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Leonardo Pires Boava, Mariângela Cristofani-Yaly, Marcos Antonio Machado
Huanglongbing (HLB) is a destructive disease of citrus caused by phloem-limited bacteria, namely 'Candidatus Liberibacter asiaticus' (Las), 'Candidatus Liberibacter africanus', and 'Candidatus Liberibacter americanus'. Although there are no known HLB-resistant citrus species, studies have reported Poncirus trifoliata as being 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...
March 24, 2017: Phytopathology
Jan C Zadoks
Selected historical pest and disease outbreaks in the Old World are discussed in view of their social and political consequences. Large-scale epidemics always caused social unrest, and often hunger, pestilence and death. When coming on top of deeply rooted and widely spread social unrest such epidemics contributed to political change. Examples are the revolts following epidemics in 1789 and 1846. Epidemics, regardless of causal and target organisms, have elements in common. The notion of a common concept grew into a firmly established discipline: epidemiology...
March 21, 2017: Phytopathology
Nicolas Jelinski, Karen Broz, Wilfried Jonkers, Li-Jun Ma, Harold Corby Kistler
Seventy-four F. oxysporum soil isolates were assayed for known effector genes present in an F. oxysporum f.sp. lycopersici race 3 tomato wilt strain (FOL MN-25) obtained from the same fields in Manatee County, Florida. Based on the presence or absence of these genes, four haplotypes were defined, two of which represented 96% of the surveyed isolates. These two most common effector haplotypes contained either all or none of the assayed race 3 effector genes. We hypothesized that soil isolates with all surveyed effector genes, similar to FOL MN-25, would be pathogenic toward tomato, whereas isolates lacking all effectors would be non-pathogenic...
March 21, 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 soilborne bacterium is lethal to many solanaceous species, including tomato. 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...
March 21, 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 T. 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...
March 20, 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 modeling study, we compared 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...
March 13, 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
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
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
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
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