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Tree by Tree is a warning and a toolkit for the future of forest recovery. Scott J. Meiners investigates the critical biological threats endangering tree species native to the forests of eastern North America, providing a needed focus on this plight. Meiners suggests that if we are to save our forests, the first step is to recognize the threats in front of us. Meiners focuses on five familiar trees—the American elm, the American chestnut, the eastern hemlock, the white ash, and the sugar maple—and shares why they matter economically, ecologically, and culturally. From outbreaks of Dutch elm disease to infestations of emerald ash borers, Meiners highlights the challenges that have led or will lead to the disappearance of these trees from forests. In doing so, he shows us how diversity loss often disrupts intricately balanced ecosystems and how vital it is that we pay more attention to massive changes in forest composition. With practical steps for the conservation of native tree species, Tree by Tree offers the inspiration and insights we need to begin saving our forests.

The antimicrobial activity of six plant extracts from Ocimum basilicum, Azadirachta indica, Eucalyptus chamadulonsis, Datura stramonium, Nerium oleander, and Allium sativum was tested for controlling Alternaria solani in vitro and in vivo. In in vitro study the leaf extracts of D. stramonium, A. indica, and A. sativum at 5% concentration caused the highest reduction of mycelial growth of A. solani (44.4, 43.3 and 42.2%, respectively), while O. basilicum at 1% and 5% concentration and N. oleander at 5% concentration caused the lowest inhibition of mycelial growth of the pathogen. In greenhouse experiments the highest reduction of disease severity was achieved by the extracts of A. sativum at 5% concentration and D. stramonium at 1% and 5% concentration. The greatest reduction of disease severity was achieved by A. sativum at 5% concentration and the smallest reduction was obtained when tomato plants were treated with O. basilicum at 1% and 5% concentration (46.1 and 45.2 %, respectively). D. stramonium and A. sativum at 5% concentration increased the fruit yield by 76.2% and 66.7% compared to the infected control. All treatments with plant extracts significantly reduced the early blight disease as well as increased the yield of tomato compared to the infected control under field conditions.

The extent and temporal pattern of crown damage (attributed to Hymenoscyphus pseudoalbidus) in even-aged stands of Fraxinus excelsior in relation to bud flushing phenotype, stand density, and season was investigated. Data were collected in 2007 in four statistically designed thinning experiments located in 12-15-years old plantations of ash in Denmark. The study included 21 plots of four contrasting, residual stand densities: (1) 1,700-5,500 trees/ha (unthinned control plots), (2) 1,500 trees/ha, (3) 500 trees/ha, and (4) 100-150 trees/ha. Assessments included estimation of flushing phenotype in May, followed by evaluation of severity of crown damage (percentage of crown killed) in June and September. Simultaneously, for each tree, the presence or absence of crown wilt and dead tops were recorded. The seasonal pattern of disease severity (average crown damage) was similar in all stands, and disregarding stand density the extent of tree crown damage increased significantly towards the end of the growing season. Disease severity was the worst in unthinned plots, but otherwise unrelated to stand density. Late-flushing trees were most severely affected (P less than 0.001). The observed patterns of disease severity are probably associated with ecological features of the pathogen that still remain largely unknown.

▪ Abstract  Suppression of the blossom-blight phase of fire blight is a key point in the management of this destructive and increasingly important disease of apple and pear. For blossom infection to occur, the causal bacterium, Erwinia amylovora, needs to increase its population size through an epiphytic phase that occurs on stigmatic surfaces. Knowledge of the ecology of the pathogen on stigmas has been key to the development of predictive models for infection and optimal timing of antibiotic sprays. Other bacterial epiphytes also colonize stigmas where they can interact with and suppress epiphytic growth of the pathogen. A commercially available bacterial antagonist of E. amylovora (BlightBan, Pseudomonas fluorescens A506) can be included in antibiotic spray programs. Integration of bacterial antagonists with chemical methods suppresses populations of the pathogen and concomitantly, fills the ecological niche provided by the stigma with a nonpathogenic, competing microorganism. Further integration of biologically based methods with conventional management of blossom blight may be achievable by increasing the diversity of applied antagonists, by refining predictive models to incorporate antagonist use, and by gaining an improved understanding of the interactions that occur among indigenous and applied bacterial epiphytes, antibiotics, and the physical environment.

Fluorescence in situ hybridization (FISH) is a powerful tool for physical mapping in human and other mammalian species. However, application of the FISH technique has been limited in plant species, especially for mapping single- or low-copy DNA sequences, due to inconsistent signal production in plant chromosome preparations. Here we demonstrate that bacterial artificial chromosome (BAC) clones can be mapped readily on rice (Oryza sativa L.) chromosomes by FISH. Repetitive DNA sequences in BAC clones can be suppressed efficiently by using rice genomic DNA as a competitor in the hybridization mixture. BAC clones as small as 40 kb were successfully mapped. To demonstrate the application of the FISH technique in physical mapping of plant genomes, both anonymous BAC clones and clones closely linked to a rice bacterial blight-resistance locus, Xa21, were chosen for analysis. The physical location of Xa21 and the relationships among the linked clones were established, thus demonstrating the utility of FISH in plant genome analysis.

Plant defense responses to pathogen infection involve the production of active oxygen species, including hydrogen peroxide (H2O2). We obtained transgenic potato plants expressing a fungal gene encoding glucose oxidase, which generates H2O2 when glucose is oxidized. H2O2 levels were elevated in both leaf and tuber tissues of these plants. Transgenic potato tubers exhibited strong resistance to a bacterial soft rot disease caused by Erwinia carotovora subsp carotovora, and disease resistance was sustained under both aerobic and anaerobic conditions of bacterial infection. This resistance to soft rot was apparently mediated by elevated levels of H2O2, because the resistance could be counteracted by exogenously added H2O2-degrading catalase. The transgenic plants with increased levels of H2O2 also exhibited enhanced resistance to potato late blight caused by Phytophthora infestans. The development of lesions resulting from infection by P. infestans was significantly delayed in leaves of these plants. Thus, the expression of an active oxygen species-generating enzyme in transgenic plants represents a novel approach for engineering broad-spectrum disease resistance in plants

Transgenic potato and tobacco plants carrying the osmotin gene under the control of the cauliflower mosaic virus 35S promoter constitutively overexpressed osmotin to a level of approximately 2% of total cellular protein. Leaves of transgenic potato plants exhibited delayed development of disease symptoms after inoculation with spore suspensions of Phytophthora infestans, which is the cause of late blight disease of potato. In contrast, transgenic tobacco plants did not display any change in the development of disease symptoms when challenged with either spore suspensions or fungal mycelia of Phytophthora parasitica var. nicotianae. Using in vitro assays, purified osmotin was found to be more effective against P. infestans. Some inhibition of P. parasitica also was observed in vitro even though no in vivo effect could be established

The oomycete Phytophthora infestans Mont. (de Bary), which causes potato late blight, and Potato Virus Y (PVY) are economically important potato pathogens. More virulent P. infestans strains have evolved and are able to overcome resistance genes introgressed earlier to cultivated potato from wild Solanum species, especially from S. demissim Lindl. Potato cultivars resistant to the previously common type of PVY sup(N) may be susceptible to the more virulent isolates of PVY. In previous research, S. guerreroense Corr. (grr) and S. neoantipoviczii Buk. (nan) accessions were rated as resistant to P. infestans and to two (grr) and three (nan) strains of PVY. These parental accessions and their respective hybrid offspring were screened using polymerase chain reaction (PCR) tests to detect alleles conferring resistance to P. infestans (R1 and R3) and to PVY (R sub(Ysto)). Screenings were made in detached leaflet tests (P. infestans), and with the aid of ELISA tests (PVY). The resistance of two hybrids derived from grr was rated as high, mostly due to a hypersensitivity reaction. The allele R3 was detected in only one grr plant among 20 plant populations for each grr and nan accession. R1 and R3 alleles were more frequently detected in one hybrid of grr (grr × B.d.R5.). The resistance allele R sub(Ysto) was found in nan and provided host plant resistance to three strains of PVY, including PVY sup(NTN). Hybrids derived from this accession were characterised by a high frequency of plants bearing the resistant allele R sub(Ysto). In the parental clone tbr × phu, as well as in grr and its hybrids, only the susceptible allele at R sub(Ysto) locus was detected.

Reduced accumulation of the GTP-binding protein Gialpha subunit CPG-1, due either to hypovirus infection or transgenic cosuppression, correlates with virulence attenuation of the chestnut blight fungus, Cryphonectria parasitica. The role of G protein-mediated signal transduction in fungal virulence was further examined by targeted disruption of the gene cpg-1, encoding CPG-1, and a second Galpha gene, cpg-2, encoding the subunit CPG-2. Disruption of cpg-1 resulted in a set of phenotypic changes similar to, but more severe than, those associated with hypovirus infection. Changes included a marked reduction in fungal growth rate and loss of virulence, asexual sporulation, female fertility, and transcriptional induction of the gene lac-1, encoding the enzyme laccase. In contrast, cpg-2 disruption resulted in only slight reductions in growth rate and asexual sporulation and no significant reduction in virulence, female fertility, or lac-1 mRNA inducibility. These results provide definitive confirmation of previous correlative evidence that suggested a requirement of CPG-1-linked signaling for a number of fungal processes, including virulence and reproduction, while demonstrating that a second Galpha, CPG-2, is dispensable for these processes. They also significantly strengthen support for the apparent linkage between hypovirus-mediated disruption of G protein signal transduction and attenuation of fungal virulence

gamma-Aminobutyrate transaminase (GABA-T) catalyzes the conversion of GABA to succinic semialdehyde. Using differential display PCR and cDNA library screening, a full-length GABA-T cDNA (OsGABA-T) was isolated from rice (Oryza sativa) leaves infected with an incompatible race of Magnaporthe grisea. The deduced amino acid sequence comprises 483 amino acid residues and shares 85-69% identity with GABA-T sequences from other plants. OsGABA-T expression is induced by blast fungus infection, mechanical wounding and ultraviolet radiation in rice leaves and is not detected in normal rice organs. This gene is also induced by defense signal molecules such as salicylic acid and abscisic acid, but not by jasmonic acid. Our data suggest that OsGABA-T (GABA shunt) may play a role in restricting the levels of cell death during the host-pathogen interaction.