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H Ramdial, R K Latchoo, F N Hosein, S N Rampersad
Fusarium spp. are ranked among the top 10 most economically and scientifically important plant-pathogenic fungi in the world and are associated with plant diseases that include fruit decay of a number of crops. Fusarium isolates infecting bell pepper in Trinidad were identified based on sequence comparisons of the translation elongation factor gene (EF-1a) with sequences of Fusarium incarnatum-equiseti species complex (FIESC) verified in the FUSARIUM-ID database. Eighty-two isolates were identified as belonging to one of four phylogenetic species within the subclades FIESC-1, FIESC-15, FIESC-16, and FIESC-26, with the majority of isolates belonging to FIESC-15...
November 30, 2016: Phytopathology
Kathleen M Burchhardt, Megan E Miller, William O Cline, Marc A Cubeta
The fungus Monilinia vaccinii-corymbosi, a pathogen of Vaccinium spp., requires asexual and sexual spore production to complete its life cycle. A recent study found population structuring of M. vaccinii-corymbosi over a broad spatial scale in the United States. In this study, we examined fine-scale genetic structuring, temporal dynamics, and reproductive biology within a 125-by-132-m blueberry plot from 2010 to 2012. In total, 395 isolates of M. vaccinii-corymbosi were sampled from infected shoots and fruit to examine their multilocus haplotype (MLH) using microsatellite markers...
November 30, 2016: Phytopathology
E M Babiker, T C Gordon, S Chao, M N Rouse, R Wanyera, M Acevedo, G Brown-Guedira, J M Bonman
Wheat landrace PI 177906 has seedling resistance to stem rust caused by Puccinia graminis f. sp. tritici races TTKSK, TTKST, and BCCBC and field resistance to the Ug99 race group. Parents, 140 recombinant inbred lines, and 138 double haploid (DH) lines were evaluated for seedling resistance to races TTKSK and BCCBC. Parents and the DH population were evaluated for field resistance to Ug99 in Kenya. The 90K wheat single nucleotide polymorphism (SNP) genotyping platform was used to genotype the parents and populations...
November 30, 2016: Phytopathology
R M Beresford, J L Tyson, W R Henshall
A weather-based disease prediction model for bacterial canker of kiwifruit (known worldwide as Psa; Pseudomonas syringae pv. actinidiae biovar 3) was developed using a new mechanistic scheme for bacterial disease forecasters, the multiplication and dispersal concept. Bacterial multiplication is estimated from a temperature function, the M index, accumulated from hourly air temperature over 3 days for hours when the leaf canopy is wet. Rainfall provides free water to move inoculum to infection sites, and the daily risk indicator, the R index, is the 3-day accumulation of the M index output on days with total rainfall >1 mm; otherwise, R is zero...
November 30, 2016: Phytopathology
Karen-Beth G Scholthof
One of the seminal events in plant pathology was the discovery by Francis O. Holmes that necrotic local lesions induced on certain species of Nicotiana following rub-inoculation of Tobacco mosaic virus (TMV) was due to a specific interaction involving a dominant host gene (N). From this, Holmes had an idea that if the N gene from N. glutinosa was introgressed into susceptible tobacco, the greatly reduced titer of TMV would, by extension, prevent subsequent infection of tomato and pepper plants by field workers whose hands were contaminated with TMV from their use of chewing and smoking tobacco...
November 30, 2016: Phytopathology
Mark Mazzola, Shiri Freilich
Biological disease control of soil-borne plant diseases has traditionally employed the biopesticide approach whereby single strains or strain mixtures are introduced into production systems through inundative/inoculative release. The approach has significant barriers that have long been recognized, including a generally limited spectrum of target pathogens for any given biocontrol agent andinadequate colonization of the host rhizosphere, which can plague progress in the utilization of this resource in commercial field-based crop production systems...
November 29, 2016: Phytopathology
Daniel Farber, Chris 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- wk 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...
November 29, 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 GC-MS, 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...
November 21, 2016: Phytopathology
James Daley, Sandra E Branham, Amnon Levi, Richard Hassell, William 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). While 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 an MR-1 (resistant) by Ananas Yokneum (susceptible Israeli cultivar) a recombinant inbred line (RIL) population (F6-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...
November 21, 2016: Phytopathology
Trevor A Koopman, Julia Christine Meitz-Hopkins, Aletta E Bester-van der Merwe, Kenneth R Tobutt, Cecilia Bester, Cheryl 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 (RBP1) gene regions...
November 21, 2016: Phytopathology
Alejandro Rojas, Janette L Jacobs, Stephanie Napieralski, Behirda Karaj, Carl A Bradley, Tom Chase, Paul Esker, Loren Giesler, Douglas Jardine, Dean Malvick, Sam Markell, Berlin D Nelson, Alison Robertson, John C Rupe, Damon Smith, Laura Sweets, Albert Tenuta, Kiersten 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 to oomycete community composition at early plant growth stages. Using a culture-based approach, a total of 3,418 oomycete isolates were collected from 11 major soybean producing states and most were identified to genus and species using the ITS region of the rDNA...
November 14, 2016: Phytopathology
Anna Thomas, Ignazio Carbon, Yigal Cohen, Peter 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 P. cubensis in the United States were investigated using 40 isolates collected from cucurbits across eleven states from 2005 to 2013...
November 14, 2016: Phytopathology
Wayne Michael Jurick Ii, Otilia Macarisin, Verneta L Gaskins, Eunhee Park, Jiujiang Yu, Wojciech Jerzy Janisiewicz, Kari Peter
Botrytis cinerea causes gray mold and is an economically important postharvest pathogen of fruits, vegetables and ornamentals. Fludioxonil sensitive B. cinerea isolates were collected in 2011 and 2013 from commercial storage in Pennsylvania. Eight isolates had EC50 values ranging from 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 sub-lethal dose of fludioxonil, in seven of eight dual-resistant B. cinerea isolates...
November 14, 2016: Phytopathology
Maria Cristina Canale, Arthur Fernando Tomaseto, Marineia de Lara Haddad, Helvécio Della Coletta-Filho, Joao 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 25oC, 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...
November 14, 2016: Phytopathology
Virginia Müller, Gustavo Bonacci, Carlos Batthyany, María Valeria Amé, Fernando Carrari, Jorge Omar Gieco, Ramon Asis
Significant efforts are being made to minimize aflatoxin contamination in peanut seeds and one possible strategy is to understand and exploit the mechanisms of plant defense against fungal infection. In this study we have identified and characterized, at biochemical and molecular levels, plant protease inhibitors (PPIs) produced in peanut seeds of the resistant PI337394 and the susceptible Forman cultivar during A. parasiticus colonization. With chromatographic methods and 2D electrophoresis-mass spectrometry we have isolated and identified four variants of Bowman-Birk trypsin inhibitor (BBTI) and a novel Kunitz-type protease inhibitor (KPI) produced in response to A...
November 14, 2016: Phytopathology
Christina Heber Hagerty, Nicole P Anderson, Chris Mundt
Fungicide resistance can cause disease control failure in agricultural systems, and is particularly concerning with Zymoseptoria tritici, the causal agent of Septoria tritici blotch of wheat. In North America, the first quinone outside inhibitors (QoI) resistance in Z. tritici was discovered in the Willamette Valley of Oregon in 2012, which prompted this hierarchical survey of commercial winter wheat fields to monitor azoxystrobin- and propiconazole-resistant Z. tritici. Surveys were conducted in June 2014, January 2015, May 2015, and January 2016...
November 9, 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 P...
November 9, 2016: Phytopathology
Helvecio Coletta-Filho, Carolina Francisco, Joao Lopes, Christiane Muller, Rodrigo Almeida
Homologous recombination impacts 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...
November 9, 2016: 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 Chytridiomycetes it does not form mycelia and its zoospores are small, approximately 3µm in diameter, which complicate the detection of early stages of infection. Furthermore, potato wart disease is difficult to control as belowground organs are infected and resting spores of the fungus are extremely durable. S. endobioticum is thus classified as a quarantine organism. More than 40 S. endobioticum pathotypes have been reported, of which pathotypes 1(D1), 2(G1), 6(O1), 8(F1) and 18(T1) are the most important in Germany...
November 9, 2016: Phytopathology
S Li, F Bonneu, J Chadoeuf, D Picart, A Gégout-Petit, L Guérin-Dubrana
To assess the capacity of esca to spread within vineyards of the Bordeaux region, over 8 years of annual records, containing between 1,200 and 2,300 contiguous Cabernet Sauvignon vines from 15 mature vineyards, were used for spatial statistical analyses. A group of nonparametric tests, based on join count statistics and on permutation methods, was developed to characterize the spatial structure of esca-symptomatic vines in terms of spread in any direction or within-row only. Among vineyards, a large range of spatial patterns, from random to strongly structured, associated with various prevalence rates that increased over time were observed...
November 7, 2016: Phytopathology
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