Biology,Epidemiology and Management of Rhizoctonia solani on Potato

Black scurf and stem canker on potato is an economically important disease complex, causing both quantitative and qualitative damage to potato crops which occurs in potato production areas throughout the world. The ribosomal DNA internal transcribed spacer sequence analysis is currently accepted and a commonly used method for classifying Rhizoctonia species and anastomosis groups (AGs). To date, 13 AGs have been recognized. The updated AG distribution in potato worldwide production areas confirm the status of AG‐3 as the most prevalent AG in potato and reflects the population dynamics of the pathogen probably due to global trading of tubers. As R. solani is a tuber‐ and soilborne pathogen, the ability to detect its levels in the seed tubers and in the soil and predict the potential damage is an important factor in controlling the disease. Effective disease management of Rhizoctonia disease requires implementation of an integrated disease management approach and knowledge of each of its stages. Although the most important control measures are cultural, chemical control (either by seed tuber‐ or in‐furrow treatments) is still an important tool in reducing the damages caused by R. solani.     

Bioactivity of secondary metabolites and thallus extracts from lichen fungi

Fungal secondary compounds and total extracts are known to affect growth of bacteria, fungi, and plants. This study tested the effects of purified compounds and total extracts from three lichens on the growth of two plant pathogens, Ophiostoma novo-ulmi ssp. americana and Sclerotinia sclerotiorum. Usnic acid showed no reduction in relative growth rates (RGR), whereas vulpinic acid reduced RGR for both fungi and atranorin reduced RGR of S. sclerotiorum only. However, purified vulpinic acid showed stronger effects than total extracts on fungal growth. The results suggest that these lichens show further promise as a source for bioactive compounds against fungi.     

1-Tetradecanol, a new alcohol found in the cell wall of some rapidly growing chromogenic mycobacteria

Abstract Three oligosporogenic mutants of Bacillus thuringiensis serovar. israelensis which continue to produce the toxic parasporal body were isolated. The mutants were blocked late in sporulation and were approximately as toxic to mosquito larvae as were the parental strains.     

Callose Synthase in Pinus sylvestris Response during Infection by Species of Heterobasidion annosum sensu lato with Varied Host Preferences

Strengthening of plant cell walls at the site of fungal entry is one of the earliest plant responses to fungal pathogens. The aim of our study was to characterize the pattern of callose synthase localization and callose deposition in roots of Pinus sylvestris after infection by species of the Heterobasidion annosum s.l. complex with different host specificity: H. annosum s.s., H. parviporum and H. abietinum. To address this, sense‐labelled probes and ribonuclease‐treated samples were used to determine in situ hybridizations of callose synthase by FISH method. Furthermore, determination of callose accumulation within P. sylvestris cells was carried out using aniline blue. The different species of H. annosum s.l. had distinct impacts on the callose synthase staining within plant tissues. Moreover, while inoculation with strains of H. abietinum resulted in callose synthase accumulation at the point of hyphae contact with the host cell, this was not observed with the other species. A significant difference in callose synthesis localization was observed after inoculation with varied species of H. annosum s.l. as a result of the specific interactions with the host.     

Construction and operation of a multiplexed microfiltration device to facilitate rapid pathogen detection

Millions of Americans contract food poisoning or are affected by microbial pathogens each year. Rapid, sensitive detection of dilute levels of pathogens in foods, produce, water, and biomanufacturing process samples is key to consumer protection; however, current enrichment methods require as much as a full day to enrich viable bacterial pathogens to detectable levels. Our lab previously demonstrated the ability to concentrate and detect dilute levels of pathogens, within 8 hr, from various food matrices using microfiltration in our continuous cell concentration device (i.e., C3D) with one or two filter modules. This short communication describes the design, materials and construction, layout, and operational characteristics of a four filter module multiplexed system based on a four channel device. Benefits are a 2× greater sample capacity than an equivalent duplex system (achieving the same time to result of less than 8 hr from sample preparation to detection), simpler operation, and a footprint enabling operation inside a biosafety cabinet instead of requiring a BSL-2 room. Flow rate variability through four channels fit within an operational envelope of ±3%; flow rates are reproducible from one run to the next thus ensuring relatively simple, concurrent processing of samples.     

Novel insights into the emergence of pathogens: the case of chestnut blight

Exotic, invasive pathogens have emerged repeatedly and continue to emerge to threaten the world’s forests. Ecosystem structure and function can be permanently changed when keystone tree species such as the American chestnut (Castanea dentata) are eliminated from a whole range by disease. The fungal ascomycete pathogen Cryphonectria parasitica is responsible for causing chestnut blight. Once the pathogen was introduced into the Eastern US, where chestnuts were predominant, chestnuts were all but eliminated. This pathogen is currently causing extensive damage in Europe. A study in this issue of Molecular Ecology sheds new light on the pattern and process of emergence of this devastating plant pathogen ( Dutech et al. 2012 ). The authors used microsatellite markers to investigate the evolutionary history of C. parasitica populations introduced into North America and Europe. To infer sources of migrants and the migration events, the authors included putative source populations endemic to China and Japan, inferred potentially unsampled populations and conducted a multivariate population genetic and complex ABC analysis. Cryphonectria parasitica emerges as an example of an introduced pathogen with limited genotypic diversity and some admixture in the invaded ranges, yet repeated invasions into different areas of Europe and the United States. This work sheds new light on the emergence of C. parasitica providing compelling evidence that this pathogen emerged by repeated migration and occasional admixture.     

Infección por Saccharomyces cerevisiae

BackgroundSaccharomyces cerevisiae is an ubiquitous yeast widely used in industry and it is also a common colonizer of the human mucosae. However, the incidence of invasive infection by these fungi has significantly increased in the last decades.AimsTo evaluate the infection by S. cerevisiae in a hospital in southern Brazil during a period of 10 years (2000-2010).MethodsReview of medical records of patients infected by this fungus.ResultsIn this period, 6 patients were found to be infected by S. cerevisiae. The age range of the patients was from 10 years to 84. Urine, blood, ascitic fluid, peritoneal dialysis fluid, and esophageal biopsy samples were analyzed. The predisposing factors were cancer, transplant, surgical procedures, renal failure, use of venous catheters, mechanical ventilation, hospitalization in Intensive Care Unit, diabetes mellitus, chemotherapy, corticosteroid use, and parenteral nutrition. Amphotericin B and fluconazole were the treatments of choice. Three of the patients died and the other 3 were discharged from hospital.ConclusionsWe must take special precautions in emerging infections, especially when there are predisposing conditions such as immunosuppression or patients with serious illnesses. The rapid and specific diagnosis of S. cerevisiae infections is important for therapeutic decision. Furthermore, epidemiological and efficacy studies of antifungal agents are necessary for a better therapeutic approach.     

Pseudomonas caspiana sp. nov., a citrus pathogen in the Pseudomonas syringae phylogenetic group

In a screening by multilocus sequence analysis of Pseudomonas strains isolated from diverse origins, 4 phylogenetically closely related strains (FBF58, FBF102^T, FBF103, and FBF122) formed a well-defined cluster in the Pseudomonas syringae phylogenetic group. The strains were isolated from citrus orchards in northern Iran with disease symptoms in the leaves and stems and its pathogenicity against citrus plants was demonstrated. The whole genome of the type strain of the proposed new species (FBF102^T = CECT 9164^T = CCUG 69273^T) was sequenced and characterized. Comparative genomics with the 14 known Pseudomonas species type strains of the P. syringae phylogenetic group demonstrated that this strain belonged to a new genomic species, different from the species described thus far. Genome analysis detected genes predicted to be involved in pathogenesis, such as an atypical type 3 secretion system and two type 6 secretion systems, together with effectors and virulence factors. A polyphasic taxonomic characterization demonstrated that the 4 plant pathogenic strains represented a new species, for which the name Pseudomonas caspiana sp. nov. is proposed.     

The genus Dietzia: a new home for some known and emerging opportunist pathogens

The genus Dietzia has only been established fairly recently. The Gram morphology and colony appearance of the species of this genus is remarkably similar to Rhodococcus equi . In the absence of simple, accurate methods for their identification, Dietzia spp. might have been misidentified as a Rhodococcus spp. and/or considered to be contaminants only. This MiniReview is designed to summarize current evidence on the clinical significance of Dietzia species, to consider their potential role as human pathogens, and to outline approaches that can be used to accurately classify and identify members of the genus, with the overall aim of alerting the medical microbiological community to a little known genus that contains clinically significant organisms.     

Mixed PGPR consortium: an effective modulator of antioxidant network for management of collar rot in cauliflower

Abstract

Sclerotinia sclerotiorum is a cosmopolitan fungal pathogen causing stem and collar watery soft rot of cauliflower. Previous management of this disease with chemical pesticides caused hazardous results which lead to use of more eco-friendly microbial approaches. In the present study, consortia of Trichoderma harzianum TNHU27 and Pseudomonas aeruginosa PJHU15 were assessed for their ability in controlling Sclerotinia rot in cauliflower. The seedlings of cauliflower were challenged singly and in consortium with these two compatible microbes. The plants were evaluated upon challenge inoculation with S. sclerotiorum for changes in total phenolic content, the activity of defense and antioxidative enzymes. The microbial consortium comprising of T. harzianum and P. aeruginosa significantly enhanced the defense responses of the plant in comparison to pathogen challenged and unchallenged control. The study elucidates that plant beneficial microbes in the consortium may provide superior protection by induction of faster and enhanced defense responses in comparison to unchallenged and single microbe challenged plants under pathogen challenged conditions.     

Pathogen Sources Estimation and Scenario Analysis Using the Soil and Water Assessment Tool (SWAT)

Concerns over water quality in Ireland have increased in recent years, in part due to the more frequent contamination of drinking water by pathogens such as Escherichia coli and Cryptosporidium. The objective of this study was to assess the use of SWAT for pathogen source estimation and to analyze the effects of various source scenarios on pathogen outputs in Irish catchments. Two agricultural catchments in Ireland susceptible to pathogen contamination of source water were the center of the SWAT model development with the primary focus on levels of E. coli in surface water. Model simulations used site and source specific information which was analyzed considering the total E. coli count for the simulation period (Fergus: January 2005–October 2006; Kilshanvey: January 2006–July 2007). Pathogen source estimation identified point sources as the most significant contributors to E. coli output with direct deposition the primary contributor (95%) in Kilshanvey and wastewater treatment plant outflow (89%) the main contributor in the Fergus catchment. A scenario analysis evaluated possible situations that may occur in study locations. The analysis indicated that restriction of livestock access to water sources and improved wastewater treatment would represent effective methods of improving water quality in both catchments.     

Infection of tobacco with different Pseudomonas syringae pathovars leads to distinct morphotypes of programmed cell death

Tobacco plants (Nicotiana tabacum cv. Xanthi-nc) infiltrated with either of two pathovars of Pseudomonas syringae- an avirulent strain of P. syringae pv. tabaci (Pst) or the non-host pathogen P. syringae pv. maculicola M2 (Psm) - developed a hypersensitive response (HR). There were considerable differences in HR phenotype, timing and sequence of cell dismantling between the two pathosystems. Following Psm infiltration, the first macroscopic signs were visible at 4.5 h post-infiltration (hpi). Simultaneously, increased plasma membrane permeability was observed, suggesting that the loss of cell membrane integrity initiates the macroscopic HR evoked by Psm. In contrast, after Pst treatment there was a distinct time lapse between the first signs of tissue collapse (9 hpi) and the occurrence of plasma membrane discontinuity (12 hpi). Ultrastructural studies of cells undergoing the HR triggered by Psm and Pst revealed distinct patterns of alterations in morphology of organelles. Moreover, while different forms of nuclear degeneration were observed in leaf zones infiltrated with Pst, we failed to detect any abnormalities in the nuclei of Psm-treated tissue. In addition, application of synthetic caspase inhibitors (Ac-DEVD-CHO, Ac-YVAD-CMK) abolished HR induced by Pst, but not Psm. Our observations suggest that different cell death mechanisms are executed in response to Psm and Pst. Interestingly, pre-inoculation with Pst, but not with Psm, induced a long-distance acquired resistance (LDAR) response, even though locally a typical set of defense responses, including acquired resistance, was activated locally in response to Psm. The failure of Psm to induce LDAR may be due to the rapid degeneration of bundle sheath cells resulting from Psm infection.     

Presence of SopE and mode of infection result in increased Salmonella‐containing vacuole damage and cytosolic release during host cell infection by Salmonella enterica

Salmonella enterica serovar Typhimurium (STM) is an invasive, facultative intracellular pathogen that has evolved sophisticated molecular mechanisms to establish an intracellular niche within a specialised vesicular compartment, the Salmonella‐containing vacuole (SCV). The loss of the SCV and release of STM into the cytosol of infected host cells was observed, and a bimodal intracellular lifestyle of STM in the SCV versus life in the cytosol is currently discussed. We set out to investigate the parameters affecting SCV integrity and cytosolic release. A fluorescent protein‐based cytosolic reporter approach was established to quantify, time‐resolved, and on a single cell level, the release of STM into the cytosol of host cells. We observed that the extent of SCV damage and cytosolic release is highly dependent on experimental conditions such as multiplicity of infection, type of host cell line, and STM strain background. Trigger invasion mediated by the Salmonella Pathogenicity Island 1‐encoded type III secretion system (SPI1‐T3SS) and its effector proteins promoted cytosolic release, whereas cytosolic bacteria were rarely observed if entry was mediated by zipper invasion. Presence of SPI1‐T3SS effector SopE was identified as major factor for damage of the SCV in the early phase after STM invasion and sopE‐expressing strains showed higher levels of cytosolic release.     

植物响应病原菌胁迫的蛋白质组学研究进展

随着拟南芥、水稻等模式植物基因组测序的完成,植物基因组学的研究重点已经转变为功能基因组学研究。蛋白质组学成为后基因组时代的重要研究手段,它有助于从分子水平上了解植物功能。主要介绍了双向电泳技术、生物质谱、蛋白质质谱数据的生物信息学分析等蛋白质组学研究的主要技术手段及植物应答病原菌胁迫的蛋白质组学研究进展,并对蛋白质组学在研究植物抗病机制方面的应用前景做出展望。     

酸碱微环境对三种黄瓜主要真菌病原菌的影响

以引起黄瓜灰霉病(Botrytis cinerea)、黑星病(Cladosporium cucumerium)、霜霉病(Pseudoperonospora cubensis)的3种真菌病害病原菌为代表,通过对病菌栖息微环境酸碱度的调节,达到控制病害的目的。研究看出,黄瓜的3种主要病害病原菌在p H=3.4～10 .4间孢子萌发和致病力表现基本一致:偏酸性环境(p H=4 .2～6 .2 )促进孢子萌发率和致病力增强而偏碱性环境(p H=7.5～10 .4 )则对其明显抑制;降低叶面微环境的酸度,大大减轻了病害的发生、扩展,特别是对黄瓜灰霉病菌的防治有明显效果