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Denis Odokonyero, Maria R Mendoza, Peter Moffett, Herman B Scholthof
The objective of this study was to determine the contribution of different ARGONAUTE proteins in Nicotiana benthamiana (NbAGOs) to the defense against silencing sensitive GFP-expressing viral constructs based on Tomato bushy stunt virus (TBSV) (Tombusvirus), Sunn-hemp mosaic virus (Tobamovirus), and Foxtail mosaic virus (Potexvirus). Upon Tobacco rattle virus (TRV)-mediated down-regulation of NbAGO1, 4, 5, or 6, no effects were noted on susceptibility to any virus construct, whereas knockdown of NbAGO2 specifically prevented silencing of P19-defective TBSV (TGdP19)...
June 21, 2017: Phytopathology
Pierre-Antoine Précigout, David Claessen, Corinne Robert
Crop pathogens are known to rapidly adapt to agricultural practices. Although cultivar resistance breakdown and resistance to pesticides have been broadly studied, little is known about the adaptation of crop pathogens to fertilization regimes and no epidemiological model has addressed that question. However, this is a critical issue for developing sustainable low-input agriculture. In this article, we use a model of life history evolution of biotrophic wheat fungal pathogens in order to understand how they could adapt to changes in fertilization practices...
June 21, 2017: Phytopathology
Lichun Yan, Hu Baishi, Gong Chen, Mei Zhao, Ron Ricardo Walcott
Bacterial fruit blotch (BFB), caused by the gram-negative bacterium Acidovorax citrulli, is a serious economic threat to cucurbit crop production worldwide. A. citrulli strains can be divided into two genetically distinct groups with group I strains infecting a range of cucurbit species, and group II strains being predominantly associated with watermelon. Group I and II A. citrulli strains differ in their arsenal of type III secreted (T3S) effector proteins and we hypothesize that these effectors are critical for cucurbit host preference...
June 19, 2017: Phytopathology
Sujan Timilsina, Heather Adkison, Anna Louise Testen, Eric A Newberry, Sally A Miller, Mathews Lal Paret, Gerald V Minsavage, Erica M Goss, Jeffrey B Jones, Gary E Vallad
Recently, in Central Florida tomato production fields, tomato foliage and fruit were observed with symptoms similar to bacterial speck. Fluorescent pseudomonads were consistently isolated and the strains were characterized by standard LOPAT tests, pathogenicity tests and genetic characterization using 16S rRNA sequences and multilocus sequence analysis of conserved housekeeping genes. LOPAT test results indicated the strains were likely P. cichorii. These strains were pathogenic on tomato and were also pathogenic on lettuce, the host for the type strain of P...
June 14, 2017: Phytopathology
Liwei Wen, Charles Bowen, Glen Hartman
Dispersal of urediniospores by wind is the primary means of spread for Phakopsora pachyrhizi, the cause of soybean rust. Our research focused on the short distance transport of urediniospores from movement within and out of the canopy up to 61 m from a source. Environmental variables were used to develop and compare lasso regression, random forest, and neural network models to describe deposition of urediniospores collected in passive and active traps. A random sample consisting of 80% of the data was used for training (referred to as a training dataset) and validating (validation dataset) the models from both types of traps...
June 13, 2017: Phytopathology
Aardra Kachroo, Paul Vincelli, Pradeep Kachroo
Plants have evolved highly specific mechanisms to resist pathogens including preformed barriers and the induction of elaborate signaling pathways. Induced signaling requires recognition of the pathogen either via conserved pathogen-derived factors or specific pathogen-encoded proteins called effectors. Recognition of these factors by host encoded receptor proteins can result in the elicitation of different tiers of resistance at the site of pathogen infection. In addition, plants induce a type of systemic immunity which is effective at the whole plant level and protects against a broad spectrum of pathogens...
June 13, 2017: Phytopathology
Ke Liu, Molli Newman, John A McInroy, Chia-Hui Hu, Joseph W Kloepper
A study was designed to screen individual strains of plant growth-promoting rhizobacteria (PGPR) for broad-spectrum disease suppression in vitro and in planta. In a preliminary screen, 28 of 196 strains inhibited eight different tested pathogens in vitro. In a secondary screen, these 28 strains showed broad spectrum antagonistic activity to six different genera of pathogens, and 24 of the 28 strains produced five traits reported to be related to plant growth promotion, including nitrogen fixation, phosphate solubilization, indole-3-acetic acid production, siderophore production, and biofilm formation...
June 13, 2017: Phytopathology
Guisuibou Daimei, Harpreet Singh Raina, Pushpa Devi Pukhrambam, Gunjan Kumar Saurav, Perumal Renukadevi, Varagur Ganesan Malathi, Chinniah Senthilraja, Bikash Mandal, Rajagopal Raman
The effect of Groundnut bud necrosis virus (GBNV) infection on the life history traits of its vector Thrips palmi and its feeding preference on GBNV-infected plants were studied. A significant difference was observed in the developmental period (1st instar to adult) between the GBNV-infected and healthy thrips, wherein the developmental period of GBNV-infected thrips was decreased. However, there was no effect on the other parameters such as pre-adult mortality, adult longevity and fecundity. Further investigation on settling and feeding choice assay of T...
June 9, 2017: Phytopathology
Yue Lu, Robert Bowden, Guorong Zhang, Xiangyang Xu, Allan Fritz, Guihua Bai
CI13227 is a US winter wheat line with adult-plant slow-rusting resistance that has been the subject of several studies on the characteristics and components of slow-rusting. Previous genetic studies used different populations and approaches and came to different conclusions about the genetic basis of resistance in CI13227. To clarify the situation, a new doubled haploid (DH) population of CI13227 x Lakin was produced and a linkage map was constructed using 5570 single nucleotide polymorphism (SNP) markers derived from wheat 90K SNP assays and 84 simple sequence repeat (SSR) markers...
June 7, 2017: Phytopathology
Katherine Drake-Stowe, Nicolas Bakaher, Simon Goepfert, Berangere Philippon, Regis Mark, Paul D Peterson, Ramsey Lewis
Phytophthora nicotianae and Ralstonia solanacearum are two of the most important pathogens affecting tobacco worldwide. Greater insight on genetic systems controlling resistance to these two soil-borne pathogens, as well as identification of DNA markers associated with genomic regions controlling this resistance, could aid in variety development. An evaluation of 50 historical tobacco lines revealed a high positive correlation between resistances to the two pathogens, preliminarily suggesting that some genomic regions may confer resistance to both pathogens...
June 5, 2017: Phytopathology
Skylar L Fuller, Elizabeth Savory, Alexandra J Weisberg, Jessica Z Buser, Michael I Gordon, Melodie Putnam, Jeff H Chang
Agrobacterium is a genus of soil-borne Gram-negative bacteria. Members carrying oncogenic plasmids can cause crown gall disease, which has significant economic costs, especially for the orchard and nursery industries. Early and rapid detection of pathogenic Agrobacterium is key to the management of crown gall disease. To this end, we designed oligonucleotide primers and probes to target virD2 for use in a molecular diagnostic tool that relies on isothermal amplification and lateral flow-based detection. The oligonucleotide tools were tested in the assay and evaluated for sensitivity, specificity, and breadth in detecting alleles of virD2...
June 1, 2017: Phytopathology
Piero Rinaldi, Donatella Paffetti, Cecilia Comparini, Giovanni Al Broggini, Cesare Gessler, Laura Mugnai
Phyllosticta ampelicida causes black rot disease of Vitis species. Genetic homogeneity of pathogen populations was investigated by analysing the number of haplotypes present in infected samples from Europe and America. The fungus was identified from an analysis of the ITS1-ITS2 region, and partial sequences of β-tubulin and calmodulin genes. The analysis of nuclear microsatellites (nSSR), applied to strains from Vitis species confirmed the existence of a high degree of genetic variability in the fungal populations, revealed four sub-populations and showed that strains from America are distinct from the European ones...
June 1, 2017: Phytopathology
Daniel Teshome Lopisso, Jessica Knüfer, Birger Koopmann, Andreas von Tiedemann
As 'Verticillium stem striping' of oilseed rape (OSR), a vascular disease caused by Verticillium longisporum (VL), is extending into new geographic regions and no control with fungicides exists, the demand for understanding mechanisms of quantitative resistance increases. As VL is strictly limited to the xylem and resistance is expressed in the systemic stage post root invasion, we investigated a potential antifungal role of soluble constituents and nutritional conditions in xylem sap as determinants of cultivar resistance of OSR to VL...
May 31, 2017: Phytopathology
T L Jooste, M Visser, G Cook, J T Burger, H J Maree
The conservation of plant biosecurity relies on the rapid identification of pathogenic organisms, including viruses. With next-generation sequencing (NGS), it is possible to identify multiple viruses within a metagenomic sample. In this study, we explored the use of electronic probes (e-probes) for the simultaneous detection of 11 recognized citrus viruses. E-probes were designed and screened against raw sequencing data to minimize the bioinformatic processing time required. The e-probes were able to accurately detect their cognate viruses in simulated datasets, without any false negatives or positives...
May 30, 2017: Phytopathology
Liming Liu, Bin Peng, Zhenwei Zhang, Yang Wu, Manuel Miras, Miguel A Aranda, Qinsheng Gu
Cucumber green mottle mosaic virus (CGMMV) is a member of the genus Tobamovirus (family Virgaviridae) which causes serious economic losses in cucurbit crops. A possibility for CGMMV control is the use of cross-protection, for which stable attenuated isolates are required. In this study, an infectious clone was constructed for the hn isolate of CGMMV. Unexpectedly, this clone carried a non-conserved mutation involving a single nucleotide change resulting in the replacement of Arg to Cys at residue 284 of the replicase protein; this mutation correlated with delayed symptom induction and RNA accumulation, as shown in time course experiments...
May 25, 2017: Phytopathology
Sara Thomas-Sharma, Jorge Andrade-Piedra, Monica Carvajal Yepes, John Hernandez Nopsa, Michael J Jeger, Roger Jones, Peter Kromann, James P Legg, Jonathan Yuen, Greg Forbes, Karen A Garrett
Pathogen build-up in vegetative planting material, termed seed degeneration, is a major problem in many low-income countries. When smallholder farmers use seed produced on-farm or acquired outside certified programs, it is often infected. We introduce a risk assessment framework for seed degeneration, evaluating the relative performance of individual and combined components of an integrated seed health strategy. The frequency distribution of management performance outcomes was evaluated for models incorporating biological and environmental heterogeneity, with the following results...
May 25, 2017: Phytopathology
Frank Hilker, Linda Allen, Vrushali Bokil, Cheryl Briggs, Zhilan Feng, Karen A Garrett, Louis Gross, Frédéric Hamelin, Michael J Jeger, Carrie Manore, Alison Power, Margaret Redinbaugh, Megan Rúa, Nik J Cunniffe
Maize lethal necrosis (MLN) has emerged as a serious threat to food security in sub-Saharan Africa. MLN is caused by coinfection with two viruses, maize chlorotic mottle virus (MCMV) and a potyvirus, often sugarcane mosaic virus (SCMV). To better understand dynamics of MLN and to provide insight into disease management, we model the spread of the viruses causing MLN within and between growing seasons. The model allows for transmission via vectors, soil and seeds, as well as exogenous sources of infection. Following model parameterisation, we predict how management affects disease prevalence and crop performance over multiple seasons...
May 23, 2017: Phytopathology
Pedro Luis Ramos-González, Camila Chabi-Jesus, Orlene Guerra-Peraza, Aline Daniele Tassi, Elliot Watanabe Kitajima, Ricardo Harakava, Renato Barbosa Salaroli, Juliana Freitas-Astúa
Citrus leprosis (CL) is a viral disease endemic to the Western Hemisphere that produces local necrotic and chlorotic lesions on leaves, branches, and fruit and causes serious yield reduction in citrus orchards. Samples of sweet orange (Citrus × sinensis) trees showing CL symptoms were collected during a survey in noncommercial citrus areas in the southeast region of Brazil in 2013 to 2016. Transmission electron microscopy analyses of foliar lesions confirmed the presence of rod-like viral particles commonly associated with CL in the nucleus and cytoplasm of infected cells...
May 22, 2017: Phytopathology
Zaiton Sapak, Moin U Salam, Elizabeth J Minchinton, Garry P V MacManus, Daryl Joyce, Victor Joseph Galea
A weather-based simulation model, called POMICS, was constructed to predict fungicide application scheduling to manage powdery mildew of cucurbits. The model was developed on the principle that conditions favorable for Podosphaera xanthii, a causal pathogen of this crop disease, generate a number of infection cycles in a single growing season. The model consists of two components that: (i) simulate the disease progression of P. xanthii in secondary infection cycles under natural conditions and (ii) predict the disease severity with application of fungicides at any recurrent disease cycles...
May 18, 2017: Phytopathology
Niklaus J Grünwald, Sydney Everhart, Brian J Knaus, Zhian N Kamvar
Population genetic analysis is a powerful tool to understand how pathogens emerge and adapt. However, determining the genetic structure of populations requires complex knowledge on a range of subtle skills that are often not explicitly stated in book chapters or review articles on population genetics. What is a good sampling strategy? How many isolates should I sample? How do I include positive and negative controls in my molecular assays? What marker system should I use? This review will attempt to address many of these practical questions that are often not readily answered from reading books or reviews on the topic, but emerge from discussions with colleagues and from practical experience...
May 17, 2017: Phytopathology
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