Category Archives: SHORT COMMUNICATION

Rapid and visual detection of grapevine fleck virus using recombinase polymerase amplification combined with lateral flow strips

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Abstract

Grapevine flack virus (GFkV) causes fleck disease and leads to severe symptoms when the infection occurs with multiple viruses. Restricting the propagation of GFkV-infected grapevines is the ideal management strategy to control the spread of this virus. Therefore, the development of rapid detection methods for GFkV is urgently required. In the present study, we developed a rapid and reliable assay based on the reverse transcription-recombinase polymerase amplification (RT-RPA) combined with lateral flow strips (LFS) using sequence-specific primers and a probe-based coat protein sequences for the GFkV detection in grapevines. The GFkV RT-RPA-LFS assay was optimized at 38°C for 10 min and an extra 5 min LFS incubation time. The optimized RT-RPA-LFS assay had similar sensitivity to RT-PCR and showed no cross-reaction with major viruses infecting grapevines in Korea. The assay was successfully validated for GFkV detection in grapevine field samples. This study provides a reliable technique for rapidly detecting GFkV as an alternative diagnostic approach for producing virus-free grapevine nurseries.

Detection of a PCR‐based mating type for native intraspecific Beauveria bassiana isolates

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Abstract

This study developed a PCR-based mating-type analysis of 30 intraspecific Beauveria bassiana isolates after ITS phylogenetic analysis. Out of 30 isolates, only 11 B. bassiana isolates, viz., Bb4, Bb5, Bb11, Bb18, Bb19, Bb20, Bb23, Bb25, Bb27, Bb28, and Bb29, exhibited amplification of the mating-type loci and were thought to be heterothallic. All of these isolates, with the exception of Bb20, had MAT1 mating-type amplification. All these 11 isolates were clustered together with the MAT1- and MAT2-specific reference strains of B. bassiana in the maximum likelihood phylogenetic analysis of mating-type genes (IFO 31953 and IFO 31676, respectively). Although the PCR products obtained by the mating-type assay were short, the phylogenetic trees of the mating-type genes gave better resolution than that of the ITS region. Understanding the mating type of fungi can clarify the biological species concept and the identification of sex-related genes in fungi without the presence of teleomorphs. So, combining phylogenetic, developmental, and mating research on each teleomorph specimen has the potential to clarify the systematics of Beauveria species.

Identification of Clonostachys rogersoniana as a causal agent of sisal leaf blight disease in South China

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Abstract

A novel strain of leaf blight disease affecting sisal leaves was discovered at the Hongshan farm of Yulin City, Guangxi Province, in 2022. Ten fungal isolates were identified in the infected sisal leaves and classified into six categories (22GX3-1 to 6). Pathogenicity testing revealed that only 22GX3-2 and two morphologically similar isolates induced symptoms similar to those detected in the field. Based on morphological analysis and nucleotide sequencing of the internal transcribed spacer (ITS) of the rRNA gene, translation elongation factor 1 alpha (TEF1) and tubulin beta chain 2 (TUB2) genes, the fungal isolate 22GX3-2 was identified as Clonostachys rogersoniana. To the best of our knowledge, this is the first study reporting sisal leaf blight caused by Clonostachys rogersoniana.

Powdery mildew of chayote (Sechium edule) caused by Podosphaera xanthii race 2 in Brazil

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Abstract

The causal agent of chayote (Sechium edule) powdery mildew (PM) was identified in Brazil. Microscopic examinations revealed hyaline and ovoid conidia, borne in chains and displaying distinctive extra-vacuolar fibrosin bodies. Morphology agreed to the standard description of the anamorph of Podosphaera xanthii. To confirm this identification, genomic DNA was extracted from field isolates and used in PCR assays with ITS primers. Amplicons were Sanger-sequenced and the nucleotide alignments of all isolates displayed identity levels above 97% with P. xanthii isolates in GenBank database. Phylogenetic analyses indicated only P. xanthii isolates as the PM-inducing pathogens in chayote. Inoculation assays were performed using chayote, zucchini and a set of muskmelon differential cultigens for determination of the physiological races of P. xanthii. All chayote isolates were pathogenic to chayote and zucchini seedlings. Five isolates were also pathogenic to the muskmelon cultigens ‘Hale's Best Jumbo’, ‘Védrantais’, ‘PMR-45’ and ‘Edisto 47’, whereas ‘PMR-5’ was asymptomatic during the experimental period. The virulence profile of chayote-infecting isolates allowed their classification as P. xanthii race 2. To the best of our knowledge, this is the first worldwide report of P. xanthii race 2 in chayote. This report has relevant epidemiological and disease management implications, allowing more sustainable chayote cultivation under tropical and subtropical conditions.

Occurrence of copper‐resistant Pseudomonas syringae pv. actinidiae strains in kiwifruit orchards of Central Italy

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Abstract

Bacterial isolates belonging to Pseudomonas syringae pv. actinidiae, the causal agent of kiwifruit bacterial canker, have been isolated, during 2021 and 2022, from Actinidia chinensis orchards of Central Italy planted with cultivars Hayward and Zespri G3®. A total of 23 isolates were obtained from twigs and leaves that showed the typical symptoms of bacterial canker, including leaf spotting and twig canker. All of them showed resistance to 1.2 mM copper sulphate added to mannitol–glutamate–yeast extract (MGY) medium. No other Pseudomonas syringae pv. actinidiae strains were isolated from the orchards. The P. s. pv. actinidiae strains that showed resistance to copper have the copA and copD genes that regulate the efflux of copper through the inner membrane and the copper sensor copS gene. They do not possess the cusABC complex that confers resistance to high concentration of copper. Representative copper-resistant strains were proven pathogenic to kiwifruit plants upon artificial inoculation. This is the first record of copper-resistant P. s. pv. actinidiae strains in Italy and, as far as we know, in Europe.

Characterization of sugarcane mosaic virus from Cymbopogon spp. plants in Brazil

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Abstract

In April 2022, virus-like symptoms were observed in a Cymbopogon spp. plant grown in the backyard of a house and in Java citronella (C. winterianus) plants in a flower shop in Piracicaba, São Paulo State, Brazil. In April 2023, ca. 700,000 Ceylon citronella (C. nardus) plants showing symptoms of mosaic were observed in a field crop in Dois Corrégos (SP). Evidence for a possible potyvirus infection was revealed by electron microscopy and confirmed by molecular assays. Nucleotide sequencing of amplicons from RT-PCR identified the potyvirus infecting a Cymbopogon spp. plant, Java and Ceylon citronella as sugarcane mosaic virus (SCMV, genus Potyvirus). Phylogenetic analysis of the coat protein gene indicated that the SCMV isolates from Cymbopogon (C1), Java (JC1), and Ceylon citronella (CC) belong to the clade of SCMV from sugarcane. The C1 isolate, and an isolate from sugarcane (SCMV-SU) (control) were mechanically transmitted to Java citronella, sorghum, sugarcane and maize plants. Aphis gossypii transmitted the C1 and SU isolates to Java citronella plants, while Melanaphis sacchari transmitted only the SU isolate to Java citronella plants. This is the first molecular characterization of SCMV from Cymbopogon spp. plants.

Meloidogyne arenaria infecting Matricaria chamomilla in Brazil

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Abstract

Plants of Matricaria chamomilla L. (Asteraceae), well-known medicinal species, showing root galls, were collected in Pelotas, state of Rio Grande do Sul (Brazil). Based on morphological (perineal patterns and males), morphometric (males) and esterase phenotypes (Est A2), we identified the infecting nematode as the root-knot nematode M. arenaria. Under greenhouse conditions, four M. chamomilla plants were inoculated with about 1000 specimens obtained from the isolate. We observed about 207 ± 72 nematodes g−1 of roots, confirming its pathogenicity. To the best of our knowledge, this is the first record of M. arenaria parasitizing M. chamomilla in Brazil and elsewhere.

Pythium and related species on blueberry plants in South Africa

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Abstract

The blueberry industry is one of the successful and expanding agricultural cropping systems in South Africa. As a result of this growth, research into identifying plant disease agents has become increasingly important, yet there are relatively few scientific reports published on the subject in the country. The aim of this study was to identify the causal agents of stunting and leaf scorch on blueberry plants and evaluate their pathogenicity. Root samples were collected from a commercial southern highbush blueberry planting in North West, South Africa. The resulting isolates were identified based on sequence data from the rDNA-ITS. Three Pythiaceae were identified including Globisporangium ultimum var. sporangiiferum, Globisporangium splendens and Pythium aphanidermatum. Results of pathogenicity trials showed that the isolated species were able to cause disease on 40% of the plants. This is the first official report for G. ultimum var. sporangiiferum in South Africa and the first report of G. ultimum var. sporangiiferum and P. aphanidermatum from blueberry plants.