European Journal of Plant Pathology最新文献

Viruses are the causal agent of some of the most limiting diseases in Rubus crops. In this regard, a detailed knowledge of the Rubus virome is essential for successfully implementing mitigation strategies and assessing the risk of the emergence of novel viral diseases. Fortunately, the widespread use of RNA sequencing to characterize diverse aspects of the biology of Rubus species can also be a valuable source of data on viruses associated with these hosts. Here, we present a meta-analysis of the Rubus virome based on the re-examination of public RNAseq data from nine Rubus species and 23 hybrid cultivars worldwide. As a result, we identified 23 viruses and one viroid associated with the genus Rubus. Detected viruses are part of eleven families and 26 genera. We also provide evidence of a second species in the genus Brambyvirus, and a novel member of the family Virgaviridae. Our data also revealed raspberry bushy dwarf virus (RBDV) to be the most prevalent and generalist Rubus virus. With respect to the number of species, the genus Ilarvirus and the family Closteroviridae were the most diverse taxonomic ranks affecting Rubus. Network analysis revealed distinct Rubus viromes in different countries and analysis of coinfections revealed three main viral communities infecting these plant species across the world. We also provide information on virus variants from new locations worldwide and data on potential emergent viruses from other plant hosts.

Abstract

As very limited information is available on viruses and viroids infecting plum in India, virome analysis was undertaken to determine the virus and viroid spectrum infecting plum. High throughput sequencing (HTS) analysis of five plum samples (PM1-PM5) revealed the presence of near complete genome sequences of prunus necrotic ringspot virus (PNRSV), American plum line pattern virus (APLPV), apple chlorotic leaf spot virus (ACLSV) and hop stunt viroid (HSVd) in PM1; little cherry virus 1 (LChV-1), plum bark necrosis stem pitting-associated virus (PBNSPaV), ACLSV and HSVd in PM2. No virus or viroid sequence was obtained in PM3, PM4 and PM5. Near complete genome sequences of these viruses were obtained using different assemblers. APLPV, LChV-1, PBNSPaV and HSVd are being reported here for the first time from plum in India. The presence of these viruses was also confirmed by reverse transcription polymerase chain reaction and Sanger sequencing in HTS samples as well as in additional 36 plum samples (PM6-PM41) collected from the same orchard from where PM1 and PM2 samples were obtained. The validation test in an additional 36 samples indicated predominance of APLPV and PNRSV which were detected in all the samples, while other viruses were present only in some of the samples. Moreover, fragments per kilobase of transcript per million reads mapped and virus accumulation studies showed dominance of PNRSV RNA3 in PM1 and LChV-1 in PM2. Analysis of single nucleotide variants (SNVs) showed that PNRSV RNA3 had the highest SNVs (99) and PBNSPaV had the lowest SNVs (1). The phylogenetic analysis revealed that these viruses are phylogenetically related to viruses from different countries. These findings advance our knowledge of the viral pathogens of plum, and would help in virus indexing and certification of clean plant for commercial plum cultivars.

Graphical abstract

Grapevine crown gall (GCG), caused by tumor-inducing strains of Allorhizobium vitis (= Rhizobium vitis), is a threat to grapevines around the world. Previously, nonpathogenic A. vitis strain ARK-1 emerged as a promising biological control agent, demonstrating remarkable efficacy in root soaking procedures before planting. This study aims to evaluate the treatment effects when applying soil injection procedures post-planting, both in greenhouse and field experiments. The results of the treatment effects obtained from 21 experiments over 9 years (2009 to 2017) were analyzed and evaluated by a general linear mixed model (GLMM) and a network meta-analysis (NMA). The GLMM results revealed a significant association between the factors "soil injection" and "root soaking" with biological control activity. Subsequently, the NMA results showed that the estimated relative ratio (RR) following root soaking and soil injection treatments with ARK-1 was 0.16 and 0.30, respectively. In summary, while the control efficacy of root soaking with ARK-1 exceeded that of soil injection, the latter method also proved effective in managing GCG. Therefore, soil injection is recommended as a viable approach for GCG control.

Phytopathogens are a major concern for crop production, affecting the global food demand. To address this issue, chemicals are widely employed that adversely affect the ecosystem. A sustainable alternative is essential to control phytopathogens for sustained crop productivity. Essential oils are potential alternative sources for efficient and sustainable management of phytopathogens. In this study the activity of six popular essential oils from medicinal plants, namely Cymbopogon flexuosus, Cymbopogon winterianus, Curcuma aromatica, Pogostemoncablin, Mentha arvensis and Cymbopogon martini, against the devastating pathogenic microbes Ralstonia solanaceaerum, Xanthomonas campestris, Magnaporthe oryzae and Bipolaris oryzae was tested.

Essential oils derived from C. winterianus and C. flexuosus were shown to be most effective at 5% concentration against the tested bacteria and fungus in vitro. Scanning electron microscopy analysis also revealed the effectiveness of C. winterianus and C. flexuosus essential oils against both microbial phytopathogens R. solanacearum and X. campestris. Further, the compounds found in these essential oils were identified by Gas Chromatography-Mass Spectroscopy and systematic in silico molecular docking analysis. The potential compounds responsible for the growth inhibition of microbial phytopathogens were bio-active compounds ( +)-aromadendrene, linalyl anthranilate and caryophyllene from C. flexuosus. Moreover, C. flexuosus showed high binding affinity towards bacterial, fungal, and insect target proteins. In a nutshell, the study revealed the potential of C. flexuous and C. winterianus as broad-spectrum biocontrol agents against major microbial plant pathogens.

Citrus Huanglongbing (HLB) disease, also known as “citrus greening”, is currently considered the most devastating citrus disease due to its rapid spread, and high severity. Presently, research efforts are focused on searching for either curative treatments or resistant cultivars to combat the HLB-associated bacterium ‘Candidatus Liberibacter asiaticus’ (CLas).

Metabolomics can help to unravel the mechanisms supporting the potential tolerance/resistance of citrus relatives. Herein, we carried out a metabolomic analysis to determine whether the level of resistance of nine citrus-related genotypes is influenced by their pre-existing metabolic background before infection. For this purpose, the healthy phloem of nine Citrinae genotypes previously categorized according to their different responses to HLB was analyzed. A total of 53 different metabolites were targeted, including amino acids, organic and inorganic acids, and sugars. Interestingly, we observed that resistant and partially resistant genotypes exhibited higher accumulations of organic acids such as quinic acid and citric acid. In contrast, the amount of total sugars showed a clear upward trend in the susceptible genotypes. Notably, within this last group of metabolites, sugar acids increase in both partially resistant and resistant accessions, being more evident in the resistant group.

Alterations potentially linked to resistance levels were detected in specific amino acids belonging to the aspartate and glutamate families. Notably, only lysine levels exhibited a significant increase in the susceptible cultivars. The evaluation of five genes associated with lysine catabolism by RT-qPCR revealed differences in transcript abundance between resistant and susceptible samples suggesting a potential key role in plant defence. These findings open a new avenue to identify metabolites and/or substances that could aid in developing resistance strategies to this devastating disease.

The current work describes a biological method to create silver nanoparticles (AgNPs) using jojoba oil. As a reducing and capping agent, jojoba oil was utilized in the production of AgNPs. AgNPs may be classified by their UV-VIS, FTIR, and spectra. A transmission electron microscope (TEM) was used to examine the shape and size of the silver nanoparticles. The average size of the synthesized silver nanoparticles was 25.6 ± 10.3 nm, and they had a spherical shape. According to FTIR spectroscopy tests, the silver nanoparticles' surface had organic molecules bound to it. Five bacterial isolates were isolated and tested for pathogenicity on potatoes. All isolates produced the typical symptoms of soft rot disease. Isolate Pcc2 caused the highest disease severity (45%). According to 16sRNA, isolate Pcc2 was identified as Pectobacterium carotovorum subsp. carotovorum. Increasing the dosage of AgNPs increased the antibacterial effect against P. carotovorum. From these results, we can conclude that the use of AgNPs is a safe method for controlling postharvest potato diseases caused by Pectobacterium carotovorum subsp. carotovorum.

Paramyrothecium comprises saprobic and plant pathogenic members. Eight plant-pathogenic Paramyrothecium species have been recorded in Asia, America, and some parts of Africa and Europe. Among the commonly reported species are P. roridum and P. foliicola. Several Paramyrothecium species are associated with coffee leaf spots, muskmelon crown rot, and eggplant crater rot. Paramyrothecium is commonly found in soil, decaying plant material, and diseased fruits, stems, and leaves of several plant species. The life cycle of Paramyrothecium species includes an asexual stage throughout disease development, with no sexual morphs reported. Environmental factors, such as temperature and humidity, influence the distribution and prevalence of Paramyrothecium. Paramyrothecium-associated diseases occur through various mechanisms, including wind and rain dispersal of conidia, contaminated soil, and plant debris. Paramyrothecium disease development can be exacerbated when the soil is wet and plant tissues are damaged, which served as pathogen entry. Adequate water management, soil sanitation, and proper handling of crops are important to minimize losses in commercial crop production. Several biological control agents and pesticides have also been reported to control the pathogen and the associated disease.

Flavescence dorée (FD) is the most important grapevine yellows, constituting a great threat in all major viticultural areas in Europe. The FD causal agent is an incidentally cited phytoplasma species termed ‘Candidatus Phytoplasma vitis’ (FDp), listed as a quarantine organism in Europe and mainly transmitted from vine to vine by the monophagous leafhopper Scaphoideus titanus. In the present study, the genetic variability of FDp identified in symptomatic plants located in a vineyard cv. Biancolella on the Ischia Island (Campania, Italy) was investigated. Our results unveiled for the first time the presence of FDp strains belonging to the subgroup 16SrV–C with a low genetic variability within map and rp genetic markers, reflecting an homogeneous genetic lineage of phytoplasma population examined in the present study. Phylogeny and nucleotide sequence analyses can also suggest the possible involvement of other insect vectors and plant hosts in the FD epidemiology on the Island. Further investigation to ascertain the presence of putative vectors and plant hosts representing inoculum sources should be carried out to reinforce the preliminary results obtained in the present study.

Dragon fruit (Selenicereus spp. syn. Hylocereus spp.) cultivation has grown significantly in recent years both in Brazil and throughout the world. This growth has demanded basic information on diseases caused by pathogens that can affect the crop. Among them, diseases of viral etiology stand out for the lack of curative control methods and for being underreported because the symptoms induced by viruses can be confounded with nutritional disorders. Previously, four viral species of the genus Potexvirus were detected in samples from different regions of Brazil. The objective of this study was to determine the incidence and spatial distribution of potexviruses in 12 commercial dragon fruit orchards in the south of Minas Gerais. The number of plants evaluated for incidence was calculated based on the size of each orchard, and the spatial distribution was investigated throughout the area. High incidences of potexviruses were detected, ranging from 80 to 100%. The spatial distribution of diseased plants showed an aggregated pattern in planting rows and a regular pattern in plots, indicating dissemination through cultural operations and infected seedlings as a source of inoculum. This was the first study on the epidemiology of viruses in dragon fruit orchards, and the data obtained indicate that producers are unaware of control measures required to manage the disease. In addition, the results showed the need to control seedling commercialization, aiming at the propagation of healthy material, along with the use of appropriate management practices to decrease the spread of viruses within orchards.

Pyricularia oryzae is the causative agent of rice blast disease that affects rice yield. The use of chemical fungicides in disease management has generated concern for the environment. In this work, we have developed four agaronanofungicides; chitosan-hexaconazole (CHEN), chitosan-dazomet (CDEN), chitosan-hexaconazole-dazomet (CHDEN), and chitosan agronanofungicide (CEN), and evaluated their antifungal efficacy against P. oryzae. The antifungal effect of the agronanofungicides was studied (in-vitro and in-vivo) by the poisoned media technique, and glasshouse trials. The agronanofungicides significantly inhibited the growth of P. oryzae suppressing the mycelial and conidial growth. The ultrastructural investigations have shown mycelial breakage and damage of the cell membrane in chitosan-based agronanofungicide-treated cells. The results for the efficacy under glasshouse conditions showed that CHDEN was the most promising agronanofungicide in managing rice blast with disease severity index (19.80%), lesion length (1.63 cm), AUDPC (390.60 unit²), disease reduction (80.20%), and a protection index of 82.26%. The least effective fungicide was commercial ANV with a disease severity index of 45.60%, lesion length (3.83 cm), AUDPC (1205.75 unit²), disease reduction (54.40%), and a protection index (45.24%). The treatments of agronanofungicides have increased the yield significantly with CHDEN having 239.00 and the control 113.67 grains per panicle. Based on the harvest index, the CHDEN agronanofungicide treatment had a higher value (0.56) which is significantly different (p ≤ 0.05) while the control had 0.47. This work reveals the strong antifungal effect of CHDEN against P. oryzae and its role in increasing the rice yield.