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Begomoviruses and criniviruses, vectored by whiteflies (Bemisia tabaci), are important threats to crops worldwide. In recent years, the spread of cucurbit leaf crumple virus (CuLCrV), cucurbit yellow stunting disorder virus (CYSDV) and cucurbit chlorotic yellows virus (CCYV) on cucurbit crops has been reported to cause devastating crop losses in many regions of the world. In this study, a multiplex recombinase polymerase amplification (RPA) assay, an isothermal technique for rapid and simultaneous detection of DNA and RNA viruses CuLCrV, CYSDV and CCYV was developed. Highly specific and sensitive multiplex RPA primers for the coat protein region of these viruses were created and evaluated. The sensitivity of the multiplex RPA assay was examined using serially diluted plasmid containing the target regions. The results demonstrated that multiplex RPA primers have high sensitivity with a detection limit of a single copy of the viruses. The multiplex RPA primers were specific to the target as indicated by testing against other begomoviruses, potyviruses and an ilarvirus, and no nonspecific amplifications were noted. The primers simultaneously detected mixed infection of CCYV, CYSDV and CuLCrV in watermelon and squash crude extracts. This study is the first report of a multiplex RPA assay for simultaneous detection of mixed infection of DNA and RNA plant viruses. [ABSTRACT FROM AUTHOR]

Rose (Rosa spp.) is a very important ornamental shrub cultivated worldwide and of value for the pharmaceutical industry. The plant is broadly susceptible to pathogens, including viruses. Rose rosette virus (RRV; virus species Emaravirus rosae) causes multiple symptoms typically rosettes, ultimately leading to death. The virus transmission is by grafting and a wind‐dispersed eriophyoid mite, Phyllocoptes fructiphilus, which survives in winter‐dormant plants. Due to extensive globalization RRV is a threat for the European rose, landscape, nursery and tourism industries. The most common and reliable method used for RRV detection is RT‐PCR. Positive control is indispensable for PCR reliability and can be difficult to obtain for emerging or highly contagious pathogens and are subject to BSL‐2 quarantine. A synthetic artificial positive control (APC) using custom DNA inserts of sense and anti‐sense primers was designed de novo and inserted in a circular plasmid vector to create a positive control for use with most RRV reported primers and eriophyoid mites. This study describes a functional demonstration and development of a rapid, consistent, adaptable and cost‐effective alternative to infected true‐tissue positive control for detection of RRV. The inserted RRV primers are for end point and quantitative RT‐PCR, reverse transcription loop‐mediated isothermal amplification (RT‐LAMP), recombinase‐polymerase amplification (RPA), broad detection of emaravirus and the eriophyoid mite vector Phyllocoptes fructiphilus. The APC‐RRV and RRV infected rose (leaf tissue) were tested side to side. Results demonstrated APC‐RRV is a safe, cloneable and reliable approach subjected to quality control with application in quarantine surveillance and routine diagnostics of RRV. [ABSTRACT FROM AUTHOR]

Disease symptoms: Symptoms include water‐soaked areas surrounded by chlorosis turning into necrotic spots on all aerial parts of plants. On tomato fruits, small, water‐soaked, or slightly raised pale‐green spots with greenish‐white halos are formed, ultimately becoming dark brown and slightly sunken with a scabby or wart‐like surface. Host range: Main and economically important hosts include different types of tomatoes and peppers. Alternative solanaceous and nonsolanaceous hosts include Datura spp., Hyoscyamus spp., Lycium spp., Nicotiana rustica, Physalis spp., Solanum spp., Amaranthus lividus, Emilia fosbergii, Euphorbia heterophylla, Nicandra physaloides, Physalis pubescens, Sida glomerata, and Solanum americanum. Taxonomic status of the pathogen: Domain, Bacteria; phylum, Proteobacteria; class, Gammaproteobacteria; order, Xanthomonadales; family, Xanthomonadaceae; genus, Xanthomonas; species, X. euvesicatoria, X. hortorum, X. vesicatoria. Synonyms (nonpreferred scientific names): Bacterium exitiosum, Bacterium vesicatorium, Phytomonas exitiosa, Phytomonas vesicatoria, Pseudomonas exitiosa, Pseudomonas gardneri, Pseudomonas vesicatoria, Xanthomonas axonopodis pv. vesicatoria, Xanthomonas campestris pv. vesicatoria, Xanthomonas cynarae pv. gardneri, Xanthomonas gardneri, Xanthomonas perforans. Microbiological properties: Colonies are gram‐negative, oxidase‐negative, and catalase‐positive and have oxidative metabolism. Pale‐yellow domed circular colonies of 1–2 mm in diameter grow on general culture media. Distribution: The bacteria are widespread in Africa, Brazil, Canada and the USA, Australia, eastern Europe, and south‐east Asia. Occurrence in western Europe is restricted. Phytosanitary categorization: A2 no. 157, EU Annex designation II/A2. EPPO codes: XANTEU, XANTGA, XANTPF, XANTVE. [ABSTRACT FROM AUTHOR]

Bacterial wilt of tomato caused by Ralstonia solanacearum species complex (RSSC) causes substantial yield losses in the tropics and subtropics. Disease management options by chemicals are limited, and host resistance is the cheapest and easiest means of control. However, sources of bacterial wilt resistance in tomato are limited. The disease often coincides with higher temperatures in the tropics, and resistance sources that are more heat stable are particularly valuable for breeding of tropically adapted tomato cultivars. The objectives of this study were to identify tomato accessions that demonstrate relatively high bacterial wilt resistance under high temperatures and to identify accessions that may possess QTLs other than Bwr‐6 and Bwr‐12 (two major disease resistance QTLs against bacterial wilt), which could be exploited in future breeding. Sixty‐seven tomato entries reported as bacterial wilt resistant were evaluated in a greenhouse against one strain each of phylotype I (Pss4) and phylotype IIB (Pss1632) of the RSSC (average temperature ≥29°C). Of those, five and 19 were homozygous for Bwr‐6 and Bwr‐12, respectively, and six were homozygous for both QTLs. Bwr‐12 contributed to resistance against phylotype I strain but not against the phylotype II strain. Bwr‐6 contributed to resistance against both phylotype strains. Entries with both QTLs as a group performed relatively better against the phylotype I strain. Entry "94T765‐24‐79", which lacked Bwr‐6 and Bwr‐12, demonstrated relatively high resistance against the phylotype II strain and may carry new QTL/s. As new bacterial wilt resistance QTLs are mapped and markers designed, pyramiding multiple bacterial wilt resistance QTLs into new varieties should be straightforward, thereby increasing the chances of obtaining stable resistance. [ABSTRACT FROM AUTHOR]

Taxonomic status Bacteria; Phylum Proteobacteria; Class Gammaproteobacteria; Order Xanthomonadales; Family Xanthomonadaceae; Genus Xanthomonas; Species Xanthomonas euvesicatoria, Xanthomonas vesicatoria, Xanthomonas perforans and Xanthomonas gardneri. Microbiological properties Gram-negative, rod-shaped bacterium, aerobic, motile, single polar flagellum. Host range Causes bacterial spot disease on plants belonging to the Solanaceae family, primarily tomato ( Solanum lycopersicum), pepper ( Capsicum annuum) and chilli peppers ( Capsicum frutescens). Disease symptoms Necrotic lesions on all above-ground plant parts. Distribution Worldwide distribution of X. euvesicatoria and X. vesicatoria on tomato and pepper; X. perforans and X. gardneri increasingly being isolated from the USA, Canada, South America, Africa and Europe. A wide diversity within the bacterial spot disease complex, with an ability to cause disease at different temperatures, makes this pathogen group a worldwide threat to tomato and pepper production. Recent advances in genome analyses have revealed the evolution of the pathogen with a plethora of novel virulence factors. Current management strategies rely on the use of various chemical control strategies and sanitary measures to minimize pathogen spread through contaminated seed. Chemical control strategies have been a challenge because of resistance by the pathogen. Breeding programmes have been successful in developing commercial lines with hypersensitive and quantitative resistance. However, durability of resistance has been elusive. Recently, a transgenic approach has resulted in the development of tomato genotypes with significant levels of resistance and improved yield that hold promise. In this article, we discuss the current taxonomic status, distribution of the four species, knowledge of virulence factors, detection methods and strategies for disease control with possible directions for future research. [ABSTRACT FROM AUTHOR]

Gummy stem blight (GSB) is one of the most destructive foliar diseases of cucurbits, worldwide. To identify and characterize the pathogen which causes GSB on watermelon and muskmelon in East China, morphological characteristics, pathogenicity assays as well as sequence characterization of the rDNA internal transcribed spacer (ITS) were performed on 41 isolates collected from Jiangsu, Zhejiang, Anhui and Jiangxi provinces. The mycelia of all the isolates were white on top and olivaceous green to black with concentric circles at the bottom on potato-dextrose agar medium. The isolates differed significantly on aggressiveness based on pathogenicity assays. rDNA-ITS sequences and phylogenetic analysis confirmed the isolates as Didymella bryoniae. The isolates were found to be highly identical with the exception of 13 isolates, which had a guanine substitution instead of adenine at position 131 of the ITS. [ABSTRACT FROM AUTHOR]