European Journal of Plant Pathology最新文献

Plum pox virus (PPV, genus Potyvirus) is one of the most economically important plant viruses. The PPV M strain (PPV-M) was first isolated in Japan in 2016. While a broad host range of the PPV M strain from trees to weeds has been widely reported, host range and the contribution of weeds to the PPV infection cycle in Japan remained unknown. In this study, we examined the host range of PPV-M in Japan within the Asteraceae weeds and explored its potential role as an intermediate host. By mechanically inoculating twelve herbaceous species belonging to Asteraceae (alternatively Compositae) in orchards with PPV-M, we found that all were susceptible to the virus. Of those, Hemisteptia lyrata showed high infection rates on the upper leaves, typically favored by aphids. A subsequent survey of multiple aphid species feeding on H. lyrata showed a seasonal infection cycle in which the aphid Aphis fabae solanella likely transmitted PPV-M from Japanese apricot leaves to H. lyrata in the spring. Then, A. spiraecola, an efficient PPV vector known to shift between hosts in summer and autumn, transmitted the disease to healthy Japanese apricot seedlings from PPV-M infected H. lyrata in autumn. It is conceivable that PPV-M in Japanese apricot orchards follows a seasonal infection cycle, potentially involving an intermediate host (Asteraceae) and two aphid species.

Cronartium pini and C. ribicola are rust fungi that cause destructive diseases of pines (Pinus spp.). These rusts spread via alternate hosts, among which Melampyrum spp., Veronica spp. and Impatiens spp. are important for C. pini and Ribes spp. for C. ribicola. Congeneric alternate hosts vary in their susceptibility to Cronartium rusts, but the reasons for this variation are not clear. To clarify whether internal, endophytic fungi could explain these differences, we investigated the temporal and spatial variation in fungal endophyte composition of C. pini-resistant M. pratense, V. chamaedrys and I. glandulifera, C. pini-susceptible M. sylvaticum, V. longifolia and I. balsamina, C. ribicola-resistant R. rubrum and C. ribicola-susceptible R. nigrum. In total, 2695 fungal endophytic isolates were obtained and classified into 37 morphotypes, with 1373 cultures isolated in early summer and 1322 in late summer. Fifty-two isolates were identified to species or genus level. The most common morphotypes were identified as Heterophoma sp. Some variation in the abundance of morphotypes occurred between collection sites, but the same morphotypes dominated across the sites and species. The diversity of morphotypes was higher in early September than in late June in all species and the same morphotypes dominated in both early and late season. The diversity of fungal endophytes was higher in resistant Veronica and Ribes than in susceptible congeneric species, but the results suggest that the diversity or abundance of culturable fungal endophytes does not explain the differences in the congeneric species’ susceptibility to rust fungi.

Plasmodiophora brassicae is a serious threat to Brassica crops worldwide, resulting in substantial economic losses for growers. Biocontrol with chitinolytic bacteria producing chitinase is gaining attention as a natural alternative to chemicals. This approach is favored due to the essential role chitinases play in protecting against chitin-containing pathogens. Given that chitin is a major component in the resting spores of P. brassicae and plays a crucial role during pathogenesis, it is probable that Paenibacillus chitinolyticus, producing a high level of chitinase, could suppress P. brassicae by targeting chitin in a critical stage of this pathogen’s life cycle. Our research aimed to evaluate the effect of various applications of P. chitinolyticus on clubroot suppression in two economically important Brassica species: Chinese cabbage and rapeseed. The effectiveness of the cell-free supernatant (CFS) of an endemic strain of P. chitinolyticus from the Czech Republic at five different time points was studied in the greenhouse by measuring the disease severity index. Early application of P. chitinolyticus decreased the disease index significantly within both plant species resulting in increased shoot dry weight. In conclusion, the CFS of P.chitinolyticus has significant antagonistic activity against clubroot in Chinese cabbage and rapeseed in the early developmental stages of clubroot occurrence and holds the potential as a biofertilizer as well as bioprotectant agent in clubroot management of P. brassicae.

Brazil is the world's largest producer and exporter of soybean and studies show that production will continue to grow in the coming years. However, this increase is considered a major challenge due to the serious damage and losses caused by nematodes. The use of resistant materials presents a sustainable alternative for suppressing them. Therefore, the objective was to evaluate the reaction of soybean genotypes to populations of Meloidogyne incognita and M. javanica. Two experiments were carried out for each species, on different dates, under greenhouse conditions, in a randomized block design with ten and twenty-two treatments, respectively, and four replicates. Plants were inoculated ten days after planting with a suspension of 2500 eggs and second-stage juveniles of M. incognita and M. javanica. Evaluations took place sixty days after inoculation (DAI), determining plant height, stem diameter, Spad index, leaf area index, reproduction factor and reproduction factor reduction. For the species M. incognita all genotypes were susceptible. The UFUL 592 and UFUL 298 genotypes had greater vegetative development and the UFUL 526 genotype behaved as a good host for the nematode. For M. javanica, the UFUL 172 and UFUL 592 genotypes showed good performance in terms of growth parameters, as well as nematological ones. In general, the UFUL 592 genotype performed well in the four trials.

This study investigated the effectiveness of two plant growth-promoting rhizobacteria (PGPR) formulations, Bio Arc^® 6% WP (BA, Bacillus megaterium) and BECTO Grow Roots^® (BGR; Serratia marcescens, Pseudomonas putida, and P. fluorescens). Additionally, it focused on naturally infested soil that had undergone metam potassium fumigation to reduce root-knot nematode (RKN), specifically Meloidogyne incognita. It aimed to monitor eggplant response to soil biodiversity changes for 60 days of the experiment under greenhouse conditions. Our data showed that soil fumigation eliminated nematodes and reduced other microorganisms significantly. In sterilized soil, plant fresh root weight significantly decreased after the elimination of soil biota. Moreover, BGR achieved the highest plant growth vigor [fresh root (18.48%), fresh shoot (23.52%), and fresh plant weight (21.03%)], followed by BA [fresh root (11.98%), fresh shoot (20.77%), and fresh plant weight (16.38%), respectively]. Plant growth traits increased significantly following the second reinoculation of PGPR after a month. Also, the same data trend was observed in treatments inoculated with RKN + PGPR. Furthermore, BGR treatments exhibited consistent efficacy in controlling nematode infection, maintaining superior vegetative growth compared to BA treatments over time. However, BA treatments displayed a decline in plant growth when faced with repeated nematode infection. The range of gall, egg mass, and second-stage juvenile (J2s) numbers diminished after inoculation-infected plants with RKN and PGPR compared with infected plants alone. Biochemical changes in eggplant roots cultivated in sterilized soil exposed significant enhancement in total sugars, protein, and nonenzymatic antioxidants (flavonoids and phenolic content), with antioxidant activity enhanced upon inoculation of PGPR and RKN. Oppositely, the levels of enzymatic antioxidants (catalase, peroxidase, and superoxide dismutase) decreased significantly with single and double PGPR application. However, the decline was less pronounced in the BGR treatments than in BA. In contradiction of oxidative enzymes, reinoculated PGPR + RKN multiplied significantly in reinfested RKN treatments. Our findings support the use of PGPR combinations, in particular, for preventive inoculation against M. incognita. They also enhance plant growth-promoting factors and stimulate plant defenses against inevitable soil reinfestation following soil fumigation.

Thailand, the leading producer of rubber, is currently grappling with Corynespora leaf fall disease, a condition caused by Corynespora cassiicola (Berk. & Curt.) Wei., leading to defoliation and significant yield losses. In this context, 74 endophytic Trichoderma strains isolated from the foliage of healthy rubber trees were assessed for their antagonistic capabilities against C. cassiicola under controlled laboratory conditions. Specifically, isolates of T. atroviride (1 strain), T. asperellum (4 strains), T. hamatum (4 strains), T. harzianum (4 strains), and T. viride (2 strains) were identified based on their pronounced antagonistic potential, as determined through detached leaf and dual culture assays. These isolates were further evaluated for their disease control efficacy under greenhouse conditions. Among the evaluated Trichoderma strains, T. harzianum KUFA 0760 was observed to exhibit significant antagonistic effects in mitigating Corynespora leaf fall disease, achieving a 49.27% reduction in disease incidence tested by the detached leaf method. This was closely followed by T. asperellum KUFA 0754 and T. harzianum KUFA 0762, which suppressed disease severity by 44% and 45%, respectively. These findings warranted the selection of these strains for subsequent determination of their biocontrol efficacy against the disease under field conditions. In these trials, T. harzianum KUFA 0762 emerged as the most effective, leading to a 36–40% reduction in disease prevalence, while T. harzianum KUFA 0760 achieved a 27% reduction in disease severity. Contrastingly, the application of carbendazim was found to have the highest efficacy, resulting in a 57–59% decrease in disease incidence. Additionally, all tested Trichoderma strains demonstrated compatibility with the recommended fungicide for this disease, mancozeb, at a concentration of 3000 ppm. The outcomes of this investigation underscore the significant biocontrol potential of endophytic Trichoderma spp. against rubber tree diseases. The results advocate for the utilization of such biocontrol agents as either standalone alternatives to chemical fungicides or as part of an integrated pest management strategy, in combination with fungicidal treatments, for the effective control of Corynespora leaf fall disease.

Dragon fruit canker (DFC) disease caused by the fungus Neoscytalidium dimidiatum poses a significant threat to yield and fruit quality in cultivating dragon fruit (Hylocereus spp.). Accurate assessment of canker severity is crucial for determining the effectiveness of management strategies for controlling this disease. We developed a standard area diagram set (SADs) consisting of nine levels of disease severity (0.5 to 60%) and subsequently validated the SADs based on the patterns and distribution of the symptoms. For the validation, eighteen raters with no prior experience in disease assessment were recruited to estimate the severity of canker symptoms on 50 stems/cladodes of dragon fruit before and after using SADs. Both accuracy and precision were improved when they used the SADs. Statistical parameters for the 18 raters were as follows: bias coefficient factor (C_b) without SADs = 0.791, with SADs = 0.982; correlation coefficient (r) without SADs = 0.884, with SADs = 0.918; Lin's concordance correlation coefficient (ρ_c) without SADs = 0.702, with SADs = 0.902. Estimates were also more reliable by using the SADs: inter-rater coefficient of determination (R²) without SADs = 0.749, with SADs = 0.810. The newly developed SADs provide a practical, standardized tool for assessing dragon fruit canker severity, aiding researchers and growers in more accurate disease monitoring, yield loss estimation, intervention planning, and control measure evaluation.

Root-knot nematodes (RKNs), including Meloidogyne spp., are renowned as one of the most destructive plant-parasites worldwide. The culture filtrates of entomopathogenic fungi (EPF), obtained through fermentation processes and containing significant enzyme and toxins, exhibit nematicidal activity. Moreover, the host specificity of EPF is notable, with significant variations in host spectrum and virulence among different strains. Thus, screening indigenous EPF against RKNs will broaden the resource base for developing biological control pesticides. In this study, we isolated 25 EPF strains through the Galleria bait method and investigated the pathogenicity against RKNs. Amongst the 25 EPF strains, which were molecularly identified as Beauveria spp., Metarhizium spp., Purpureocillium spp., and Cordyceps spp., several exhibited promising control effects on RKNs. Three EPF culture filters (B. bassiana 25, P. lilacinum 26, and M. pinghaeuse 39) exhibited nematicidal activity that was not affected by illumination methods or temperature. This research indicates the potential of B. bassiana 25, P. lilacinum 26, and M. pinghaeuse 39 as biological agents against RKNs.

Hop cultivation, integral to the brewing industry, faces challenges from viroids, especially the citrus bark cracking viroid (CBCVd) but also the hop latent viroid (HLVd) influences hop cone quality. We focused on the degradation kinetics of HLVd thereby covering compost, silage, and digestate made from hop residues. In this study, HLVd serves as a model for understanding CBCVd, which causes significant stunting and yield losses in European hop crops. Composting experiments revealed that although composting significantly lowers HLVd levels, complete degradation within 7 weeks is not guaranteed, with loose compost showing a more rapid reduction than compacted variants. Infectivity experiments conducted using inocula obtained from HLVd-infected hop plant residues exposed to composting, ensiling, and biogas digestate did not result in the transmission of HLVd to viroid-free plants. Also extracting and analyzing the soil-root mixture of plants inoculated with HLVd-infected hop residues did not show evidence for viroid persistence. Degradation experiments further differentiated between the physiochemical and biological influences on viroid and viroid-like random RNA stability, showing that higher temperatures of 50 °C enhance degradation over 40 °C, and pH levels of 5 or 7 are slowing degradation. In contrast deionized water or a pH of 4 or 9 enhances viroid degradation. Adding extracts from digestate accelerated the process indicating a role of biological activity. Interestingly, a viroid-like random RNA with similar physiochemical properties, showed to degrade faster compared to HLVd, suggesting high robustness of the actual viroid secondary structure. These findings offer valuable insights into managing HLVd in hops and potentially other crops, highlighting effective strategies to mitigate viroid spread, and contributing to broader understanding of RNA degradation in agriculture.

A nematological survey was conducted between 2021 and 2022 in banana fields distributed in two major banana-producing regions in the western coast of Syria. As a result, six populations of Xiphinema spp. identified as X. diffusum, X. pachtaicum, X. simile, X. vuittenezi and X. zagrosense were isolated from the rhizosphere of banana plants (Musa sp.) and characterized using morphological and molecular data based on two rRNA genes (D2–D3 expansion segments of the 28S, and ITS fragments) and partial region of the cytochrome oxidase I gene (COI mtDNA) sequences. Moreover, the molecular identification of the endosymbionts of these populations was also performed using the complete 16S rDNA gene. The phylogenetic relationships of the recovered species of nematodes and respective endosymbionts were reconstructed. Candidatus Xiphinematobacter sp. (OR196969; OR196971) and Ca. Xiphinematobacter sp. (OR196970) were detected in X. diffusum and X. simile, respectively, and clustered together with other Ca. Xiphinematobacter sp.A and sp.I respectively. To our knowledge, this is the first report of X. diffusum, X. simile, X. vuittenezi and X. zagrosense parasitizing banana in Syria, extending the geographical distribution of these species within the Mediterranean Basin.