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Shaonpius Mondal, Yu-Hsuan Lin, Juliet E Carroll, Erik J Wenninger, Nilsa A Bosque-Pérez, Jonathan L Whitworth, Pamela Hutchinson, Sanford Eigenbrode, Stewart M Gray
There has been a recent shift in the prevalence of Potato virus Y (PVY) strains affecting potato with the ordinary strain PVY(O) declining and the recombinant strains PVY(NTN) and PVY(N:O) emerging in the United States. Multiple PVY strains are commonly found in potato fields and even in individual plants. Factors contributing to the emergence of the recombinant strains are not well defined but differential aphid transmission of strains from single and mixed infections may play a role. We found that the transmission efficiencies by Myzus persicae, the green peach aphid, of PVY(NTN), PVY(N:O), and PVY(O) varied depending on the potato cultivar serving as the virus source...
February 10, 2017: Phytopathology
Simona Florea, Daniel G Panaccione, Christopher Lewis Schardl
Ergot alkaloids are highly diverse in structure, exhibit diverse effects on animals, and are produced by diverse fungi in phylum Ascomycota, including pathogens and mutualistic symbionts of plants. These mycotoxins are best known from the fungal family, Clavicipitaceae, and are named for the ergot fungi that, through millennia, have contaminated grains and caused mass poisonings, with effects ranging from dry gangrene to convulsions and death. However, they are also useful sources of pharmaceuticals for a variety of medical purposes...
February 7, 2017: Phytopathology
Shiela Marie Gines Selisana, Mary Jeanie Yanoria, Berlaine Quime, Chaivarakun Chaipanya, Guodong Lu, Rina Bagsic Opulencia, Guo-Liang Wang, Thomas Mitchell, James C Correll, Nick Talbot, Hei Leung, Bo Zhou
Avirulence genes in Magnaporthe oryzae, the fungal pathogen that causes the devastating rice blast disease, have been documented to be major targets subject to mutations to avoid recognition by resistance (R) genes. In this study, an avirulence (AVR) gene-based diagnosis tool for determining the virulence spectrum of a rice blast pathogen population was developed and validated. A set of 77 single-spore field isolates was subjected to pathotype analysis using differential lines each containing a single R gene and classified into 20 virulent pathotypes except for four isolates that lost pathogenicity...
February 7, 2017: Phytopathology
Vicken Hillis, Mark Lubell, Jonathan Kaplan, Kendra Baumgartner
Preventative disease management is challenging to farmers because it requires paying immediate costs in the hopes of returning uncertain future benefits. Understanding farmer decision making about prevention has the potential to reduce disease incidence and minimize the need for more costly post-infection practices. For example, the grapevine trunk-disease complex (Esca, Botryosphaeria dieback, Eutypa dieback, Phomopsis dieback) significantly impacts vineyard productivity and longevity. Given the chronic nature of the infections and inability to eradicate the fungal pathogens, the preventative practices of delayed pruning, applications of pruning-wound protectants, and double pruning (a...
February 7, 2017: Phytopathology
Lucky Kumar Mehra, Christina Cowger, Peter Ojiambo
Stagonospora nodorum blotch (SNB) caused by Parastagonospora nodorum is a serious disease of wheat worldwide. In the United States, the disease is prevalent on winter wheat in many eastern states, and its management relies mainly on fungicide application after flag leaf emergence. Although SNB can occur prior to flag leaf emergence, the relationship between the time of disease onset on yield has not been determined. Such a relationship is useful in identifying a threshold to facilitate prediction of disease onset in the field...
February 7, 2017: Phytopathology
Justine Beaulieu, Blain B Ford, Yilmaz Balci
Genetic diversity of two Phytophthora species, P. cinnamomi (102 isolates) and P. plurivora (186), commonly encountered in Maryland nurseries and forests in the Mid-Atlantic United States was characterized using amplified fragment length polymorphism (AFLP). Expected heterozygosity and other indices suggested a lower level of diversity among P. cinnamomi than P. plurivora. Hierarchical clustering showed P. cinnamomi isolates separated into four clusters, and two of the largest clusters were closely related, containing 80% of the isolates...
February 7, 2017: Phytopathology
Elma Carstens, Celeste Linde, Ruhan Slabbert, Andrew Miles, Nerida Donovan, Hong-Ye Li, Ke Zhang, Megan M Dewdney, Jeffrey A Rollins, Chirlei Glienke, Gerhardus Christian Schutte, Paul Fourie, Adele McLeod
The citrus pathogen Phyllosticta citricarpa was first described 117 years ago in Australia, and subsequently from the summer rainfall citrus-growing regions in China, Africa, South America and recently the United States of America (USA). Limited information is available on the pathogen's population structure, mode of reproduction and introduction pathways, which were investigated by genotyping 383 isolates representing 12 populations from South Africa, USA, Australia, China and Brazil. Populations were genotyped using seven published and eight newly developed polymorphic simple sequence repeat (SSR) markers...
January 30, 2017: Phytopathology
Emil Stefańczyk, Sylwester Sobkowiak, Marta Brylińska, Jadwiga Śliwka
This study describes late blight resistance of potato breeding lines resulting from crosses between cv. Sárpo Mira and Rpi-phu1 gene donors. The progeny is investigated for the presence of Rpi-Smira1 and Rpi-phu1 resistance genes. Interestingly, in detached leaflet tests, plants with both R genes withstand the infection of the Phytophthora infestans isolate virulent to each gene separately, either due to interaction of these genes or presence of additional resistance loci. The interaction was studied further in three chosen breeding lines on the transcriptional level...
January 30, 2017: Phytopathology
Janja Lamovšek, Barbara Gerič Stare, Irena Mavrič Pleško, Saša Širca, Gregor Urek
The increased incidence of the crown gall disease caused by Agrobacterium tumefaciens has long been associated with activities of root-knot nematodes, Meloidogyne spp. Pot experiments on tomato were designed to assess plant vitality, nematode reproduction and crown gall incidence in combined infection with Agrobacterium and Meloidogyne on tomato roots. Results suggest that tomato plants infected with pathogenic A. tumefaciens two days before the nematodes show enhanced plant defense against M. ethiopica resulting in lower egg and gall counts on roots 45 and 90 days post inoculation (dpi); no significantly enhanced defense was observed when the plant was inoculated with bacteria and nematodes at the same time...
January 30, 2017: Phytopathology
Renee Rioux, Ben VanRyzin, Jim Kerns
Brachypodium distachyon is a C3 grass that is an attractive model host system for studying pathogenicity of major turfgrass pathogens, due to its genetic similarity to many cool-season turfgrasses. Infection assays with two or more isolates of the casual agents of dollar spot, brown patch, and Microdochium patch resulted in compatible interactions with B. distachyon inbred line Bd 21-3. The symptoms produced by these pathogens on Bd 21-3 closely resembled those observed on the natural turfgrass host, creeping bentgrass, demonstrating that B...
January 30, 2017: Phytopathology
Daniel D M Bassimba, Jose L Mira, Antonio Vicent
Alternaria brown spot (ABS) is a serious fungal disease of mandarin in the Mediterranean Basin. Due to the rigorous fruit quality standards, models for ABS should avoid false negatives. Experiments were conducted with the susceptible cultivars 'Fortune' and 'Nova' inoculated at different temperatures and leaf wetness durations, including interrupted periods. Effects of temperature and time elapsed after inoculation were also studied. Disease incidence data were fitted to generalized additive models and a generic infection model...
January 30, 2017: Phytopathology
T A Koopman, J C Meitz-Hopkins, A E Bester-van der Merwe, K R Tobutt, C Bester, C L Lennox
Venturia inaequalis isolates were collected during the 2012/13 and 2013/14 seasons from the four principal apple growing regions of South Africa, Elgin (n = 114), Koue Bokkeveld (n = 126), Lower Langkloof (n = 92), and Upper Langkloof (n = 103). Sequence analysis of the ribosomal internal transcribed spacer (ITS) gene regions and genotyping with six (2012/13) and seven (2013/14) microsatellite (SSR) markers was conducted. A subset of 12 isolates from the individual ITS haplotype groups were sequenced for the translation elongation factor-1 alpha (TEF1) and the large subunit of the RNA polymerases II (RPB1) gene regions...
January 27, 2017: Phytopathology
D H Farber, C C Mundt
In addition to pathogen propagule dispersal, disease spread requires successful infection of host tissue. In plant disease epidemiology, susceptibility of host tissue is often assumed to be constant. This assumption ignores changes in host phenology due to developmental stage. To examine this assumption, 3-, 4-, and 5-week-old wheat plants were inoculated with equal quantities of urediniospores of Puccinia striiformis f. sp. tritici, the causal agent of wheat stripe rust (WSR). Disease severity on each leaf was assessed and fit by mixed-effect linear model as a function of leaf position and plant age...
January 24, 2017: Phytopathology
Hitendra Kumar Patel, Patrizia Ferrante, Meng Xianfa, Sree Gowrinadh Javvadi, Sujatha Subramoni, Marco Scortichini, Vittorio Venturi
Bacterial canker disease caused by Pseudomonas syringae pv. actinidiae (Psa), an emerging pathogen of kiwifruit plants, has recently brought about major economic losses worldwide. Genetic studies on virulence functions of Psa have not yet been reported and there is little experimental data regarding bacterial genes involved in pathogenesis. In this study, we performed a genetic screen in order to identify transposon mutants altered in the lipolytic activity as it is known that mechanisms of regulation, production and secretion of enzymes often play crucial roles in virulence of plant pathogens...
January 23, 2017: Phytopathology
Paul A Langlois, Jacob Snelling, John Hamilton, Claude Bragard, Ralf Koebnik, Valerie Verdier, Lindsay Triplett, Jochen Blom, Ned Tisserat, Jan Leach
Prevalence of Xanthomonas translucens, which causes cereal leaf streak (CLS) in cereal crops and bacterial wilt in forage and turfgrass species, has increased in many regions in recent years. Because the pathogen is seedborne in economically important cereals, it is a concern for international and interstate germplasm exchange, and thus, reliable and robust protocols for its detection in seed are needed. However, historical confusion surrounding the taxonomy within the species has complicated the development of accurate and reliable diagnostic tools for X...
January 23, 2017: Phytopathology
Denise Caldwell, Bong Suk Kim, Anjali S Iyer-Pascuzzi
Ralstonia solanacearum is the causal agent of bacterial wilt and infects over 200 plant species in 50 families. The soil-borne bacterium is lethal to many Solanaceous species, including tomatoes. Although resistant plants can carry high pathogen loads (between 10(5) and 10(8) CFU/g fresh weight), the disease is best controlled by the use of resistant cultivars, particularly resistant rootstocks. How these plants have latent infections yet maintain resistance is not clear. R. solanacearum first infects the plant through the root system, and thus early root colonization events may be key to understanding resistance...
January 23, 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
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