Tropical Plant Pathology最新文献

Foot rot disease caused by Phytophthora capsici is one of the most destructive diseases of black pepper in Vietnam and worldwide. However, other oomycete species such as P. tropicalis and Pythium deliense reported as serious threats to black pepper in India have also been recorded on this plant. The population of oomycetes occurring in black pepper plantations in Vietnam and their pathogenicity have not been investigated in the last decade. To this end, two hundred fifteen oomycete isolates were collected from the root rots and rhizospheric soil of black pepper in the Central Highlands and the Southeast region of Vietnam. Of these, 23 isolates were representatively chosen based on their origin and morphology for DNA sequence analysis of the internal transcribed spacer region, then 11 isolates were further selected for the translation elongation factor 1-alpha and the beta-tubulin gene analyses. Morphology and molecular analyses indicated that P. capsici, P. cinnamomi, P. heveae, P. nicotianae, P. parvispora, P. tropicalis, Phytopythium vexans, and a new species candidate Phytopythium sp. were identified among oomycete isolates. Of these, P. capsici and P. tropicalis could be the prevalent species in black pepper plantations in studied areas. The inoculation tests demonstrated that P. capsici, P. nicotianae and P. tropicalis were pathogenic on both leaves and roots of black pepper. Phytopythium vexans was pathogenic on root only. Meanwhile, P. cinnamomi, P. heveae, P. parvispora and Phytopythium sp. were non-pathogenic.

Chilli, an important vegetable cum spice crop in India, is affected by various biotic and abiotic factors, which leads to a significant reduction in the growth and yield of the chilli crop. One of the most prominent biotic factors posing threat to chilli production in southern parts of India especially, in Tamil Nadu is begomoviruses (Family Geminiviridae). Begomoviruses are transmitted by the insect vector, whitefly (Bemisia tabaci) and they cause curling, yellowing, puckering, and reduction in the size of the leaf in the infected chilli plants. In this study, molecular (PCR) diagnostics were used to detect the presence of begomovirus, betasatellite, and six begomovirus species viz tomato leaf curl New Delhi virus (ToLCNDV), tomato leaf curl Bangalore virus (ToLCBV), tomato leaf curl Palampur virus (ToLCPalV), tomato leaf curl Gujarat virus (ToLCGV), tomato leaf curl Joydebpur virus (ToLCJoV) and chilli leaf curl virus (ChiLCV), in the chilli samples collected from the major chilli growing areas of all the five agro-climatic zones of Tamil Nadu state of India. A total number of 833 samples collected from different locations in Tamil Nadu during the period of 2018-2022 were analysed by generic as well as species-specific PCR. The PCR results of 833 samples showed positive amplification of 20.5% for generic, 13.4% for beta satellite, 42.1% for ChiLCV, 17.8% (ToLCNDV), 16.6% (ToLCGV), 6.7% (ToLCBV), 2.2% (ToLCPalV), and 0.7% for ToLCJoV specific primers respectively. The percentage of mixed infection of two or more than two begomoviruses among the total samples is 39.2. Our study has shown that the ChiLCV and multiple tomato-infecting begomoviruses were prevalent in the major chilli-growing areas of Tamil Nadu. The present study also showed that species of begomovirus infecting chilli plants in Northern and Southern India have a differential distribution.

For decades, the grapevine has been produced as a commercial fruit crop in Morocco. From 2004 to 2022, the area dedicated to cultivating and producing grapes has increased across the country. Despite the implementation of adequate agricultural practices, grapevine trunk diseases (GTDs) lead to significant yield losses and a remarkable reduction in viticultural quality. Many grape growers encounter this issue in their vines each year and seek strategies to cope with it. In the most significant grape-growing regions globally, including Morocco, grapevine decline is a common and significant disease that is brought on by a multitude of latent fungal plant diseases. Due to the use of poorly informative markers in phylogenetic analyses and the lack of relevant morphological characteristics, the classification of these pathogens has proven to be challenging. Numerous genera and families have not yet been extensively studied, especially in Morocco. To identify the dieback-causing agents, surveys were carried out in 152 Moroccan vineyards in Marrakech-Safi, Casablanca-Settat, Rabat-Sale-Kenitra, and Fez- Meknes regions between 2019-2021. Samples of symptomatic trunks were collected and processed for mycological analysis. Afterward, fungal identification of representative isolates was performed combining morphological characterization and phylogenetic analysis based on the internal transcribed spacer (ITS) region of ribosomal DNA and protein-coding gene (β-TUB). Pathogenicity tests were fulfilled under greenhouse conditions for 15 days. Among the fungi collected in the current study, 54 fungal isolates were obtained belonging to different genera and families namely: Botryosphaeria (11 species), Fusarium (10 species), Pestialiotiopsis (4 species), Clonostachys (3 species), Entoleuca mammata, Phaeoacremonium hungaricum, Trichothecium roseum, Diaporthe ampelina, Epicoccum nigrum, Alternaria alternata, and Rosellinia convexa. Pathogenicity test revealed that Diplodia mutila, Neoscytalidium novaehollandiae, Neopestalotiopsis vitis, and Trichothecium roseum isolates are the most pathogenic. This is the first detailed report of species associated with GTDs in Morocco where new records of species worldwide are highlighted.

Papaya sticky disease (PSD) is an emerging disease-causing significant crop loss in some of the major papaya-growing regions of the world. The vectors of the PSD associated viruses in Brazil are still unknown. The papaya meleira virus complex comprised of a fusagra-like virus, papaya meleira virus (PMeV), and a umbravirus-like associated RNA (ulaRNA), papaya meleira virus 2 (PMeV2) is found infecting diseased papaya plants in Brazil. PMeV capsid protein packages both PMeV and PMeV2 genomes separately resulting in virions with the same morphology. Epidemiological analyses attributed fruit thinning as a mechanical mechanism responsible for the spread of sticky disease, but an aerial vector was not ruled out. Hemipteran insects have been implicated as vectors but a definitive conclusion on the biologically relevant vector has not been reached. Cicadellids have a population peak a month before the peak of papaya sticky disease incidence in the field and their ability to acquire and transmit the Mexican isolate of PMeV has been demonstrated. Whitefly (Bemisia tabaci MEAM1) is not considered a papaya pest in Brazil but has been reported to occur in plants near papaya trees and they transmit an Ecuadorian virus similar to PMeV2. In Brazil, Trialeurodes variabilis which colonizes papaya trees can acquire, but not transmit the PMeV complex. In this review, we discuss transmission assays and epidemiological analysis conducted in the last 30 years; the similarity of the PMeV complex capsid protein with viruses that infect fungi; the challenges imposed by laticifers, a well-known plant defense structure, in the acquisition of viral particles; and the presence of PMeV2. Elucidation of the PMeV complex vector would contribute to the efficient management of papaya sticky disease and increase understanding of the transmission mechanisms of plant-infecting fusagra-like viruses.

A survey of common bacterial blight (CBB) was conducted in common bean fields in Brazil, in the state of Goiás and in the Federal District. Isolation from symptomatic leaves on a semi-selective medium yielded yellow, mucoid colonies typical of Xanthomonas, and 161 pure cultures were obtained. PCR with specific primers for X. phaseoli pv. phaseoli and X. citri pv. fuscans was performed and confirmed the presence of both fuscans and GL2 strains of X. citri pv. fuscans and the presence of X. phaseoli pv. phaseoli. However, for 81 isolates, PCR results were negative. Housekeeping genes gyrB and rpoD sequences placed these strains in the provisionally named X. cannabis species clade, clustering pv. zinniae, pv. esculenti, and the strain Nyagatare, isolated from beans in Rwanda in 2013. The identification of a subset of 20 strains was complemented by a positive PCR with Xanthomonas-specific primers that amplify a portion of the gumD gene and the induction of hypersensitive reaction in tomato leaves within 24-48 hours. Pathogenicity was confirmed by inoculation on the French common bean cv. Flavert and the Brazilian common bean cv. BRS Ártico. Symptoms such as white spots along the leaf blade, leaf curling, and wilting developed in inoculated plants. Partial gyrB and rpoD sequences analyses revealed identity values ranging from 98.3 to 100% between the Brazilian isolates and strain Nyagatare, proposed as X. cannabis pv. phaseoli.

Phytoplasmas are uncultivable wall-less bacteria causing plant diseases worldwide. Phytoplasmas from X-disease are one of the most diverse and economically important in South America. The Cicuta witches' broom Phytoplasma (CicWB) was described in association to cicuta or hemlock (Conium maculatum L.) exhibiting witches' broom and phyllody symptoms in surrounding potato fields in Los Cerrillos (Córdoba- Argentina). The partial genome of CicWB phytoplasma was obtained using a hybrid approach combining Illumina and Oxford Nanopore Technologies. Final draft genome consists of 16 contigs totaling 758.187 bp of length, with 400X of coverage and 96.70% of the estimated completeness. Comparative genomics, based on Average Nucleotide Identity (ANI), digital DNA-DNA hybridization (dDDH), and phylogenomic analyses, revealed its close relationship to subgroup 16SrIII-J phytoplasmas. Furthermore, the study identified 37 putative effectors, including orthologs for SAP11, SAP54, SAP05, as well as immunodominant membrane proteins Imp and IdpA. This comprehensive genome analysis provides crucial insights into the genomic landscape of phytoplasmas in the region, contributing to our understanding of their diversity and pathogenicity.

Wheat (Triticum spp.) is a global staple food crop, contributing significantly to the world's food security. Understanding and harnessing the genetic diversity within wheat cultivars is paramount for developing resilient and high-yielding varieties. The present study reports rust response of 31 registered rust resistant genetic stocks of wheat against recently identified and most virulent pathotypes of all three rust pathogens and their morphological and molecular diversity assessment. Analysis of variance (ANOVA) showed indicated significant differences among the genotypes for all the studied traits. Among 31 genetic stocks 30, 15, and 8 were found resistant against all the tested pathotypes of stem, leaf and stripe rust pathogens, respectively, whereas only two (FLW21 and FLW28) conferred resistance against all three rusts. Molecular profiling with 59 polymorphic SSRs resulted in 194 alleles with an average 3 alleles/loci. With an average of 0.54, the Polymorphism Information Content (PIC) varied from 0.34 to 0.75, reflecting higher allelic variation. The average gene diversity, heterozygosity, major allele frequency, and minor allele frequency were 0.61, 0.31, 0.48, and 0.52, respectively. Cluster analysis grouped 31 genetic stocks into 3 clusters. The AMOVA revealed that within population variation was higher than between them (76% vs. 24%). Clustering was further supported by the structure and Principal Coordinate Analysis (PCoA). Structure analysis grouped the genetic stocks into three sub-populations. These findings will help in suggesting different cross combinations for wheat rust resistance breeding and pyramiding of multiple rust resistance genes.

Floriculture is one of the most significant crop industries worldwide. The carnation is the second-most exported or imported flower in the world. The disease most affecting the carnation crop is fusariosis, produced by the ascomycete Fusarium oxysporum f.sp. dianthi. Little is known about the genetics of the resistance to Fusarium in carnations. we identified different genes implicated direct or indirect forms in the defense mechanisms were 16 identified using mRNAseq and RT-qPCR techniques. Some of these genes were involved in basal metabolism, genes implicated in the primary response to the pathogen, and Pathogenesis-related proteins (PR) genes. These genes in different carnation varieties present overexpression or, in contrast, subexpression and somehow determine the resistant or susceptible phenotype to Fusarium oxysporum. Some of them are directly related to cell wall remodeling. Different genes are involved in the resistant response in carnations in different varieties; so, each variety elaborates a response in a different form from the other varieties; even more, the same gene is expressed differently in the different resistant varieties.

Tobacco (Nicotiana tabacum L.), an endemic species of South America that is grown worldwide, is a member of the Solanaceae family. Although it is not a common crop in Ecuador, tobacco is important to the nation's economy and a significant source of employment. Viral infections are particularly devastating to tobacco as they can reduce both its yield and quality. In July 2021, symptoms of chlorosis, mosaic and leaf distortion were observed in four commercial fields in the provinces of Guayas and Los Ríos in Ecuador. This study aims to comprehensively characterize a viral isolate obtained from symptomatic plants. Using high throughput sequencing (HTS), phylogenetic analysis of the different open reading frames, and transmission electron microscopy (TEM) of symptomatic plants, we report for the first time the molecular characterization and genome sequence of Cucumber mosaic virus (CMV) isolated from commercial tobacco plants in Ecuador. The ability to detect and identify CMV in tobacco commercial plant fields enables the development of efficient control strategies, thereby mitigating constraints on the production of high-quality tobacco leaves.

Fungicide resistance is an alarming challenge for the Brazilian tropical agricultural systems, with major implications for food safety, human and animal health, as well as for the environment. This review explores strategies to address fungicide resistance within the Brazilian agroecosystem context. We examined historical and current scenarios of fungicide resistance in the Brazilian agroecosystems and the approaches to delay the emergence and mitigate the selection of resistant variants. Our review indicates that the prevalence of resistance in field populations of key plant pathogens in Brazil was due to failures in the implementation of preventive measures. To address this issue, alternative evolutionary-smart strategies against fungicide resistance are proposed, emphasizing institutional actions and public policies. Crucial steps involve strengthening national networks for large-scale foliar and seed fungicide efficacy testing and resistance monitoring, as well as imposing tighter restrictions on the labeling of high-risk single-active formulations. Additionally, the integration of non-chemical disease management strategies and the establishment of a centralized database and information system on fungicide resistance in Brazil are identified as essential for effective resistance monitoring and informed decision-making. To enhance fungicide resistance management, the adoption of a warning system (e.g., based on aerobiology- or on weather-monitoring) for predicting disease epidemics and minimizing fungicide applications is recommended. Increased funding, collaboration, mandatory reporting, and capacity building are required to overcome these challenges. In addition, promoting integrated disease management approaches is vital. By implementing these tailored strategies, Brazil can actively contribute to safeguarding its food safety, protecting human and animal health, and preserving the delicate balance of its unique agroecosystem. The adoption of evolutionary-smart strategies against fungicide resistance will prolong fungicide efficacy, reduce economic costs, and minimize environmental impacts, ensuring sustainable and resilient agriculture in Brazil.