Sources of resistance to grapevine fanleaf virus (GFV) in Vitis species

A diverse array of Vitis germplasm was screened to identify sources of resistance to grapevine fanleaf virus (GFV). The 173 accessions screened included Vitis species, cultivars, and interspecific hybrids. Since Vitis vinifera and GFV are thought to have a common origin in the Middle East, particular attention was paid to this species - 27 Middle Eastern vinifera accessions and 9 vinifera cultivars were surveyed. In addition, North American accessions of 24 Euvitis species and 2 Muscadinia species were tested, including cultivars of rotundifolia, as were accessions of 5 Asian species. The interspecific hybrids included 3 vinifera x rotundifolia (VR) hybrids known to be resistant to the feeding of Xiphinema index, the nematode vector of GFV. The vines to be tested were approach grafted to infected Cabernet Sauvignon vines and subsequently screened for the presence of the virus by ELISA. 3 GFV-resistant accessions were identified - a Middle Eastern vinifera, rotundifolia cv. Bountiful, and one of the VR hybrids. Several vinifera accessions (including some cultivars) previously reported to be GFV-resistant were susceptible in this study. These results suggest that two forms of GFV resistance, hast plant resistance and nonhost resistance, exist in Vitis germplasm

Zero-sum, the niche,and metacommunities: long-term dynamics of community assembly

Recent models of community assembly, structure, and dynamics have incorporated, to varying degrees, three mechanistic processes: resource limitation and interspecific competition, niche requirements of species, and exchanges between a local community and a regional species pool. Synthesizing 30 years of data from an intensively studied desert rodent community, we show that all of these processes, separately and in combination, have influenced the structural organization of this community and affected its dynamical response to both natural environmental changes and experimental perturbations. In addition, our analyses suggest that zero-sum constraints, niche differences, and metacommunity processes are inextricably linked in the ways that they affect the structure and dynamics of this system. Explicit consideration of the interaction of these processes should yield a deeper understanding of the assembly and dynamics of other ecological communities. This synthesis highlights the role that long-term data, especially when coupled with experimental manipulations, can play in assessing the fundamental processes that govern the structure and function of ecological communities

Effects of mammalian herbivore declines on plant communities: observations and experiments in an African savanna

1. Herbivores influence the structure and composition of terrestrial plant communities. However, responses of plant communities to herbivory are variable and depend on environmental conditions, herbivore identity and herbivore abundance. As anthropogenic impacts continue to drive large declines in wild herbivores, understanding the context dependence of herbivore impacts on plant communities becomes increasingly important. 2. Exclosure experiments are frequently used to assess how ecosystems reorganize in the face of large wild herbivore defaunation. Yet in many landscapes, declines in large wildlife are often accompanied by other anthropogenic activities, especially land conversion to livestock production. In such cases, exclosure experiments may not reflect typical outcomes of human-driven extirpations of wild herbivores. 3. Here, we examine how plant community responses to changes in the identity and abundance of large herbivores interact with abiotic factors (rainfall and soil properties). We also explore how effects of wild herbivores on plant communities differ between large-scale herbivore exclosures and landscape sites where anthropogenic activity has caused wildlife declines, often accompanied by livestock increases. 4. Abiotic context modulated the responses of plant communities to herbivore declines with stronger effect sizes in lower-productivity environments. Also, shifts in plant community structure, composition and species richness following wildlife declines differed considerably between exclosure experiments and landscape sites in which wild herbivores had declined and were often replaced by livestock. Plant communities in low wildlife landscape sites were distinct in both composition and physical structure from both exclosure and control sites in experiments. The power of environmental (soil and rainfall) gradients in influencing plant response to herbivores was also greatly dampened or absent in the landscape sites. One likely explanation for these observed differences is the compensatory effect of livestock associated with the depression or extirpation of wildlife. 5. Synthesis. Our results emphasize the importance of abiotic environmental heterogeneity in modulating the effects of mammalian herbivory on plant communities and the importance of such covariation in understanding effects of wild herbivore declines. They also suggest caution when extrapolating results from exclosure experiments to predict the consequences of defaunation as it proceeds in the Anthropocene

First Report of Phytophthora occultans Causing Root and Collar Rot on Ceanothus, Boxwood, Rhododendron, and Other Hosts in Horticultural Nurseries in Oregon, USA

Dead and dying Ceanothus sanguineus, C. velutinus, and C. integerrimus plants grown in a native plant nursery in Oregon for landscape restoration were reported in 2011. Plants were wilted with stem lesions above necrotic roots. Using selective media (Hansen et al. 2012), twelve similar Phytophthora isolates were obtained. DNA sequences of the cox 1, β tubulin, and the rDNA ITS regions were generated (Hansen et al. 2012). All isolates had identical ITS sequences (GenBank KP742989), and were identical to Phytophthora occultans (Man in’t Veld et al. 2014) (JX978155) and 99% similar to P. himalsilva (HM752784) in a BLAST analysis. They were also identical to P. occultans in cox 1 and β tubulin (KR028484 and KR028483). Isolates were homothallic, with smooth 30-µm-diameter oogonia, and slightly aplerotic oospores. Antheridia were mostly paragynous. Colonies were stellate on carrot agar, growing 6 to 7 mm/d at optimum temperature (25°C). Sporangia were ovoid to irregular and papillate. Morphology and growth were consistent with P. occultans. Collections of unidentified Phytophthora spp. from the OSU Plant Clinic and from other Oregon nurseries (J. Parke et al. 2014) revealed additional isolates with similar morphology and identical DNA sequences. P. occultans was identified from boxwood (Buxus spp.), rhododendron, Gaultheria shallon, Arctostaphylos uva-ursi, and Mahonia nervosa in addition to Ceanothus spp. Two inoculation trials were conducted: (i) Healthy 1-year-old plants of C. sanguineus and C. velutinus were stem wound inoculated with two isolates of P. occultans from Ceanothus, or with sterile agar. There were 3 to 5 replications for each host and the control. The test was repeated with addition of two isolates from boxwood. (ii) Boxwood (B. sempervirens) and rhododendron (R. catawbiense Alba) were stem wound inoculated with two isolates each of P. occultans from Ceanothus and boxwood. There were four replications of each host for each isolate. All plants were incubated at 20 to 22°C. In test 1, all isolates induced stem lesions and wilting on all inoculated plants of both Ceanothus species. Wilting began in 14 days and lesions, measured at 19 days, averaged about 150 mm. There were no symptoms on control plants. In test 2, lesions developed on rhododendron stems, often girdling the stem within 12 days. Most boxwood showed no foliar symptoms or only mild yellowing, although stem lesions averaging 3.5 cm in 7 weeks were present on all plants. P. occultans was reisolated from all hosts in both tests. P. occultans was recently described from Buxus nursery stock in The Netherlands (Man in’t Veld et al. 2014), and isolates with identical DNA sequences were reported from Germany and Romania (Nechwatal et al. 2014). This is the first report from North America. It appears that a single clone of P. occultans recently has been spread widely in the nursery trade. P. occultans is similar to P. himalsilva (Vettraino et al. 2011) and to other members of the poorly defined P. citrophthora clade. Phylogenetic analysis may revise species definitions. Nursery plants grown for wildland restoration are at high risk to carry exotic Phytophthora species into vulnerable landscapes. Forest restoration specialists must demand healthy stock from nurseries

Large herbivores transform plant-pollinator networks in an African savanna

Pollination by animals is a key ecosystem service1,2 and interactions between plants and their pollinators are a model system for studying ecological networks,3,4 yet plant-pollinator networks are typically studied in isolation from the broader ecosystems in which they are embedded. The plants visited by pollinators also interact with other consumer guilds that eat stems, leaves, fruits, or seeds. One such guild, large mammalian herbivores, are well-known ecosystem engineers5, 6, 7 and may have substantial impacts on plant-pollinator networks. Although moderate herbivory can sometimes promote plant diversity,8 potentially benefiting pollinators, large herbivores might alternatively reduce resource availability for pollinators by consuming flowers,9 reducing plant density,10 and promoting somatic regrowth over reproduction.11 The direction and magnitude of such effects may hinge on abiotic context—in particular, rainfall, which modulates the effects of ungulates on vegetation.12 Using a long-term, large-scale experiment replicated across a rainfall gradient in central Kenya, we show that a diverse assemblage of native large herbivores, ranging from 5-kg antelopes to 4,000-kg African elephants, limited resource availability for pollinators by reducing flower abundance and diversity; this in turn resulted in fewer pollinator visits and lower pollinator diversity. Exclusion of large herbivores increased floral-resource abundance and pollinator-assemblage diversity, rendering plant-pollinator networks larger, more functionally redundant, and less vulnerable to pollinator extinction. Our results show that species extrinsic to plant-pollinator interactions can indirectly and strongly alter network structure. Forecasting the effects of environmental change on pollination services and interaction webs more broadly will require accounting for the effects of extrinsic keystone species

Thrombocytogenesis by megakaryocyte; Interpretation by protoplatelet hypothesis

Serial transmission electron microscopy of human megakaryocytes (MKs) revealed their polyploidization and gradual maturation through consecutive transition in characteristics of various organelles and others. At the beginning of differentiation, MK with ploidy 32N, e.g., has 16 centrosomes in the cell center surrounded by 32N nucleus. Each bundle of microtubules (MTs) emanated from the respective centrosome supports and organizes 16 equally volumed cytoplasmic compartments which together compose one single 32N MK. During the differentiation, single centriole separated from the centriole pair, i.e., centrosome, migrates to the most periphery of the cell through MT bundle, corresponding to a half of the interphase array originated from one centrosome, supporting one “putative cytoplasmic compartment” (PCC). Platelet demarcation membrane (DM) is constructed on the boundary surface between neighbouring PCCs. Matured PCC, composing of a tandem array of platelet territories covered by a sheet of DM is designated as protoplatelet. Eventually, the rupture of MK results in release of platelets from protoplatelets

Effects of body size on estimation of mammalian area requirements.

Accurately quantifying species' area requirements is a prerequisite for effective area-based conservation. This typically involves collecting tracking data on species of interest and then conducting home range analyses. Problematically, autocorrelation in tracking data can result in space needs being severely underestimated. Based on the previous work, we hypothesized the magnitude of underestimation varies with body mass, a relationship that could have serious conservation implications. To evaluate this hypothesis for terrestrial mammals, we estimated home-range areas with global positioning system (GPS) locations from 757 individuals across 61 globally distributed mammalian species with body masses ranging from 0.4 to 4000 kg. We then applied blockcross validation to quantify bias in empirical home range estimates. Area requirements of mammals 1, meaning the scaling of the relationship changedsubstantially at the upper end of the mass spectrum