Powdery mildew of tabacco (Erysiphe cichoracearum DC.)

The natural spread of Erysiphe cichoracearum was assessed weekly on alternate leaves of irrigated and non-irrigated tobacco plants of Kutsaga 51 variety, grown in field plots in 1962-63. Leaf area, air temperature and humidity within the plots, relative turgidity of the leaves and soil moisture were also measured. Leaves emerged over a period of 37 days. A minimum of 29 days elapsed between leaf emergence and infection; irrigation lengthened this period by 2–6 days for leaves 2–6 and shortened it by 2–10 days for leaves 10–18. The duration of the initial resistant phase, in leaves at comparable stalk positions, appeared to be directly proportional to the eventual size of the leaves at reaping. Leaves were not infected until they were almost fully expanded. The longest dry period, when most irrigation water was applied, occurred when most lower leaves (2–8) were fully expanded and already infected; upper leaves (10–18)w ere then still expanding and not yet infected. Irrigation increased infection in all leaves; it increased the growth of the pathogen during dry weather and the subsequent susceptibility of leaves that were still actively expanding but not yet infected. Irrigation increased the percentage of susceptible leaf area infected, of intact plants, threefold and that of topped plants ninefold. Topped plants had less infection than intact ones.     

Powdery mildew of tobacco (Erysiphe cichoracearum DC.)

In water culture experiments, tobacco plants of Hicks variety were supplied with factorial combinations of high and low concentrations of nitrogen, phosphorus and potassium. Incidence of powdery mildew and growth and chemical composition of infected and healthy plants were compared.
There was more disease when all elements were supplied at the higher of two concentrations, but the increase in infection was less than the increase in growth. Plants grown in media containing a low ratio of potassium to nitrogen produced the least susceptible leaves; their disease indices were up to 30 times less than those of plants that received the full nutrient treatment. Potassium-deficient leaves had thinner cell walls, larger water content, smaller sugar and potassium contents, and greater amino nitrogen and magnesium contents, compared with those of plants grown in any of the other media. The possible relation between these characteristics and susceptibility to Erysiphe cichoracearum DC. are discussed.     

Development of Perithecia and Reproductive Structures in Two Species of Ceratocystis

Two species of the fungus Ceratocystis are described which havebeen isolated from beetle galleries in Japanese larch. The detaileddevelopment of reproductive structures is described in each,confirming the work of Varitchak in the case of C. piceae. C.autographa is diagnosed as a new heterothallic species.     

Specificity of Interactions Between Wild Lactuca spp. and Bremia lactucae Isolates from Lactuca serriola

Specificity of interactions between eight Lactuca species and 8 Bremia lactucae isolates was studied in seedlings and adult plants of 36 Lactuca accessions plus one L. serriola × L. sativa hybrid. Pathogenicity of the isolates and/or plant susceptibility was expressed by sporulation intensity. A highly compatible relationship was observed in all of L. serriola accession/isolate interactions tested. A differential reaction was found in numerous cases testifying to physiological specialization of the pathogen in a wild pathosystem. Nonspecific nondifferential compatibility (quantitative resistance) can be expected in L. serriola PI 281876. Age dependent resistance (seedlings versus adult plants, and vice versa) and heterogeneity of reactions were also recorded. The comparisonof B. lactucae isolates from L. sativa and L. serriola has shown a significant shift of pathogenicity in favour of L. serriola accessions. A high level of resistance was found in the L. serriola × L. sativa hybrid. The existence of basic incompatibility can be expected in L. saligna and L. virosa as well as in such taxonomically remote species as L. viminea, L. squarrosa and L. biennis. Other taxonomically remote species, i.e. L. dentata and L. alpina, exhibited a compatible reaction, although the reaction of the former was differential. A high level of sporulation was recorded in all accession/isolate interactions of L. alpina.     

Changes in the resistance of tobacco leaf to Erysiphe cichoracearum DC. induced by topping,cytokinins and antibiotics*

Treatments that produced different rates of growth in attached tobacco leaves and leaf discs, also affected the growth of powdery mildew on them. Topping (removal of flower head) increased the resistance of upper leaves, and attached leaves of topped and intact plants were more susceptible than leaf discs from them incubated on water. Hyphal growth increased on leaf discs incubated on water at increasing light intensities, as did dry and fresh mass of healthy discs. On kinetin, dry and fresh mass also increased with light intensity but hyphal growth decreased slightly. Discs incubated at all light intensities on kinetin had less hyphal growth than those on water at the lowest intensity (< 50 lx). Floating leaf discs on chloramphenicol at 500 μ/ml restricted fungal growth but not quite as much as kinetin (10 μ/ml); kinetin inhibited the fungus in the presence of chloramphenicol. Actinomycin D (2.μ5 μ/ml) and puromycin (5.0 μml) had little effect on the fungus.     

Further Investigation of the Specificity of Interactions Between Wild Lactuca spp. and Bremia lactucae Isolates from Lactuca serriola

Callus cultures derived from isogenic lines of the tomato cultivars Moneymaker and Craigella, resistant or susceptible to F. oxysporum f. sp. lycopersici, were inoculated with Fusarium oxysporum f. sp. lycopersici race 1. Fungal growth was restricted on callus derived from resistant plants, after inoculation with a conidial suspension, whereas callus derived from susceptible plants was totally overgrown by the fungus within 7 days. The concentration of the phytoalexin rishitin was significantly higher in the callus culture derived from a resistant tomato line compared with the callus culture from a susceptible line, 2 and 3 days after inoculation with mycelium. The results of the experiments were compared with experiments with whole plants. Rishitin production as well as growth of the fungus was comparable with responses in plant-fungus interaction. Therefore callus culture may be useful in studying the interaction between tomato plants and race 1 of F. oxysporum f. sp. lycopersici.     

Occurrence of Enterococci on Plants in a Wild Environment

Enterococci were obtained from 14% of nearly 2,200 flowers, 3.4% of non-floral structures of angiosperms, and from 8.3% of samples of soil, water, and lesser plants of the Great Smoky Mountains National Park, an area little influenced by the presence of man. The enterococci were recovered from one or more flowers or flower clusters of 1,515 samples in 47 taxa, but not from flowers of 67 taxa with 654 samples. The per cent of recovery was influenced adversely by dense forest cover and by increase in elevation, as compared with recovery from flowers in sunny locations in the lower elevations. The per cent recovery increased directly with rising seasonal temperature, with the maximal per cent of recovery occurring in September. In no instance did all samples of a species of flower or plant yield enterococci on culture, and with only three genera, Cacalia, Delphinium, and Mitchella, were the bacteria obtained from more than 50% of the samples. Approximately 11% of the cultures isolated were identified as Streptococcus faecalis, 64% as the soft curd producing, caseolytic variant of S. faecalis, 4% as S. faecalis var. zymogenes, and 20% as S. faecium. The per cent distribution of these species on plants was reasonably similar to the distribution within wild animals in the same environment. It was concluded that the enterococci occurring on plants arise commonly from the wild animals, and that they do not represent plant-specific species or variants of the enterococci.     

Comparison of Erysiphe cichoracearum and E. cruciferarum and a survey of 360 Arabidopsis thaliana accessions for resistance to these two powdery mildew pathogens

In previous work, UEA1 and UCSC1, two geographically distinct, powdery mildew isolates, were recognized for their ability to infect Arabidopsis thaliana. We have clarified the identity of these isolates by determining their host ranges, reexamining their morphology, and comparing their DNA sequences for the 5.8S ribosomal RNA and two flanking internal transcribed spacer sequences. These experiments confirm that UEA1 is a member of Erysiphe cruciferarum and that UCSC1 belongs to E. cichoracearum. Interactions of the two Erysiphe isolates with 360 A. thaliana accessions were examined to provide a comprehensive profile of naturally occurring powdery mildew resistance in this weedy species. The majority of A. thaliana accessions (213) were susceptible to both isolates. Among the accessions exhibiting some degree of resistance, most (84) responded differentially to UEA1 and UCSC1 and the remainder were resistant to both isolates. Notably, resistance to UCSC1 cosegregated with RPW7, a locus previously demonstrated to confer resistance to UEA1 in Ms-0 x Landsberg (erecta) crosses. With this large collection of resistant accessions, questions about species specificity, genetic diversity and the evolution of resistance to powdery mildews can be addressed.     

Occurrence of Escherichia coli in Wild Cottontail Rabbits

Free-ranging cottontail rabbits (Sylvilagus floridanus) from two areas in central Pennsylvania were sampled over a 4-year period. Large numbers of coliforms were isolated from the intestinal tracts of these animals; in 136 of the 141 rabbits sampled, Escherichia coli was found to be a major component of the alimentary flora. Four serogroups (O7, O77, O73, and O103) were predominant among the isolates and were considered resistant coliflora of this species of cottontail rabbit.     

湖南野生食用菌物种多样性研究

本次报道湖南野生食用菌资源265种,这是近40年来的考察研究结果.这些种类中包括子囊菌10种,担子菌255种,许多种类具有重要的利用和开发意义.对每个种的生态特征和利用价值均进行了简单介绍.     

Occurrence of Escherichia coli in Wild Cottontail Rabbits

[This corrects the article on p. 563 in vol. 33.].     

Constitutive activation of jasmonate signaling in an Arabidopsis mutant correlates with enhanced resistance to Erysiphe cichoracearum,Pseudomonas syringae,and Myzus persicae

In Arabidopsis spp., the jasmonate (JA) response pathway generally is required for defenses against necrotrophic pathogens and chewing insects, while the salicylic acid (SA) response pathway is generally required for specific, resistance (R) gene-mediated defenses against both biotrophic and necrotrophic pathogens. For example, SA-dependent defenses are required for resistance to the biotrophic fungal pathogen Erysiphe cichoracearum UCSC1 and the bacterial pathogen Pseudomonas syringae pv. maculicola, and also are expressed during response to the green peach aphid Myzus persicae. However, recent evidence indicates that the expression of JA-dependent defenses also may confer resistance to E. cichoracearum. To confirm and to extend this observation, we have compared the disease and pest resistance of wild-type Arabidopsis plants with that of the mutants coil, which is insensitive to JA, and cev1, which has constitutive JA signaling. Measurements of the colonization of these plants by E. cichoracearum, P. syringae pv. maculicola, and M. persicae indicated that activation of the JA signal pathway enhanced resistance, and was associated with the activation of JA-dependent defense genes and the suppression of SA-dependent defense genes. We conclude that JA and SA induce alternative defense pathways that can confer resistance to the same pathogens and pests.     

Molecular and Cytogenetic Characterization of Wild Musa Species

The production of bananas is threatened by rapid spreading of various diseases and adverse environmental conditions. The preservation and characterization of banana diversity is essential for the purposes of crop improvement. The world''s largest banana germplasm collection maintained at the Bioversity International Transit Centre (ITC) in Belgium is continuously expanded by new accessions of edible cultivars and wild species. Detailed morphological and molecular characterization of the accessions is necessary for efficient management of the collection and utilization of banana diversity. In this work, nuclear DNA content and genomic distribution of 45S and 5S rDNA were examined in 21 diploid accessions recently added to ITC collection, representing both sections of the genus Musa. 2C DNA content in the section Musa ranged from 1.217 to 1.315 pg. Species belonging to section Callimusa had 2C DNA contents ranging from 1.390 to 1.772 pg. While the number of 45S rDNA loci was conserved in the section Musa, it was highly variable in Callimusa species. 5S rRNA gene clusters were found on two to eight chromosomes per diploid cell. The accessions were genotyped using a set of 19 microsatellite markers to establish their relationships with the remaining accessions held at ITC. Genetic diversity done by SSR genotyping platform was extended by phylogenetic analysis of ITS region. ITS sequence data supported the clustering obtained by SSR analysis for most of the accessions. High level of nucleotide diversity and presence of more than two types of ITS sequences in eight wild diploids pointed to their origin by hybridization of different genotypes. This study significantly expands the number of wild Musa species where nuclear genome size and genomic distribution of rDNA loci is known. SSR genotyping identified Musa species that are closely related to the previously characterized accessions and provided data to aid in their classification. Sequence analysis of ITS region provided further information about evolutionary relationships between individual accessions and suggested that some of analyzed accessions were interspecific hybrids and/or backcross progeny.     

Effects of Weather Variables on Ascospore Discharge from Fusarium graminearum Perithecia

Fusarium graminearum is a predominant component of the Fusarium head blight (FHB) complex of small grain cereals. Ascosporic infection plays a relevant role in the spread of the disease. A 3-year study was conducted on ascospore discharge. To separate the effect of weather on discharge from the effect of weather on the production and maturation of ascospores in perithecia, discharge was quantified with a volumetric spore sampler placed near maize stalk residues bearing perithecia with mature ascospores; the residues therefore served as a continuous source of ascospores. Ascospores were discharged from perithecia on 70% of 154 days. Rain (R) and vapor pressure deficit (VPD) were the variables that most affected ascospore discharge, with 84% of total discharges occurring on days with R≥0.2 mm or VPD≤11 hPa, and with 70% of total ascospore discharge peaks (≥ 30 ascospores/m³ air per day) occurring on days with R≥0.2 mm and VPD≤6.35 hPa. An ROC analysis using these criteria for R and VPD provided True Positive Proportion (TPP) = 0.84 and True Negative Proportion (TNP) = 0.63 for occurrence of ascospore discharge, and TPP = 0.70 and TNP = 0.89 for occurrence of peaks. Globally, 68 ascospores (2.5% of the total ascospores sampled) were trapped on the 17 days when no ascospores were erroneously predicted. When a discharge occurred, the numbers of F. graminearum ascospores sampled were predicted by a multiple regression model with R² = 0.68. This model, which includes average and maximum temperature and VPD as predicting variables, slightly underestimated the real data and especially ascospore peaks. Numbers of ascospores in peaks were best predicted by wetness duration of the previous day, minimum temperature, and VPD, with R² = 0.71. These results will help refine the epidemiological models used as decision aids in FHB management programs.     

国家Ⅱ级重点保护野生植物驼峰藤的研究进展

通过对专著、文献和多个网络资源数据库(植物志、标本、图像等)分析考证,及赴部分产地的野外实地考察,对珍稀濒危植物驼峰藤(Merrillanthus hainanensis Chun et Tsiang)的分类地位、形态特征、标本记录与保存、产地与生境、濒危的野外生存现状等情况进行了综述,以期为该保护物种的生存和发展和保护提供参考。自1933年采集到标本和1941年命名驼峰藤以来,至今已有80多年的历史,研究表明它的分布区范围从原广东、海南省扩展到中国大陆西南部和中南半岛部分地区(缅甸和柬埔寨),部分原有记载分布点已无法找到野生植株,导致其濒危的主要原因是生境的破坏和质量下降,广东中山五桂山脉或许是目前发现的最大野生种群保存地,文中就其保护措施提出了相关建议。     

合肥市野生地被植物种类构成研究

在野外调查和统计分析的基础上,运用五点随机取样法对合肥市的野生地被资源进行了系统的调查,并根据调查结果,选取发生频率大于30%的野生地被植物作为统计分析的对象。运用Spss10.0软件,对综合值采用组间连接法进行聚类分析,找出合肥市不同类型的野生地被植物的常见种类,并分析其发生特点。结果表明:合肥市野生地被植物种类有119种,涉及43科,105属,其中菊科16种,禾本科10种,蓼科9种,十字花科8种。不同类型的野生地被植物种类构成主要有16种:冬春型野生地被植物4种,夏秋型野生地被植物5种,全光照型野生地被植物4种,蜀山森林生态系统型野生地被植物3种。     

Host specificity and virulence variation in populations of lettuce powdery mildew pathogen (Golovinomyces cichoracearum s. str.) from prickly lettuce (Lactuca serriola)

Fifty-four isolates of Golovinomyces cichoracearum (GC) sensu stricto were collected during the period 2008–2010 from natural populations of prickly lettuce (Lactuca serriola) growing in the Czech Republic. Population variation in virulence was assessed with a previously developed race differential set, comprising 13 accessions of four Lactuca species (L. serriola, L. sativa, L. saligna, L. virosa, and L. sativa ‘Hilde’ × L. serriola hybrid). GC isolates differed in their host specificity and virulence; most were able to infect most Lactuca spp. accessions (i.e., complete compatibility), but some showed only moderate virulence (i.e., incomplete compatibility). ‘Avirulent’ reactions were the least common, and these were most frequently observed on L. virosa (LVIR/50) and L. saligna (09-H58-1013). Furthermore, a temporal shift in virulence variability was recorded for the Czech GC populations. Generally, virulence of GC to the Lactuca spp. accessions increased during the study period. Across individual years, the most variable were reactions of GC to L. serriola accession (PI 273617), L. sativa cv. ‘Colorado’, L. saligna (09-H58-1013) and L. virosa (LVIR/50). A broad spectrum of virulence (v)-phenotypes was determined among the 54 isolates; however, differences in the reaction patterns of individual isolates were mostly small and related to differentiation between moderately and completely compatible interactions. However, most of the v-phenotypes characterized were unique to a given population in one year. Altogether, 16 v-phenotypes were identified among 16 isolates tested in 2008, 10 v-phenotypes were determined among 10 isolates tested in 2009, and 24 v-phenotypes among 28 isolates tested in 2010; i.e., different v-phenotypes were identified in different localities.