological traits. Liguleless line V 602 was also used as a tester to assess the HIR of haploid inducer line EC937890 (CIM2GTAILP2). The results showed a mean HIR of 12.42% for EC937890, consistent with the HIR reported in other studies, thus demonstrating the efficacy of V 602 as a tester for determining HIR. The agronomically superior liguleless maize lines reported in this study will, therefore, be a valuable resource for leaf architectural studies, assessment of HIR of candidate HILs and maintenance of high HIR in the HILs presently in wide use in the doubled haploid (DH) programmes. Additionally, these genetic stocks carry the liguleless trait in genetic backgrounds with known heterotic affinity with early maturity Indian public maize germplasm and, therefore, can be used directly as parents in hybrid development programmes.

Popcorn (Zea mays L. var. Everta) haploids identified by Navajo phenotype and ploidy level.

For popcorn, obtaining and identifying haploids are still challenging steps. We aimed to induce and screen haploids in popcorn using the Navajo phenotype, seedling vigor, and ploidy level. We used the Krasnodar Haploid Inducer (KHI) in crosses with 20 popcorn source germplasms and five maize controls. The field trial design was completely randomized, with three replications. We assessed the efficacy of induction and identification of haploids based on the haploidy induction rate (HIR) and false positive and negative rates (FPR and FNR). Additionally, we also measured the penetrance of the Navajo marker gene (R1-nj). All putative haploids classified by the R1-nj were germinated together with a diploid sample and evaluated for false positives and negatives based on vigor. Seedlings from 14 females were submitted to flow cytometry to determine the ploidy level. The HIR and penetrance were analyzed by fitting a generalized linear model with a logit link function. The HIR of the KHI, adjusted by cytometry, ranged from 0.0 to 1.2%, with a mean of 0.34%. The average FPR from screening based on the Navajo phenotype was 26.2% and 76.4% for vigor and ploidy, respectively. The FNR was zero. The penetrance of R1-nj ranged from 30.8 to 98.6%. The average number of seeds per ear in temperate germplasm (76) was lower than that obtained in tropical germplasm (98). There is an induction of haploids in germplasm of tropical and temperate origin. We recommend the selection of haploids associated with the Navajo phenotype with a direct method of confirming the ploidy level, such as flow cytometry. We also show that haploid screening based on Navajo phenotype and seedling vigor reduces misclassification. The origin and genetic background of the source germplasm influence the R1-nj penetrance. Because the known inducers are maize, developing doubled haploid technology for popcorn hybrid breeding requires overcoming unilateral cross-incompatibility.

Body Condition in the Tawny Owl Strix aluco near the Northern Limit of Its Range: Effects of Individual Characteristics and Environmental Conditions.

Simple SummaryThe present study examines how the variations in food supply and winter weather are reflected in the body condition of female and male Tawny Owls Strix aluco of different colour morphs in a population near the southern coast of Finland. Winter weather conditions before breeding seemed to have effects on the food availability of Tawny Owls: the depth of the snow cover showed a positive relationship, and the frequency of temperature fluctuations around the freezing point had a negative relationship. In females, intrinsic factors such as colour morph and age, as well as the body condition of the mate and the stage of the season, governed body condition. In males, only age and the stage of the season suggested associations with body condition. Probably due to the efficient use of alternative prey, the effects of fluctuations of vole populations on the body condition of Tawny Owls are only moderate.The body condition of boreal species of vole-eaters seems to vary largely according to fluctuations in vole populations and weather conditions of the preceding winter. I studied females and males of the Tawny Owl Strix aluco of temperate origin near the northern limit of the species’ range in southern Finland to reveal if they show similar patterns to the boreal species. Winter weather conditions before breeding seemed to have pronounced effects on the food availability of Tawny Owls. In females, intrinsic factors such as colour morph and age, as well as the body condition of the mate and the stage of the season (Julian date), governed body condition. In males, only age and Julian date showed pronounced relationships with body condition. The results suggest that deep snow cover protects vole populations through winter until spring better than a minor amount of snow and that frequent temperature fluctuations around the freezing point in early spring make voles more available for owls that are preparing for breeding. This was also reflected positively in the body condition of female owls. Probably due to the efficient use of alternative prey, the effects of fluctuating vole populations on the body condition of Tawny Owls are, in general, only moderate.

Rapid Adjustments in Thermal Tolerance and the Metabolome to Daily Environmental Changes - A Field Study on the Arctic Seed Bug Nysius groenlandicus.

Laboratory investigations on terrestrial model-species, typically of temperate origin, have demonstrated that terrestrial ectotherms can cope with daily temperature variations through rapid hardening responses. However, few studies have investigated this ability and its physiological basis in the field. Especially in polar regions, where the temporal and spatial temperature variations can be extreme, are hardening responses expected to be important. Here, we examined diurnal adjustments in heat and cold tolerance in the Greenlandic seed bug Nysius groenlandicus by collecting individuals for thermal assessment at different time points within and across days. We found a significant correlation between observed heat or cold tolerance and the ambient microhabitat temperatures at the time of capture, indicating that N. groenlandicus continuously and within short time-windows respond physiologically to thermal changes and/or other environmental variables in their microhabitats. Secondly, we assessed underlying metabolomic fingerprints using GC-MS metabolomics in a subset of individuals collected during days with either low or high temperature variation. Concentrations of metabolites, including sugars, polyols, and free amino acids varied significantly with time of collection. For instance, we detected elevated sugar levels in animals caught at the lowest daily field temperatures. Polyol concentrations were lower in individuals collected in the morning and evening and higher at midday and afternoon, possibly reflecting changes in temperature. Additionally, changes in concentrations of metabolites associated with energetic metabolism were observed across collection times. Our findings suggest that in these extreme polar environments hardening responses are marked and likely play a crucial role for coping with microhabitat temperature variation on a daily scale, and that metabolite levels are actively altered on a daily basis.

Genetic basis and adaptation trajectory of soybean from its temperate origin to tropics

Soybean (Glycine max) serves as a major source of protein and edible oils worldwide. The genetic and genomic bases of the adaptation of soybean to tropical regions remain largely unclear. Here, we identify the novel locus Time of Flowering 16 (Tof16), which confers delay flowering and improve yield at low latitudes and determines that it harbors the soybean homolog of LATE ELONGATED HYPOCOTYL (LHY). Tof16 and the previously identified J locus genetically additively but independently control yield under short-day conditions. More than 80% accessions in low latitude harbor the mutations of tof16 and j, which suggests that loss of functions of Tof16 and J are the major genetic basis of soybean adaptation into tropics. We suggest that maturity and yield traits can be quantitatively improved by modulating the genetic complexity of various alleles of the LHY homologs, J and E1. Our findings uncover the adaptation trajectory of soybean from its temperate origin to the tropics.

Cold Survival and Its Molecular Mechanisms in a Locally Adapted Nematode Population.

Since Darwin, evolutionary biologists have sought to understand the drivers and mechanisms of natural trait diversity. The field advances toward this goal with the discovery of phenotypes that vary in the wild, their relationship to ecology, and their underlying genes. Here, we established resistance to extreme low temperature in the free-living nematode Caenorhabditis briggsae as an ecological and evolutionary model system. We found that C. briggsae strains of temperate origin were strikingly more cold-resistant than those isolated from tropical localities. Transcriptional profiling revealed expression patterns unique to the resistant temperate ecotype, including dozens of genes expressed at high levels even after multiple days of cold-induced physiological slowdown. Mutational analysis validated a role in cold resistance for seven such genes. These findings highlight a candidate case of robust, genetically complex adaptation in an emerging model nematode, and shed light on the mechanisms at play.

Full-length transcriptome profiling reveals insight into the cold response of two kiwifruit genotypes (A. arguta) with contrasting freezing tolerances

BackgroundKiwifruit (Actinidia Lindl.) is considered an important fruit species worldwide. Due to its temperate origin, this species is highly vulnerable to freezing injury while under low-temperature stress. To obtain further knowledge of the mechanism underlying freezing tolerance, we carried out a hybrid transcriptome analysis of two A. arguta (Actinidi arguta) genotypes, KL and RB, whose freezing tolerance is high and low, respectively. Both genotypes were subjected to − 25 °C for 0 h, 1 h, and 4 h.ResultsSMRT (single-molecule real-time) RNA-seq data were assembled using the de novo method, producing 24,306 unigenes with an N50 value of 1834 bp. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of DEGs showed that they were involved in the ‘starch and sucrose metabolism’, the ‘mitogen-activated protein kinase (MAPK) signaling pathway’, the ‘phosphatidylinositol signaling system’, the ‘inositol phosphate metabolism’, and the ‘plant hormone signal transduction’. In particular, for ‘starch and sucrose metabolism’, we identified 3 key genes involved in cellulose degradation, trehalose synthesis, and starch degradation processes. Moreover, the activities of beta-GC (beta-glucosidase), TPS (trehalose-6-phosphate synthase), and BAM (beta-amylase), encoded by the abovementioned 3 key genes, were enhanced by cold stress. Three transcription factors (TFs) belonging to the AP2/ERF, bHLH (basic helix-loop-helix), and MYB families were involved in the low-temperature response. Furthermore, weighted gene coexpression network analysis (WGCNA) indicated that beta-GC, TPS5, and BAM3.1 were the key genes involved in the cold response and were highly coexpressed together with the CBF3, MYC2, and MYB44 genes.ConclusionsCold stress led various changes in kiwifruit, the ‘phosphatidylinositol signaling system’, ‘inositol phosphate metabolism’, ‘MAPK signaling pathway’, ‘plant hormone signal transduction’, and ‘starch and sucrose metabolism’ processes were significantly affected by low temperature. Moreover, starch and sucrose metabolism may be the key pathway for tolerant kiwifruit to resist low temperature damages. These results increase our understanding of the complex mechanisms involved in the freezing tolerance of kiwifruit under cold stress and reveal a series of candidate genes for use in breeding new cultivars with enhanced freezing tolerance.

Acorn characteristics, seed germination, seedling development, and leaf traits of three oak species from Talamanca, Costa Rica1

Three oak species dominate the mature montane cloud forests in the Talamanca mountain range, Costa Rica. These oak species exist at different elevations and encounter increasing soil and atmospheric stress conditions as elevation increases along a gradient (2,000–3,200 m). We compared acorn characteristics, seed germination, seedling morphology, and leaf morphology of these three oak species to determine if these traits varied along this elevation gradient. Seeds were measured, weighed, and examined for viability and germination. Seeds were planted in a common garden at 2,700 m to evaluate seedling development, morphology, and growth. We found that seeds had high water content and germination patterns typical of the recalcitrant syndrome. Quercus costaricensis acorns were bigger and had higher viability and seed germination than acorns and seeds of Quercus salicifolia and Quercus bumelioides. However, seeds from the smaller acorns of Q. salicifolia and Q. bumelioides were not less prone to germinate than Q. costaricensis. Germination was of the phanerocotylar-semihypogeal-reserve type, consistent with the temperate origin of the genus. The developing seedlings produced a leafy crown and a vigorous adventitious root system soon after germination. Together, these new organs allow seedlings to substitute or complement the resources provided by the fleshy cotyledons. Leaves of Q. costaricensis seedlings (from the highest elevation) were smaller, darker, and thicker than those of Q. bumelioides and Q. salicifolia. However, there were no differences in leaf mass per area among seedlings of different species. We discuss the importance of interspecific differences in seedling growth resulting from seed size differences and environmental heterogeneity for niche segregation and the observed distribution of Q. salicifolia, Q. bumelioides, and Q. costaricensis along the elevation gradient.

Unravelling foliar water uptake pathways: The contribution of stomata and the cuticle.

Plants can absorb water through their leaf surfaces, a phenomenon commonly referred to as foliar water uptake (FWU). Despite the physiological importance of FWU, the pathways and mechanisms underlying the process are not well known. Using a novel experimental approach, we parsed out the contribution of the stomata and the cuticle to FWU in two species with Mediterranean (Prunus dulcis) and temperate (Pyrus communis) origin. The hydraulic parameters of FWU were derived by analysing mass and water potential changes of leaves placed in a fog chamber. Leaves were previously treated with abscisic acid to force stomata to remain closed, with fusicoccin to remain open, and with water (control). Leaves with open stomata rehydrated two times faster than leaves with closed stomata and attained approximately three times higher maximum fluxes and hydraulic conductance. Based on FWU rates, we propose that rehydration through stomata occurs primarily via diffusion of water vapour rather than in liquid form even when leaf surfaces are covered with a water film. We discuss the potential mechanisms of FWU and the significance of both stomatal and cuticular pathways for plant productivity and survival.

ISSR Analysis Reveals High Genetic Variation in Strawberry Three-Way Hybrids Developed for Tropical Regions

The cultivated strawberry (Fragaria × ananassa Duch.) is a species of temperate origin, and the extension of this crop into tropical regions is dependent on genetic breeding. Breeders in the UNICENTRO’s Strawberry Breeding Program (USBP) selected, from among 2,000 hybrids, 40 hybrids that were adapted to photoperiod and temperature conditions of tropical regions. In this study, we used inter-simple sequence repeat to characterize 40 three-way hybrids developed by USBP and evaluated the genetic relationship of these hybrids with commercial cultivars, heirloom cultivars, and single hybrids. We used nine inter-simple sequence repeat primers to genotype 14 commercial cultivars, five heirloom cultivars, five single hybrids (SH), 20 three-way hybrids with short-day behavior (SDH), and 20 three-way hybrids with photoperiod-insensitive behavior (PIH). The percentage of polymorphism (100%) and both, the Nei genetic diversity (h = 0.34) and the Shannon index (I = 0.51), showed high variability and diversity, respectively, in the evaluated strawberry genotypes. Commercial cultivars showed the highest diversity indices (h = 0.30, I = 0.46), followed by PIH hybrids (h = 0.27, I = 0.41). In the dendrogram, the genotypes were distributed into three groups (commercial cultivars, heirloom cultivars, and single hybrids; SDH and PIH). This clustering was confirmed by principal coordinate analysis and Bayesian inference analysis. The overall analysis of the data revealed the efficacy of USBP in three-way hybrid development with different genetic characteristics compared with those of available commercially cultivars. These hybrids have substantial potential in becoming new strawberry cultivars.

Diversity and Distribution of the Dominant Ant Genus Anonychomyrma (Hymenoptera: Formicidae) in the Australian Wet Tropics

Anonychomyrma is a dolichoderine ant genus of cool-temperate Gondwanan origin with a current distribution that extends from the north of southern Australia into the Australasian tropics. Despite its abundance and ecological dominance, little is known of its species diversity and distribution throughout its range. Here, we describe the diversity and distribution of Anonychomyrma in the Australian Wet Tropics bioregion, where only two of the many putative species are described. We hypothesise that the genus in tropical Australia retains a preference for cool wet rainforests reminiscent of the Gondwanan forests that once dominated Australia, but now only exist in upland habitats of the Wet Tropics. Our study was based on extensive recent surveys across five subregions and along elevation and vertical (arboreal) gradients. We integrated genetic (CO1) data with morphology to recognise 22 species among our samples, 20 of which appeared to be undescribed. As predicted, diversity and endemism were concentrated in uplands above 900 m a.s.l. Distribution modelling of the nine commonest species identified maximum temperature of the warmest month, rainfall seasonality, and rainfall of the wettest month as correlates of distributional patterns across subregions. Our study supported the notion that Anonychomyrma radiated from a southern temperate origin into the tropical zone, with a preference for areas of montane rainforest that were stably cool and wet over the late quaternary.

Modeling Phylogenetic Biome Shifts on a Planet with a Past.

The spatial distribution of biomes has changed considerably over deep time, so the geographical opportunity for an evolutionary lineage to shift into a new biome may depend on how the availability and connectivity of biomes has varied temporally. To better understand how lineages shift between biomes in space and time, we developed a phylogenetic biome shift model in which each lineage shifts between biomes and disperses between regions at rates that depend on the lineage's biome affinity and location relative to the spatial distribution of biomes at any given time. To study the behavior of the biome shift model in an empirical setting, we developed a literature-based representation of paleobiome structure for three mesic forest biomes, six regions, and eight time strata, ranging from the Late Cretaceous (100 Ma) through the present. We then fitted the model to a time-calibrated phylogeny of 119 Viburnum species to compare how the results responded to various realistic or unrealistic assumptions about paleobiome structure. Ancestral biome estimates that account for paleobiome dynamics reconstructed a warm temperate (or tropical) origin of Viburnum, which is consistent with previous fossil-based estimates of ancestral biomes. Imposing unrealistic paleobiome distributions led to ancestral biome estimates that eliminated support for tropical origins, and instead inflated support for cold temperate ancestry throughout the warmer Paleocene and Eocene. The biome shift model we describe is applicable to the study of evolutionary systems beyond Viburnum, and the core mechanisms of our model are extensible to the design of richer phylogenetic models of historical biogeography and/or lineage diversification. We conclude that biome shift models that account for dynamic geographical opportunities are important for inferring ancestral biomes that are compatible with our understanding of Earth history.[Ancestral states; biome shifts; historical biogeography; niche conservatism; phylogenetics].

Tree species of tropical and temperate lineages in a tropical Asian montane forest show different range dynamics in response to climate change

Shifts in species distributions have been documented in response to recent climatic change, with most species moving poleward and to higher altitude. However, different taxa may respond to climatic change differently. The Climatic Variability Hypothesis (CVH) suggests that taxa originating from environmentally variable habitats, such as those at high latitudes and altitudes, should evolve wider environmental tolerances and greater dispersal capacity, and consequently be less responsive to climatic change than taxa originating from relatively stable habitats. However, empirical tests of this hypothesis, especially in the Asian tropics, are scarce. In this study, we assessed the range dynamics of 20 tree species, by using the abundance and mean tree diameter and the ratio of juveniles to trees along an altitudinal transect (2450 m–3070 m) in a montane forest located in the southeastern Himalayas in Myanmar. We also compared the suitable range sizes of tree species of different range dynamics category. Among the species investigated, 12 experienced significant upward range extensions and other eight species experienced no-upward extensions. The modeled distribution range size of the ‘upward species’ were marginally significant narrower than those of ‘non-upward’ species. The ‘upward’ species were also often species of tropical evolutionary origin and the ‘non-upward’ species were of subtropics and temperate origin. The mechanism behind these distribution patterns of different species may be complex while the distribution patterns of this 20 species along the altitudinal transect generally support the prediction of the CVH. From the perspective of conserving biodiversity against the impacts of climatic change, more attention needs to be paid to narrowly distributed species, which are typically tropical origin, by enhancing connectivity and dispersal capacity in fragmented landscapes.

Responses to chilling of recalcitrant seeds of Ekebergia capensis from different provenances

Recalcitrant seeds are shed at relatively high water contents and are metabolically active, initiating germination without exogenous provision of water. For whole seeds, specialised storage under hydrated conditions at the lowest possible temperatures not having adverse consequences, is required. This study aimed to establish the effect of chilling on the recalcitrant seeds of a single species, Ekebergia capensis, from three different populations occurring in different climates. These were collected from temperate Port Elizabeth (PE; Eastern Cape), sub-tropical St Lucia (KwaZulu-Natal [KZN]) and Tanzania (tropical southern Africa). Viability, axis ultrastructure, solute leakage and protein synthesis were assessed as indicators of response to chilling. These parameters were measured at intervals during storage under hydrated conditions. The seeds from PE retained 80% viability after 12 weeks in storage at 1° and 3 °C and 100% when stored at 6 °C. Those from St Lucia were dead after 38 d in storage at 3 °C, but had retained 100% viability at 6° and 16 °C for the same period. In contrast, all the seeds from Tanzania were dead after 9 d when stored at 3 °C and retained only 10 and 35% viability when stored for 9 d at 6° and 16 °C, respectively. A reduced rate of protein synthesis and increased solute leakage in axes during storage implied a breakdown in metabolic activity. Upon establishing that the PE seeds tolerated slow drying, it is suggested these seeds might be considered to be minimally recalcitrant. Studies of variation in nuclear ribosomal ITS1 sequences revealed the presence of three well-to-strongly-supported monophyletic clades corresponding to the geographical areas from which the seeds were sampled (PE, KZN and Tanzania). Observations indicated that axes from the seeds originating in St Lucia and Tanzania lost ultrastructural integrity when stored at 3 °C. Axes from the PE seeds did not show any deterioration in ultrastructure – for relatively prolonged storage periods. It is clear from the present study, that E. capensis seeds of temperate (PE) origin do tolerate chilling temperatures well, whereas those from sub-tropical St Lucia or the tropical Tanzanian provenance, do not. It is probable that what has been tacitly assumed to be a single species, may not be so.

Winter Injury to Grapevine Secondary Phloem and Cambium Impairs Budbreak, Cambium Activity, and Yield Formation

Vitis vinifera is a species of temperate origin that reactivates the dormant secondary phloem from the previous year at the resumption of growth in spring. Following harsh winters, grapevines may display a set of symptoms including delayed and heterogeneous budbreak, dieback with shoot renewal from the trunk base or sudden death of the plant. Although it was suggested that these symptoms may be associated with freeze damage to the secondary phloem, there is no experimental evidence that quantifies tissue responses to freezing and their consequences for the plant. This work evaluated how different severities of cold damage to the secondary phloem during the dormant season impacted the anatomical, physiological, and agronomic responses of grapevines during the subsequent growing season. Single-node cane sections were subjected to a range of freezing temperatures that damaged only the phloem, and changes in anatomy and physiology were monitored. In addition, the consequences of natural winter freezes for yield formation of field-grown plants were evaluated. Our results suggest that the more severe a freeze event is, the greater will be the degree of secondary phloem disorganization, leading to delays in budbreak and subsequent phenological stages, and in cambial activity. Winter freezes also led to a loss of plant vigor and a reduction in cluster number, berries per cluster, and fruit sugar content. We conclude that winter freeze events can produce hidden damage in grapevine perennial tissues, which may compromise subsequent growth and productivity depending on the severity of the damage.

Tolerance of three Aedes albopictus strains (Diptera: Culicidae) from different geographical origins towards winter temperatures under field conditions in northern Germany.

The continuing spread of the Asian tiger mosquito Aedes albopictus, a vector of many arboviruses and some dirofilarial worms, in Europe calls for advanced investigations on its ecological ability to establish and overwinter in temperate, more northern geographic regions. To meet this purpose, eggs of Ae. albopictus laboratory strains of tropical, subtropical and temperate origin were exposed to field conditions during one or two winter seasons in northeastern Germany. After 1 to 16 weeks of outdoor exposure, eggs were flooded in the laboratory, and the hatching rates were determined. During the winter season 2015/2016, when temperatures reached –10°C, the subtropical strain showed hatching after all time periods while the tropical strain displayed hatching only until two weeks of cold exposure. In the winter season 2016/2017, with temperatures as low as ‒6°C, all three strains produced hatching larvae after all time periods. Both the hatching rates and the hatching behaviour differed between the strains. Larvae of the subtropical and temperate strains hatched in installments over a period of four weeks while the larvae of the tropical strain hatched within a short time period, often one week. The results of the study demonstrate that Ae. albopictus strains of different, even tropical, origin might be able to survive a central European winter, although this is likely to depend on the specific course of the temperatures. Further studies with different temperature regimes and different mosquito strains are needed to specify these findings.