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J Alejandro Rojas, Janette L Jacobs, Stephanie Napieralski, Behirda Karaj, Carl A Bradley, Thomas Chase, Paul D Esker, Loren J Giesler, Doug J Jardine, Dean K Malvick, Samuel G Markell, Berlin D Nelson, Alison E Robertson, John C Rupe, Damon L Smith, Laura E Sweets, Albert U Tenuta, Kiersten A Wise, Martin I Chilvers
Soybean (Glycine max (L.) Merr.) is produced across a vast swath of North America, with the greatest concentration in the Midwest. Root rot diseases and damping-off are a major concern for production, and the primary causal agents include oomycetes and fungi. In this study, we focused on examination of oomycete species distribution in this soybean production system and how environmental and soil (edaphic) factors correlate with oomycete community composition at early plant growth stages. Using a culture-based approach, 3,418 oomycete isolates were collected from 11 major soybean-producing states and most were identified to genus and species using the internal transcribed spacer region of the ribosomal DNA...
January 18, 2017: Phytopathology
Nian Wang, Lukasz Stelinski, Kirsten Pelz-Stelinski, Jim H Graham, Yunzeng Zhang
The Huanglongbing (HLB) disease pyramid is composed of Liberibacters, psyllid vectors, citrus hosts and the environment. The epidemiological outcomes for Liberibacter-associated plant diseases are collectively determined by the inherent relationships between plant-Liberibacters and psyllids, and how various environment factors affect plant-Liberibacter-psyllid interactions. Citrus-Liberibacter-psyllid interactions occur in a complex microbiome system. In this review, we focus on the progress in understanding the HLB disease pyramid, and how the microbiome affects the HLB disease pyramid including the interaction between HLB and the citrus microbiome; the interaction between Liberibacters and psyllids; the interaction between Liberibacters and gut microbiota in psyllids, and the effect of HLB on selected above- and belowground citrus pathogens...
January 17, 2017: Phytopathology
Sabrina Sarrocco, Fabiola Matarese, Riccardo Baroncelli, Giovanni Vannacci, Verena Seidl-Seiboth, Christian Peter Kubicek, Mariarosaria Vergara
Trichoderma spp. are opportunistic fungi some of which are commonly present in the rhizosphere. Several species, such as Trichoderma virens, are also efficient biocontrol agents against phytopathogenic fungi and exert beneficial effects on plants. These effects are the consequence of interactions between Trichoderma and plant roots, which trigger enhanced plant growth and induce plant resistance. We have previously shown that T. virens I10 expresses two endopolygalacturonase genes, tvpg1 and tvpg2, during the interaction with plant roots; tvpg1 is inducible while tvpg2 is constitutively transcribed...
January 17, 2017: Phytopathology
Marjolein Elisabeth Lof, Claude de Vallavieille-Pope, Wopke van der Werf
Genetic resistance in crops is a cornerstone of disease management in agriculture. Such genetic resistance is often rapidly broken due to selection for virulence in the pathogen population. Here we ask whether there are strategies that can prolong the useful life of plant resistance genes. In a modelling study, we compare four deployment strategies: gene pyramiding, sequential use, simultaneous use, and a mixed strategy. We developed a spatially explicit model for France and parameterized it for the fungal pathogen Puccinia striiformis f...
January 17, 2017: Phytopathology
James Daley, Sandra Branham, Amnon Levi, Richard Hassell, Patrick Wechter
Infection with Alternaria cucumerina causes Alternaria leaf blight (ALB), a disease characterized by lesion formation on leaves, leading to substantial yield and quality losses in Cucumis melo (melon). Although fungicides are effective against ALB, reduction in the frequency of application would be economically and environmentally beneficial. Resistant melon lines have been identified but the genetic basis of this resistance has not been determined. A saturated melon genetic map was constructed with markers developed through genotyping by sequencing of a recombinant inbred line population (F6 to F10; n = 82) derived from single-seed descent of a F2 population from a cross between the ALB-resistant parent MR-1 and the ALB-susceptible parent Ananas Yokneum...
January 17, 2017: Phytopathology
Helvécio D Coletta-Filho, Carolina S Francisco, João R S Lopes, Christiane Muller, Rodrigo P P Almeida
Homologous recombination affects the evolution of bacteria such as Xylella fastidiosa, a naturally competent plant pathogen that requires insect vectors for dispersal. This bacterial species is taxonomically divided into subspecies, with phylogenetic clusters within subspecies that are host specific. One subspecies, pauca, is primarily limited to South America, with the exception of recently reported strains in Europe and Costa Rica. Despite the economic importance of X. fastidiosa subsp. pauca in South America, little is known about its genetic diversity...
January 17, 2017: Phytopathology
Alexey Mikaberidze, Neil Paveley, Sebastian Bonhoeffer, Frank van den Bosch
Resistance to antimicrobial drugs allows pathogens to survive drug treatment. The time taken for a new resistant mutant to reach a population size which is unlikely to die out by chance is called "emergence time". Prolonging emergence time would delay loss of control. We investigate the effect of fungicide dose on the emergence time in fungal plant pathogens. A population dynamical model is combined with dose-response data for Zymoseptoria tritici, an important wheat pathogen. Fungicides suppress sensitive pathogen population...
January 12, 2017: Phytopathology
Leonardo Pires Boava, Mariângela Cristofani-Yaly, Marcos Antonio Machado
Huanglongbing (HLB) is a destructive disease of citrus caused by phloem-limited bacteria, namely, Liberibacter asiaticus (Las) L. africanus (Laf) and L. americanus (Lam). Although there are no known HLB-resistant citrus species, Poncirus trifoliata has been reported as more tolerant. Assuming that callose deposition in the phloem of infected plants can inhibit translocation of photosynthetic products and cause starch accumulation, we compared callose deposition in petioles and starch accumulation in infected leaves of three genotypes (Citrus sinensis, C...
January 9, 2017: Phytopathology
Suzanne Slack, Quan Zeng, Cory Outwater, George W Sundin
Fire blight, caused by the pathogen Erwinia amylovora (Burrill) Winslow et al, is the most devastating bacterial disease of pome fruits in North America and worldwide. The primary method of dispersal for E. amylovora is through ooze, a mass of exopolysaccharides and bacterial cells that is exuded as droplets from infected host tissue. During the 2013 and 2014 field seasons, 317 ooze droplets were collected from field-inoculated apple trees. Populations of E. amylovora in ooze droplets were 108 colony forming units per microliter on average (cfu/µl)...
January 3, 2017: Phytopathology
Anna Thomas, Ignazio Carbone, Yigal Cohen, Peter S Ojiambo
During the past two decades, a resurgence of cucurbit downy mildew has occurred around the world, resulting in severe disease epidemics. In the United States, resurgence of the disease occurred in 2004 and several hypotheses, including introduction of a new genetic recombinant or pathotype of the pathogen, have been suggested as potential causes for this resurgence. Occurrence and distribution of mating types of Pseudoperonospora cubensis in the United States were investigated using 40 isolates collected from cucurbits across 11 states from 2005 to 2013...
January 3, 2017: Phytopathology
Friederike Busse, Annette Bartkiewicz, Diro Terefe-Ayana, Frank Niepold, Yvonne Schleusner, Kerstin Flath, Nicole Sommerfeldt-Impe, Jens Lübeck, Josef Strahwald, Eckhard Tacke, Hans-Reinhard Hofferbert, Marcus Linde, Jarosław Przetakiewicz, Thomas Debener
Synchytrium endobioticum is an obligate biotrophic fungus that causes wart diseases in potato. Like other species of the class Chytridiomycetes, it does not form mycelia and its zoospores are small, approximately 3 μm in diameter, which complicates the detection of early stages of infection. Furthermore, potato wart disease is difficult to control because belowground organs are infected and resting spores of the fungus are extremely durable. Thus, S. endobioticum is classified as a quarantine organism. More than 40 S...
January 3, 2017: Phytopathology
Yamila C Agrofoglio, Verónica C Delfosse, María F Casse, Horacio E Hopp, Iván Bonacic Kresic, Ana J Distéfano
An outbreak of a new disease occurred in cotton (Gossypium hirsutum) fields in northwest Argentina starting in the 2009-10 growing season and is still spreading steadily. The characteristic symptoms of the disease included slight leaf rolling and a bushy phenotype in the upper part of the plant. In this study, we determined the complete nucleotide sequences of two independent virus genomes isolated from cotton blue disease (CBD)-resistant and -susceptible cotton varieties. This virus genome comprised 5,866 nucleotides with an organization similar to that of the genus Polerovirus and was closely related to cotton leafroll dwarf virus, with protein identity ranging from 88 to 98%...
December 30, 2016: Phytopathology
Christopher K Morrison, Tanya Arseneault, Amy Novinscak, Martin Filion
Phytophthora infestans causes late blight of potato, one of the most devastating diseases affecting potato production. Alternative approaches for controlling late blight are being increasingly sought due to increasing environmental concerns over the use of chemical pesticides and the increasing resistance of P. infestans to fungicides. Our research group has isolated a new strain of Pseudomonas fluorescens (LBUM636) of biocontrol interest producing the antibiotic phenazine-1-carboxylic acid (PCA). Wild-type LBUM636 was shown to significantly inhibit the growth of Phytophthora infestans in in vitro confrontational assays whereas its isogenic mutant (phzC-; not producing PCA) only slightly altered the pathogen's growth...
December 30, 2016: Phytopathology
Yu Lei, Meinan Wang, Anmin Wan, Chongjing Xia, Deven R See, Min Zhang, Xianming Chen
Puccinia striiformis causes stripe rust on wheat, barley, and grasses. Natural population studies have indicated that somatic recombination plays a possible role in P. striiformis variation. To determine whether somatic recombination can occur, susceptible wheat or barley plants were inoculated with mixed urediniospores of paired isolates of P. striiformis. Progeny isolates were selected by passing through a series of inoculations of wheat or barley genotypes. Potential recombinant isolates were compared with the parental isolates on the set of 18 wheat or 12 barley genotypes that are used to differentiate races of P...
December 30, 2016: Phytopathology
Benoit Marçais, Dominique Piou, Damien Dezette, Marie-Laure Desprez-Loustau
Coinfection by several pathogens is increasingly recognized as an important feature in the epidemiology and evolution of plant fungal pathogens. Oak mildew is induced by 2 closely related Erysiphe invasive species E. alphitoides and E. quercicola, which differ in their mode of overwintering. We investigated how climate influences the co-occurrence of the 2 species in oak young stands and whether this is important for the disease epidemiology We studied the frequency of flag-shoots (i.e. shoots developing from infected buds, usually associated with E...
December 27, 2016: Phytopathology
Qiongnan Gu, Meijuan Chen, Junbin Huang, Y D Wei, Tom Hsiang, Lu Zheng
The infection process of Colletotrichum higginsianum, which causes a disease of crucifers, involves several key steps: conidial germination, appressorial formation, appressorial penetration, and invasive growth in host tissues. In this study, the ChRgf gene encoding a Ras guanine-nucleotide exchange factor protein was identified by screening T-DNA insertion mutants generated from Agrobacterium tumefaciens-mediated transformation (AtMT) that were unable to cause disease on the host Arabidopsis thaliana. Targeted gene deletion of ChRgf resulted in a null mutant (ΔChrgf-42) with defects in vegetative growth, hyphal morphology and conidiation, and poor surface attachment and low germination on hydrophobic surfaces, but there were no apparent differences in appressorial turgor pressure between the wild-type and the mutant...
December 27, 2016: Phytopathology
Zhiyuan Lǚ, Xin Kang, Zhonghuai Xiang, Ningjia He
Scleromitrula shiraiana causes the popcorn disease in mulberry trees resulting in severe economic losses. Previous studies have shown that melanin may play a vital role in establishing the pathogenicity of fungi. In the present study, we identified the melanin produced in S. shiraiana belongs to DHN melanin by gas chromatography-mass spectrometry, and cloned the laccase Sh-lac, a potential DHN melanin biosynthesis gene from S. shiraiana. We obtained two stable Sh-lac silenced transformants using RNAi, ilac-4 and 8 to elucidate the DHN melanin biosynthetic pathway in S...
December 23, 2016: Phytopathology
J Alejandro Rojas, Janette L Jacobs, Stephanie Napieralski, Behirda Karaj, Carl A Bradley, Thomas Chase, Paul D Esker, Loren J Giesler, Doug J Jardine, Dean K Malvick, Samuel G Markell, Berlin D Nelson, Alison E Robertson, John C Rupe, Damon L Smith, Laura E Sweets, Albert U Tenuta, Kiersten A Wise, Martin I Chilvers
Oomycete pathogens are commonly associated with soybean root rot and have been estimated to reduce soybean yields in the United States by 1.5 million tons on an annual basis. Limited information exists regarding the frequency and diversity of oomycete species across the major soybean-producing regions in North America. A survey was conducted across 11 major soybean-producing states in the United States and the province of Ontario, Canada. In 2011, 2,378 oomycete cultures were isolated from soybean seedling roots on a semiselective medium (CMA-PARPB) and were identified by sequencing of the internal transcribed spacer region of rDNA...
December 23, 2016: Phytopathology
Wayne M Jurick, Otilia Macarisin, Verneta L Gaskins, Eunhee Park, Jiujiang Yu, Wojciech Janisiewicz, Kari A Peter
Botrytis cinerea causes gray mold and is an economically important postharvest pathogen of fruit, vegetables, and ornamentals. Fludioxonil-sensitive B. cinerea isolates were collected in 2011 and 2013 from commercial storage in Pennsylvania. Eight isolates had values for effective concentrations for inhibiting 50% of mycelial growth of 0.0004 to 0.0038 μg/ml for fludioxonil and were dual resistant to pyrimethanil and thiabendazole. Resistance was generated in vitro, following exposure to a sublethal dose of fludioxonil, in seven of eight dual-resistant B...
December 22, 2016: Phytopathology
Maria Cristina Canale, Arthur Fernando Tomaseto, Marineia de Lara Haddad, Helvécio Della Coletta-Filho, João Roberto Spotti Lopes
Although 'Candidatus Liberibacter asiaticus' (Las) is a major pathogen associated with citrus huanglongbing (HLB), some characteristics of transmission by the psyllid vector Diaphorina citri are not fully understood. We examined the latent period and persistence of transmission of Las by D. citri in a series of experiments at 25°C, in which third-instar psyllid nymphs and 1-week-old adults were confined on infected citrus for an acquisition access period (AAP), and submitted to sequential inoculation access periods (IAPs) on healthy citrus seedlings...
December 22, 2016: Phytopathology
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