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Kathryn Susan Braithwaite, Chuong Nguyen Ngo, Barry J Croft
A cercomonad, tentatively named Phytocercomonas venanatans Ngo, Braithwaite and Bass, is confirmed as the cause of the sugarcane disease chlorotic streak. This was achieved by establishing aseptic liquid cultures of the pathogen isolated from internal pieces of sugarcane stalk tissue. Actively motile cultures of the pathogen were inoculated into sugarcane roots, stalks and leaf whorls. Infected plants subsequently developed the characteristic symptoms of chlorotic streak. Infection was confirmed by PCR screening of plant tissues and by reisolation of the pathogen into aseptic culture followed by PCR and microscopic confirmation...
November 20, 2017: Phytopathology
Laurence V Madden, Gareth Hughes, Wanderson Bucker Moraes, Xiangming Xu, William W Turechek
Spatial pattern, an important epidemiological property of plant diseases, can be quantified at different scales using a range of methods. The spatial heterogeneity (or overdispersion) of disease incidence among sampling units is an especially important measure of small-scale pattern. As an alternative to Taylor's power law for the heterogeneity of counts with no upper bound, the binary power law (BPL) was proposed in 1992 as a model to represent the heterogeneity of disease incidence (number of plant units diseased out of n observed in each sampling unit, or the proportion diseased in each sampling unit)...
November 17, 2017: Phytopathology
Pallavi Sharma, Manu P Gangola, Chen Huang, H Randy Kutcher, Seedhabadee Ganeshan, Ravindra N Chibbar
An in vitro spike culture method was optimized to evaluate Fusarium head blight (FHB) resistance in wheat (Triticum aestivum) and used to screen a population of ethyl methane sulfonate treated spike culture-derived variants (SCDV). Of the 134 SCDV evaluated, the disease severity score of 47 of the variants was ≤30%. Single nucleotide polymorphisms (SNP) in the UDP-glucosyltransferase (UGT) genes, TaUGT-2B, TaUGT-3B, and TaUGT-EST, differed between AC Nanda (an FHB-susceptible wheat variety) and Sumai-3 (an FHB-resistant wheat cultivar)...
November 17, 2017: Phytopathology
Mudassir Iqbal, Mukesh Dubey, Kerstin McEwan, Uwe Menzel, Mikael Andersson Franko, Maria Viketoft, Dan Funck Jensen, Magnus Karlsson
Biological control is a promising approach to reduce plant diseases caused by nematodes. We tested the effect of the fungus Clonostachys rosea strain IK726 inoculation on nematode community composition in a naturally nematode infested soil in a pot experiment, and the effect of C. rosea on plant health. The numbers of plant-parasitic nematode genera extracted from soil and plant roots decreased by 40 to 73% when C. rosea was applied, while genera of nonparasitic nematodes were not affected. Soil inoculation of C...
November 17, 2017: Phytopathology
Elizabeth J Cieniewicz, Sarah J Pethybridge, Gregory Loeb, Keith Perry, Marc Fuchs
Limited information is available on the spread of Grapevine red blotch virus (GRBV, genus Grablovirus, family Geminiviridae) in vineyards. To investigate ecological aspects of red blotch disease spread, sticky cards to catch flying insects were placed in 2015 (April to November) and 2016 (March to November) in a vineyard study site in California where disease incidence increased by nearly 20% between 2014 and 2016. Subsets of insect species or taxa were removed from sticky card traps and individual specimens were tested for the presence of GRBV by multiplex polymerase chain reaction...
November 17, 2017: Phytopathology
Jelli Venkatesh, Jeongtak An, Won-Hee Kang, Molly Jahn, Byoung-Cheorl Kang
Pepper mottle virus (PepMoV) is the most common potyvirus infection of pepper plants and causes significant yield losses. The Pvr7 gene from Capsicum chinense PI159236 and the Pvr4 gene from C. annuum CM334 both have been reported to confer dominant resistance to PepMoV. The Pvr7 locus conferring resistance to PepMoV in C. annuum '9093' was previously mapped to chromosome 10. To develop a high-resolution map of the Pvr7 locus in 9093, we constructed an intraspecific F2 mapping population consisting of 916 individuals by crossing PepMoV-resistant C...
November 17, 2017: Phytopathology
Ji-Fan Hsieh, Aaron Chuah, Hardip R Patel, Karanjeet Sandhu, William J Foley, Carsten Külheim
Plants have developed complex defense mechanisms to protect themselves against pathogens. A wide-host range fungus, Austropuccinia psidii (G. Winter) Beenken comb. nov., which has caused severe damage to ecosystems and plantations worldwide, is a major threat to Australian ecosystems dominated by Myrtaceae. In particular, the east coast wetland foundation tree species Melaleuca quinquenervia appears to be variably susceptible to this pathogen. Understanding the molecular basis of host resistance would enable better management of this rust disease...
November 14, 2017: Phytopathology
Bruna Balen Forcelini, Carolina Suguinoshita Rebello, Nan-Yi Wang, Natalia Peres
Quinone-outside inhibitor (QoI) fungicides are used to manage anthracnose of strawberry, caused by Colletotrichum acutatum. However, selection for resistance to QoI fungicides was first reported in 2013 in Florida, and subsequently in strawberry nurseries and production areas across the USA and Canada. C. acutatum resistance to QoIs is associated with the G143A point mutation in the cytochrome b gene. This mutation is known to be associated with field resistance even at high rates of QoIs. In this study, we investigated the relative fitness and competitive ability of QoI-resistant and -sensitive C...
November 14, 2017: Phytopathology
Shunwen Lu, Michael Edwards
The group 1 pathogenesis-related (PR-1) proteins originally identified from plants and their homologues are also found in other eukaryotic kingdoms. Studies on non-plant PR-1-like (PR-1L) proteins have been pursued widely in humans/animals but rarely in filamentous ascomycetes. Here we report the characterization of four PR-1L proteins identified from the ascomycete fungus Fusarium graminearum, the primary cause of Fusarium head blight of wheat and barley. Molecular cloning revealed that the four FgPR-1L proteins are all encoded by small open reading frames (612 to 909 bp) that are often interrupted by introns, in contrast to plant PR-1 genes that lack introns...
November 8, 2017: Phytopathology
Churamani Khanal, Edward C McGawley, Charles Overstreet, Sally Stetina
The reniform nematode (Rotylenchulus reniformis Linford and Oliveira) has emerged as the most important plant parasitic nematode of cotton in the United States cotton belt. Success in the development of reniform nematode resistant upland cotton cultivars (Gossypium hirsutum L.) has not been realized despite over three decades of breeding efforts. Research approaches ranging from conventional breeding to triple species hybrids to marker-assisted selection have been employed to introgress reniform nematode resistance from other species of cotton into upland cultivars...
November 8, 2017: Phytopathology
Aravind Ravindran, Panatda Saenkham, Julien Gad Levy, Cecilia Tamborindeguy, Hong Lin, Dennis Gross, Elizabeth Ann Pierson
The non-culturable bacterium 'Candidatus Liberibacter solanacearum' (Lso) is the causative agent of zebra chip disease in potato. Computational analysis of the Lso genome revealed a serralysin-like gene based on conserved domains characteristic of genes encoding metalloprotease enzymes similar to serralysin. Serralysin and other serralysin family metalloprotease are typically characterized as virulence factors and are secreted by the type I secretion system (T1SS). The Lso serralysin-like gene is located next to and divergently transcribed from genes encoding a T1SS...
November 6, 2017: Phytopathology
Yariv Ben-Naim, Lidan Falach, Yigal Cohen
Sweet basil (Ocimum basilicum) is susceptible to downy mildew caused by the oomycete foliar pathogen Peronospora belbahrii. No resistant varieties of sweet basil are commercially available. Here, we report on the transfer of resistance gene Pb1 from the highly resistant tetraploid wild basil O. americanum var. americanum (PI 500945, 2n = 4x = 48) to the tetraploid susceptible O. basilicum 'Sweet basil' (2n = 4x = 48). F1 progeny plants derived from the interspecific hybridization PI 500945 × Sweet basil were resistant, indicating that the gene controlling resistance (Pb1) is dominant, but sterile due to the genetic distance between the parents...
October 30, 2017: Phytopathology
Christina Cowger, Lucky Kumar Mehra, Consuelo Arellano, Emily A Meyers, Paul Murphy
Wheat powdery mildew is a disease of international importance that occurs across a wide geographic area in the USA. A virulence survey of Blumeria graminis f. sp. tritici, the causal agent, was conducted by sampling 36 wheat fields in 15 U.S. states in the years 2013 and 2014. Using a hierarchical sampling protocol, isolates were derived from three separated plants at each of five separated sites within each field in order to assess the spatial distribution of pathotypes. A total of 1,017 isolates from those fields were tested individually on single-gene differential cultivars containing a total of 21 powdery mildew resistance (Pm) genes...
October 30, 2017: Phytopathology
Debora Liabeuf, Sung-Chur Sim, David M Francis
Bacterial spot affects tomatoes (Solanum lycopersicum L.) grown under humid conditions. Major genes and quantitative trait loci (QTL) for resistance have been described, and multiple loci from diverse sources need to be combined to improve disease control. We investigated genomic selection (GS) prediction models for resistance to Xanthomonas euvesicatoria and experimentally evaluated the accuracy of these models. The training population consisted of 109 families combining resistance from four sources, and directionally selected from a population of 1,100 individuals...
October 24, 2017: Phytopathology
Yuanye Zhu, Xiaoyu Liang, Yanjun Li, Yabing Duan, Zhitian Zheng, Jianxin Wang, Zhou Mingguo
β-tubulin is the target of benzimidazole fungicides and the most wildly used one of which is Carbendazim (methyl benzimidazol-2-yl-carbamate, MBC). MBC sensitivity is determined by the differential affinity of MBC for β-tubulins. However, the mechanism of less sensitivity of F. graminearum to MBC compared to other fungi including Botrytis cinerea, Colletotrichum gloeosporiodies, and Sclerotinia sclerotiorum remains exclusive. Alignment of β-tubulin acid amino sequences showed that position 240 of β-tubulins is leucine (L) in most pathogenic fungi but is phenylalanine (F) in the Fgβ2-tubulin of F...
October 24, 2017: Phytopathology
W Hao, Timothy D Miles, Frank N Martin, Greg Browne, Helga Forster, James E Adaskaveg
Brown rot of citrus fruits is caused by several species of Phytophthora and is currently of serious concern for the California citrus industry. Two species, P. syringae and P. hibernalis, are quarantine pathogens in China, a major export market for California citrus. To maintain trade and estimate the risk of exporting a quarantine pathogen, the distribution and frequency of Phytophthora species causing brown rot of oranges in major growing areas of California was investigated. Symptomatic fruit were collected from navel (winter to late spring) and Valencia (late spring to summer) orange orchards from 2013 to 2015...
October 20, 2017: Phytopathology
Utsala Shrestha, Mary E Dee, Bonnie H Ownley, David Michael Butler
Growth chamber and field studies were conducted with organic amendment mixtures at C:N ratios 10:1, 20:1, 30:1 and 40:1, and amendment rates 2, 4, 6, and 8 mg C/g soil (C:N ratio 30:1) to evaluate anaerobic soil disinfestation (ASD) effects on germination and colonization of Sclerotium rolfsii. In the growth chamber, sclerotial germination was reduced in all ASD-treatments regardless of C:N ratio (0.6 to 8.5% germination) or amendment rate (7.5 to 46%) as compared to non-amended controls (21 to 36% and 61 to 96%, respectively)...
October 18, 2017: Phytopathology
Stephen Wyka, Cameron McIntire, Cheryl Smith, Isabel Munck, Barret Rock, Heidi Asbjornsen, Kirk Broders
The disease complex white pine needle damage (WPND), first reported in 2006, has now escalated to an epidemic state across the northeastern U.S. Although this complex is composed of several fungal species, Lecanosticta acicola is considered to be the primary causal agent. Knowledge regarding the epidemiology, specific climatic factors that affect the spread of L. acicola on eastern white pine (Pinus strobus) in natural forest settings, and the potential risks repeated defoliation may have on tree health is limited...
October 18, 2017: Phytopathology
Christine L Carroll, Colin A Carter, Rachael E Goodhue, C-Y Cynthia Lin Lawell, Krishna V Subbarao
Plant pathogens migrate to new regions through human activities such as trade, where they may establish themselves and cause disease on agriculturally important crops. Verticillium wilt of lettuce, caused by Verticillium dahliae, is a soilborne fungus that was introduced to coastal California via infested spinach seeds. It has caused significant losses for lettuce growers. Once introduced, Verticillium wilt could be managed by fumigating with methyl bromide and chloropicrin, but this option is no longer available...
October 16, 2017: Phytopathology
Alejandro Ortega-Beltran, Peter Cotty
Aspergillus flavus frequently contaminates maize, a critical staple of billions, with aflatoxins. Diversity among A. flavus L morphotype populations associated with maize in Sonora, Mexico was assessed and a total of 869 isolates from 83 fields were placed into 136 vegetative compatibility groups (VCGs) using nitrate-nonutilizing mutants. VCG diversity indices did not differ in four agroecosystems (AES) but diversity significantly differed among years. Frequencies of certain VCGs changed manyfold over single years in both multiple fields and multiple AES...
October 13, 2017: Phytopathology
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