Abstract: In June 2008, Deahl et al. reported the first detection of two isolates of the A2 mating type of Phytophthora infestans on tomato from two locations in Taiwan based on the tests performed at USDA, Beltsville, using A1 and A2 mating types of P. infestans as testers. However, the third and fourth authors of the paper showed that these two isolates (Pi 214 and Pi 566) behaved as A1 mating type when paired with A1 and A2 testers of P. nicotianae (=P. parasitica) at Asian Vegetable Research and Development Center, Shanhua, Taiwan. This information was not included in the report. These two isolates along with two other isolates of P. infestans (Pi 215 and Pi 564) isolated from the same locations on the same dates were re-tested independently in three laboratories using A1 and A2 mating types of P. infestans, P. nicotianae and P. capsici as testers. All four isolates displayed oospore formation when paired with A2 but not A1 mating type regardless of species used as the testers, indicating that all of them are of the A1 mating type. New isolation of P. infestans from diseased tomato plants from the same locations also showed the presence of only the A1 mating type. These results refute the claim by Deahl et al. of the discovery of the A2 mating type of P. infestans from Taiwan.
Abstract: A total of 195 isolates of Phytophthora infestans were collected from late blight-diseased potatoes grown in several localities in the Czech Republic during the years 2007-2008. The isolates were analysed for mating type using the pairing test, CAPS marker assays and PCR assays. Of the 195 tested isolates, 28% were of the A1 mating type and 75% corresponded to the A2 mating type. Furthermore, oospores of P. infestans were microscopically detected in leaf samples from one locality.
Abstract: Root and crown rot (Tristeza disease) is an increasing problem for red pepper crop in La Vera region (Cáceres, western Spain). Field surveys were carried on in 2006 and 2007 to identify the causal agents of this disease. A Phytophthora species was isolated from diseased plants in most of the surveyed fields (27 of 36 in 2006 and 15 of 16 in 2007), while Verticillium spp. were not detected. Fifteen Phytophthora isolates were examined and identified as P. nicotianae, all of them were heterothalic isolates of mating type A2. Pathogenicity tests conducted on 'Jaranda' red pepper plants developed symptoms of wilt and root and crown rot, although disease severity differed significantly (P0.001) among isolates. Results indicate that P. nicotianae is the principal causal agent of the Tristeza disease of red pepper plants in La Vera region and this has several implications for the development of future disease management strategies. The host range of isolates from red pepper plants should be studied in order to establish suitable crop rotation in this region.
Abstract: The Panel on Plant Health was asked to deliver a scientific opinion on the Pest Risk Analysis on Phytophthora ramorum prepared by the FP6 project RAPRA, taking into account comments by Member States and additional information since RAPRA. P. ramorum is the oomycete causing sudden oak death in the USA and leaf and twig blight/dieback on a range of ornamental species in North America and Europe. Currently P. ramorum is not listed as a harmful organism in Council Directive 2000/29/EC, but the Commission adopted in 2002 provisional emergency measures to prevent introduction into and spread within the EU. Recent large-scale outbreaks in Japanese larch (Larix kaempferi) plantations in the UK and Ireland have worsened the potential consequences in the risk assessment area. However, the Panel concludes that the broad narrative in the RAPRA report stands and supports its conclusion that "There is a risk of further entry (of known or new lineages and/or mating types), establishment and [...] impact". It is advisable to avoid introductions of different lineages because of inherent phenotypic differences and the potential for sexual recombination. The Panel supports the management options proposed in the RAPRA report and adds further measures for consideration. Uncertainty remains over the extent to which the association between control measures and gradual reduction in the number of cases in nurseries is causal. The emergency measures have not prevented outbreaks occurring in the natural environment. The many other remaining uncertainties (fitness of progeny, hybridisation with other Phytophthora species, host range and epidemiological role of new hosts, early detection of new outbreaks, understanding of long-range dispersal, structure of plant trade networks, origin of the pathogen) call for further research on P. ramorum across Europe. Regulatory work should keep updated with research results on P. ramorum and further development of the Japanese larch outbreaks.
Abstract: A survey on Phytophthora spp. in the soils and roots of citrus groves was carried out in the main Syrian growing areas of Lattakia and Tartous. Traditional assays (selective medium with soil dilution plates) were used for pathogen detection, and molecular (PCR) assays were used for unanmbiguous identification of P. nicotianae and P. citrophthora in 38.5% of the collected samples. In both locations, P. citrophthora was the predominant species.
Abstract: During the past years there has been an increase in the number of tomato greenhouse facilities in Michoacan. The expected high yield for some of these greenhouses has not been attained due mainly to the presence of tomato diseases, which in many cases, the identity of the pathogen is unknown. The objectives of this research were to determine the incidence and the etiology of the main diseases affecting greenhouse grown tomato in central Michoacan. Sampling was carried out in six commercial tomato greenhouses located in four municipalities from March to October 2007. The main diseases detected were wilting of young and mature plants, late blight, bacterial speck and powdery mildew. The identified pathogens were Phytophthora infestans, Oidiopsis taurica, Rhizoctonia spp., Fusarium oxysporum, Oidium neolycopersici and Pseudomonas syringae pv. tomato. Late blight caused by P. infestans and mildew caused by O. neolycopersici were the most important diseases detected due to the high disease incidence and severity.
Abstract: Traditional culturing methods take a long time for identification of pathogenic isolates. A protocol has been developed for the detection of Fusarium from soil samples in the early stage of infection. Seventeen soil samples from different locations were collected before the onset of rains to find out the presence of Fusarium spp. population present in the soil of guava orchards and to correlate its presence with incidence of wilt. A PCR based method was developed for the molecular characterization of Fusarium using Fusarium spp. specific primer. DNA extracted by this method was free from protein and other contaminations and the yield was sufficient for PCR amplification. The primer developed in this study was amplifying ?230 bp in all infected samples while not in healthy soil. The specificity and sensitivity of primer were tested on several Fusarium spp. and found that this primer was amplifying 10?6 dilution of the fungal DNA. The present study facilitates the rapid detection of Fusarium spp. from infected soil samples of guava collected from different agroclimatic regions in India. A rapid detection method for pathogens and a diagnostic assay for disease would facilitate an early detection of pathogen and lead to more effective control strategies.
Abstract: Phytophthora nicotianae and P. cactorum cause Phytophthora rot of strawberry. A duplex real-time PCR technique for simultaneous detection and quantification of the two pathogens was developed. Species-specific primers for P. nicotianae and P. cactorum were designed based on the internal transcribed spacer regions (ITS) of rDNA and the ras-related protein gene Ypt1, respectively. TaqMan probes were labeled with FAM for P. nicotianae and HEX for P. cactorum. Specificities were demonstrated using 52 isolates, including various soil-borne pathogens. Sensitivities for P. nicotianae and P. cactorum DNAs were 10 fg and 1 pg, respectively. The technique was applied to naturally infested soil and root samples; the two pathogens were detected and the target DNA concentrations were quantified. Significant correlations of DNA quantities in roots and the surrounding soils were found. The minimum soil DNA concentration predicting the development of disease symptoms was estimated as 20 pg (g soil)-1. In three strawberry greenhouses examined, the target DNA concentrations ranged from 1 to 1,655 pg (g soil)-1 for P. nicotianae and from 13 to 233 pg (g soil)-1 for P. cactorum. The method proved fast and reliable, and provides a useful tool to monitor P. nicotianae and P. cactorum in plants or soils.
Abstract: Pyrimorph is a novel fungicide with high activity against the plant pathogen Phytophthora capsici. We investigated the risk that P. capsici can develop resistance to pyrimorph. The baseline sensitivities of 226 P. capsici isolates, tested by mycelial growth inhibition, showed a unimodal distribution with a mean EC50 value of 1.4261 (±0.4002) µg/ml. Twelve pyrimorph-resistant mutants were obtained by repeated exposure to pyrimorph in vitro with a frequency of approximately 1×10-4. The resistance factors of the mutants ranged from 10.67 to 56.02. Pyrimorph resistance of the mutants was stable after 10 transfers on pyrimorph-free medium. Fitness in sporulation, cystospore germination, and pathogenicity in the pyrimorph-resistant mutants was similar to or less than that in the parental wild-type isolates. On detached pepper leaves and pepper plants treated with the recommended maximum dose of pyrimorph, however, virulence was greater for mutants with a high level of pyrimorph resistance than for the wild type. The results suggest that the risk of P. capsici developing resistance to pyrimorph is low to moderate. Among mutants with a high level of pyrimorph resistance, EC50 values for pyrimorph and CAA fungicides flumorph, dimethomorph, and mandipropamid were positively correlated. This indicated that point mutations in cellulose synthase 3 (CesA3) may confer resistance to pyrimorph. Comparison of CesA3 in isolates with a high level of pyrimorph resistance and parental isolates showed that an amino acid change from glutamine to lysine at position 1077 resulted in stable, high resistance in the mutants. Based on the point mutations, an allele-specific PCR method was developed to detect pyrimorph resistance in P. capsici populations.
Abstract: Most Phytophthora spp. are destructive plant pathogens; therefore, effective monitoring and accurate early detection are important means of preventing potential epidemics and outbreaks of diseases. In the current study, a membrane-based oligonucleotide array was developed that can detect Phytophthora spp. reliably using three DNA regions; namely, the internal transcribed spacer (ITS), the 5? end of cytochrome c oxidase 1 gene (cox1), and the intergenic region between cytochrome c oxidase 2 gene (cox2) and cox1 (cox2-1 spacer). Each sequence data set contained ~250 sequences representing 98 described and 15 undescribed species of Phytophthora. The array was validated with 143 pure cultures and 35 field samples. Together, nonrejected oligonucleotides from all three markers have the ability to reliably detect 82 described and 8 undescribed Phytophthora spp., including several quarantine or regulated pathogens such as Phytophthora ramorum. Our results showed that a DNA array containing signature oligonucleotides designed from multiple genomic regions provided robustness and redundancy for the detection and differentiation of closely related taxon groups. This array has the potential to be used as a routine diagnostic tool for Phytophthora spp. from complex environmental samples without the need for extensive growth of cultures.
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