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Louisamarie Parkinson, Roger Shivas, Elizabeth Dann
Black root rot is a severe disease of young avocado trees in Australia causing black necrotic roots, tree stunting, and leaf drop prior to tree death. Nectriaceous fungi (Nectriaceae, Hypocreales), are commonly isolated from symptomatic roots. This research tested the pathogenicity of 19 isolates from Calonectria, Cylindrocladiella, Dactylonectria, Gliocladiopsis and Ilyonectria, spp. collected from young avocado trees and other hosts. Glasshouse pathogenicity tests with avocado (Persea americana) cv. Reed seedlings confirmed that Calonectria ilicicola is a severe pathogen of avocado, causing stunting, wilting and seedling death within 5 weeks of inoculation...
July 19, 2017: Phytopathology
Emmanuel M Mgonja, Chan Ho Park, Houxiang Kang, Elias G Balimponya, Stephen Opiyo, Maria Bellizzi, Samuel K Mutiga, Felix Rotich, Veena Devi Ganeshan, Robert Mabagala, Clay Sneller, Jim Correll, Bo Zhou, Nicholas J Talbot, Thomas K Mitchell, Guo-Liang Wang
Understanding the genetic diversity of rice germplasm is important for the sustainable use of genetic materials in rice breeding and production. Africa is rich in rice genetic resources that can be utilized to boost rice productivity on the continent. A major constraint to rice production in Africa is rice blast, caused by the hemibiotrophic fungal pathogen Magnaporthe oryzae. In this report, we present the results of a genotyping-by-sequencing (GBS)-based diversity analysis of 190 African rice cultivars and an association mapping of blast resistance (R) genes and quantitative trait loci (QTLs)...
July 18, 2017: Phytopathology
Anna Maria Szyniszewska, Constantine Busungu, Simon Boniface Boni, Rudolph Rufini Shirima, Hein Bouwmeester, James P Legg
To improve understanding of the dynamics of the cassava mosaic disease (CMD) pandemic front, geospatial approaches were applied to the analysis of three years' data obtained from a 2° by 2° (ca 222km by 222 km) area of north-western Tanzania. A total of 80 farmers' fields were assessed in each of 2009, 2010 and 2011, with 20 evenly-distributed fields per 1° by 1° quadrant. CMD-associated variables (CMD incidence, CMD severity, vector-borne CMD infection and vector abundance) increased in magnitude from 2009-2010, but showed little change from 2010-2011...
July 15, 2017: Phytopathology
Rui Wang, Jianli Chen, James A Anderson, Junli Zhang, Weidong Zhao, Justin Wheeler, Natalie Klassen, Deven R See, Yanhong Dong
Fusarium head blight is a destructive disease of wheat in humid and semi-humid areas of the world. It has emerged in the Pacific Northwest (PNW) in recent years because of changing climate and crop rotation practices. Our objectives in the present study were to identify and characterize QTL associated with FHB resistance in spring wheat lines developed in the PNW and the International Maize and Wheat Improvement Center (CIMMYT). A total of 170 spring wheat lines were evaluated in field and greenhouse trials in 2015 and 2016...
July 13, 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...
July 13, 2017: Phytopathology
Guichun Wu, Panpan Su, Bo Wang, Yuqiang Zhang, Guoliang Qian, Fengquan Liu
Xanthomonas oryzae pv. oryzae, an economically important bacterium, causes a serious disease in rice production worldwide called bacterial leaf blight. How X. oryzae pv. oryzae infects rice and causes symptoms remains incompletely understood. Our earlier works demonstrated that the twin-arginine translocation (Tat) pathway plays an vital role in X. oryzae pv. oryzae fitness and virulence but the underlying mechanism is unknown. In this study, we used strain PXO99(A) as a working model, and identified 15 potential Tat-dependent translocation proteins (TDTP) by using comparative proteomics and bioinformatics analyses...
July 12, 2017: Phytopathology
Paulo Santos Faria Lichtemberg, Yong Luo, Rafael G Morales, Juliana Marta Muehlmann Fischer, Themis J Michailides, Louise Larissa May De Mio
The ascomycete Monilinia fructicola is the causal agent of brown rot of stone fruits in Brazil, causing major pre- and post-harvest losses. For many years, the demethylation inhibitor fungicide tebuconazole has been used as the most effective active ingredient for controlling brown rot, and as a result, strains of M. fructicola resistant to this ingredient have emerged in many Brazilian States producing stone fruits. The aim of this study was to investigate the mechanism(s) associated with the resistance of M...
July 11, 2017: Phytopathology
Jarred Hideki Yasuhara-Bell, Glorimar Marrero, Mohammad Arif, Asoka de Silva, Anne Alvarez
Dickeya and Pectobacterium spp. are responsible for soft rotting diseases of several plant species, some with overlapping host range. On potato, symptoms caused by these pathogens cannot be clearly differentiated. Disease results in the down-grading and rejection of potato seed, thus requiring additional phytosanitary restrictions across Northern Europe and other parts of the world. In an effort to provide a more timely and accurate diagnostic to distinguish these two groups of pathogens, a method for detecting Dickeya spp...
July 11, 2017: Phytopathology
Dalphy Harteveld, Michael Grant, Jay W Pscheidt, Tobin Peever
Mummy berry, caused by Monilinia vaccinii-corymbosi, causes economic losses of highbush blueberry in the US Pacific Northwest (PNW). Apothecia develop from mummified berries overwintering on soil surfaces and produce ascospores that infect tissue emerging from floral and vegetative buds. Disease control currently relies on fungicides applied on a calendar-basis rather than inoculum availability. To establish a prediction model for ascospore release, apothecial development was tracked in three fields, one in western OR and two in northwestern WA in 2015 and 2016...
July 11, 2017: Phytopathology
Jae Hoon Lee, Youfu Zhao
Erwinia amylovora, the causal agent of fire blight disease of apples and pears, employs intracellular proteases, including Lon and ClpXP, for post-translational regulation of various cellular proteins. It has been shown that Lon plays a critical role in E. amylovora virulence by directly targeting type III secretion (T3SS) proteins and the Rcs phosphorelay system. In this study, we genetically examined the role of ClpXP and its potential interaction with Lon in E. amylovora. Mutation in clpXP diminished the expression of the T3SS, reduced exopolysaccharide amylovoran production and motility, and resulted in delayed disease progress...
July 10, 2017: Phytopathology
Bhanu Priya Donda, Sridhar Jarugula, Rayapati A Naidu
Despite being the first closterovirus documented in grapevines (Vitis sp.), the molecular biology of Grapevine leafroll-associated virus 1 (GLRaV-1, genus Ampelovirus, family Closteroviridae) is still in its infancy. In this study, the complete genome sequence of two GLRaV-1 isolates was determined to be 18,731 (isolate WA-CH) and 18,946 (isolate WA-PN) nucleotides (nt). The genome of WA-CH and WA-PN isolates encodes nine putative open reading frames (ORFs) and the arrangement of these ORFs in both isolates was similar to that of Australian and Canadian isolates...
July 7, 2017: Phytopathology
Deanna Lillian Funnell-Harris, Erin D Scully, Scott E Sattler, Roy C French, Patrick M O'Neill, Jeffrey F Pedersen
Several Fusarium species cause sorghum [Sorghum bicolor (L.) Moench] grain mold, resulting in deterioration and mycotoxin production in the field and during storage. Fungal isolates from air (2005-2006), and from leaves and grain from wild-type and brown midrib (bmr)-6 and bmr12 plants (2002-2003), were collected from two locations. Compared with wild-type, bmr plants have reduced lignin content, altered cell wall composition and different levels of phenolic intermediates. Multilocus maximum likelihood analysis identified two Fusarium thapsinum operational taxonomic units (OTUs)...
July 7, 2017: Phytopathology
Bhabesh Dutta, David B Langston, Xuelin Luo, Jeremy Kichler, Scott Carlson, Ron Gitaitis
The phytopathogenic bacterium Xanthomonas euvesicatoria causes bacterial leaf spot (BLS) of pepper and has a worldwide distribution. BLS is difficult to control and an integrated management strategy that incorporates crop rotation, use of clean seeds and clean plants, weed control, resistant varieties, and applications of bactericides, biocontrol agents, and systemic acquired resistance (SAR) inducers is generally recommended. However, even with that arsenal of weapons, BLS can still be responsible for severe losses under favorable environmental conditions...
July 7, 2017: Phytopathology
Samuel Soubeyrand, Vincent Garetta, Caroline Monteil, Frederic Suffert, Henriette Goyeau, Julie Berder, Jacques Moinard, Elisabeth Fournier, Didier Bs Tharreau, Cindy Morris, Ivan Sache
The structure of pathogen populations is an important driver of epidemics affecting crops and natural plant communities. Comparing the composition of two pathogen populations consisting of assemblages of genotypes or phenotypes is a crucial, recurrent question encountered in many studies in plant disease epidemiology. Determining if there is a significant difference between two sets of proportions is also a generic question for numerous biological fields. When samples are small and data are sparse, it is not straightforward to provide an accurate answer to this simple question because routine statistical tests may not be exactly calibrated...
July 5, 2017: Phytopathology
Jillian Lang, Elysa DuCharme, Jorge Ibarra Caballero, Emily Luna, Terra Hartman, Mary Ortiz-Castro, Kevin Korus, John Rascoe, Tamra A Jackson, Kirk Broders, Jan Leach
Bacterial leaf streak of corn (Zea mays) recently reached epidemic levels in three corn-growing states, and has been detected in another six states in the central United States. Xanthomonas vasicola was identified as the causal agent of this disease. A multi-locus sequence alignment (MLSA) of six housekeeping genes and comparison of average nucleotide identity (ANI) from draft genome sequence were used to confirm phylogenetic relationships and classification of this bacterium relative to other Xanthomonas vasicola strains...
July 5, 2017: Phytopathology
Matheus Thomas Kuska, Anna Brugger, Stefan Thomas, Mirwaes Wahabzada, Kristian Kersting, Erich Christian Oerke, Ulrike Steiner, Anne-Katrin Mahlein
Differences in early plant-pathogen interactions are mainly characterized by using destructive methods. Optical sensors are advanced techniques for phenotyping host-pathogen interactions on different scales and for detecting subtle plant resistance responses against pathogens. A microscope with a hyperspectral camera was used to study interactions between Blumeria graminis f. sp. hordei and barley (Hordeum vulgare) genotypes with high susceptibility or resistance due to hypersensitive response (HR) and papilla formation...
June 30, 2017: Phytopathology
Krishna D Puri, Suraj Gurung, Dylan Pg Short, Zahi Atallah, German Sandoya, Mike Davis, Ryan J Hayes, Krishna V Subbarao
Understanding pathogen evolution over time is vital for plant breeding and deployment of host resistance. In the context of a soilborne pathogen, the potential of host-directed evolution of a Verticillium dahliae race 1 isolate and genotypic variation of V. dahliae associated with two major hosts (lettuce and tomato) were determined. A total of 427 isolates were recovered over six years from a resistance screening nursery infested with a single V. dahliae race 1 isolate. In a separate study, an additional 207 isolates representing 163 and 43 isolates from commercial lettuce and tomato fields were collected, respectively...
June 27, 2017: Phytopathology
Chad DeChant, Tyr Wiesner-Hanks, Siyuan Chen, Ethan L Stewart, Jason Yosinski, Michael A Gore, Rebecca Nelson, Hod Lipson
Northern leaf blight (NLB) can cause severe yield loss in maize, but scouting large areas to accurately diagnose the disease is time-consuming and difficult. We demonstrate a system capable of automatically identifying northern leaf blight (NLB) lesions in field-acquired images of maize plants with high reliability. This approach uses a computational pipeline of convolutional neural networks (CNNs) that addresses the challenges of limited data and the myriad irregularities that appear in images of field-grown plants...
June 27, 2017: Phytopathology
Kelsie Green, Mohamad Chikh-Ali, Randall Hamasaki, Michael J Melzer, Alexander Karasev
Poha, or Cape gooseberry (Physalis peruviana L.) is a plant species cultivated in Hawaii for fresh fruit production. In 2015, an outbreak of virus symptoms occurred on poha farms in the South Kohala District of the island of Hawaii. The plants displayed mosaic, stunting, leaf deformation, and produced poor fruit. Initial testing found the problem associated with Potato virus Y (PVY) infection. Six individual PVY isolates, named Poha1 to Poha6, were collected from field-grown poha plants and subjected to biological and molecular characterization...
June 27, 2017: Phytopathology
Jasper Depotter, Luis Rodriguez-Moreno, Bart Phj Thomma, Tom Wood
V. longisporum is an economically important fungal pathogen of brassicaceous crops that originated from at least three hybridization events between different Verticillium spp., leading to the hybrid lineages A1/D1, A1/D2 and A1/D3. Isolates of lineage A1/D1 generally cause stem striping on oilseed rape (Brassica napus), which has recently been reported for the first time to occur in the UK. Intriguingly, the emerging UK population is distinct from the north-central Europe stem striping population. Little is known about the pathogenicity of the newly emerged UK population, hence pathogenicity tests were executed to compare British isolates to previously characterized reference strains...
June 27, 2017: Phytopathology
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