Journal of Plant Pathology最新文献

Both cucumber and melon are members of the Cucurbitaceae family and are important vegetable crops throughout the world. Among the most harmful oomycete species is downy mildew, which causes great damage to cucumber and melon production. An important basis for disease resistance molecular breeding is the study of genetic law and molecular regulation mechanism of cucumber and melon resistance to downy mildew. Pseudoperonospora cubensis is the pathogen responsible for downy mildew in cucumber and melon. Furthermore, there is a high degree of homology between the genomes of cucumber and melon. Cucumber and melon may therefore share a similar molecular genetic basis. This paper summarized and analyzed the physiological races differentiation of P. cubensis, the genetic law, and the mapping of resistance genes of cucumber and melon downy mildew resistance, to provide a reference for the comparative genomics research and the molecular design breeding of cucumber and melon downy mildew resistance.

Considerable losses of apple and peach tree seedlings were observed on 2012 in Tunisian nurseries and orchards. In the current study, surveys were conducted on apple and peach seedlings in ten and six nurseries respectively. Sampling was undertaken from symptomatic roots of seedlings showing various levels of decline. Isolation studies revealed the presence of Globisporangium ultimum (10.46% of apple seedlings and 18.96% of peach seedling), Phytopythium mercuriale (7.79% of apple and 22.29% of peach seedlings), and Phytopythium helicoides (5.8% of apple seedlings). On apple, a detached twig assay on the ‘Golden Delicious’ variety showed that P. mecuriale caused smaller necrotic lesions than G. ultimum and P. helicoides. A stem inoculation assay on the same variety supported the high virulence of G. ultimum which caused the death of seedlings. On the apple rootstock ‘MM106ʼ a soil inoculation assay supported the stem inoculation assay in that G. ultimum was the most virulent causing root rot and root weight reductions, followed by P. helicoides and P. mercuriale having the lowest virulence. On peach, a detached twigs essay on the ‘Carnival’ variety showed that G. ultimum and P. mercuriale caused necrotic lesions. A stem inoculation assay on both ‘Carnival’ and ‘Royal Glory’ varieties supported the virulence of these two oomycetes species which caused stem necrosis. On the peach rootstock ‘Garnem’ a soil inoculation assay showed that only G. ultimum was virulent causing root rot. These results suggest that these pathogens could function as potential decline inoculum sources that might limit post-plant tree growth in orchards.

The current work sought to characterize the secondary metabolites produced by endophytic fungi from the perennial grass Ischaemum ciliare Retz. and examine in-vitro and in-silico investigations on plant growth promotion. Cochliobolus fallax, Cochliobolus sp., Pestalotiopsis sp., Fusarium oxysporum, and Penicillium islandium were isolated from the aerial part of I. ciliare, and two endophytic fungi, Curvularia protuberata and Pestalotiopsis guepinii, were identified based on ITS rDNA sequence analysis. Furthermore, C. protuberata, F. oxysporum, and P. guepinii demonstrated high antagonistic activity against pathogenic fungal and bacterial strains. They showed significant plant growth promotion in the ethyl acetate extracts of C. protuberata and P. guepinii and the methanolic extract of I. ciliare on Capsicum annuum and Zea mays seedlings in vitro. OHR-LC MS analysis of P. guepinii ethyl acetate extract and I. ciliare methanolic extract identified ten and seventeen potential secondary metabolites, respectively. Furthermore, the docking analysis established the ligand-receptor interaction. It revealed that eight out of ten P. guepinii compounds and nine out of seventeen I. ciliare compounds have a strong binding affinity towards 3OGM, 4LDY, and 6KU3 target proteins. The endophytic fungal and host metabolite research in-vitro and in-silico aids in predicting compounds with bioactive principles, bio-control agents, and plant growth promoters.

Erwinia amylovora, the causative agent of fire blight of pome fruits and other rosaceous plants belongs to the group of regulated quarantine pests. The aim of this work was to characterize the populations of E. amylovora in Norway and their geographical distribution. A total of 238 E. amylovora isolates recovered from symptomatic host plants in Norway between 1986 and 2004 were genotyped by means of a short sequence repeat (SSR) marker (ATTACAGA) on plasmid pEa29. The SSR region was amplified and amplicon size determined using fluorescent labelling and rapid, automated capillary gel electrophoresis. All isolates contained the pEa29 plasmid harbouring the investigated marker. In total, ten genotypes were identified, of which two were detected only once. The number of repeats varied from 3 to 13, with 43% of the isolates containing five repeats. Of 17 isolates collected between 1986 and 1991, all but one contained five repeats, whereas more variation was observed in isolates from the period 2000 to 2004. Most of the isolates (80%) originated from Cotoneaster bullatus, hence no relationship between genotype of the isolate and host species that it was isolated from could be detected. This historic data suggests multiple introductions of E. amylovora to Norway.

Abstract

Hevea brasiliensis (Para rubber tree) is a commercially cultivated crop for latex production worldwide. Rubber trees from Southern states of India have been affected by Circular Leaf Spot (CLS) disease caused by Colletotrichum fructicola and Colletotrichum siamense causing yellowing and severe defoliation in rubber plantations in recent years. In this study, we collected infected leaf samples of CLS disease from different locations in the South Indian states of Kerala, Tamil Nadu, and Karnataka. Colletotrichum fructicola and C. siamense were identified as the causative agents of CLS disease and the isolate, C. fructicola was used for genomics analysis. We performed whole-genome sequencing (WGS) of, C. fructicola and carried out gene content analysis by comparing it with other reported Colletotrichum species. In silico analysis revealed a rich repertoire of pathogenicity genes and CAZymes in C. fructicola encoding secreted proteins, effectors, plant cell wall degrading enzymes, and secondary metabolism-associated proteins with possible roles in the host-specific interaction and pathogenicity. Our dataset provides a rich resource for understanding the pathogenicity-related genes that are involved in CLS disease progression and gives a basis for subsequent functional genomics research in C. fructicola.

Due to substantial legal and regulatory constraints, as well as the hazards they pose to human health and the environment, the use of synthetic pesticides to control plant diseases is rapidly declining. Furthermore, the increasing need for alternative crop protection techniques is being driven by disease strains that have developed resistance. Being a source of bioactive molecules, natural compounds may offer a more consumer- and environmentally friendly alternative to pesticides by reducing their application. We attempt to present a number of scientific studies in this Opinion piece that show how pomegranate (Punica granatum L.) peel (PP) can prevent and manage a number of diseases that affect significant pre- and post-harvest crops, both when used alone and in combination.

Verticillium dahliae Kleb., the causal agent of Verticillium wilts, is a devastating plant disease affecting many plant species. Fungus V. dahliae was detected in a partially artificially established Acer pseudoplatanus L. forest stand in central Slovenia. This finding incited further study about the risk of different sources of V. dahliae isolates for maples in forests and the pathogenicity of three V. dahliae isolates of different origins was tested on saplings of A. pseudoplatanus, A. platanoides L., and A. campestre L. The inoculated saplings exhibited disease symptoms, i.e., leaf necrosis and wilting. At the end of the pathogenicity test, typical xylem browning was visible on the cross-sections, and the pathogen was successfully re-isolated. The isolates showed significant differences in their pathogenicity to specific maple hosts, with the agricultural isolate (originated from bell pepper) being the most aggressive on all three maple species. The disease severity index (DSI) and relative area under the disease progress curve (rAUDPC), as well as the success of re-isolation, indicate that A. platanoides is the most susceptible to inoculation with V. dahliae. In addition, significant differences in sapling biomass were observed between treated and control plants. These results suggest that maples in forest stands are threatened by V. dahliae, and biosecurity measures should be considered and implemented in forest management to reduce the transmission and potential spread of the pathogen.

The polyphagous shot hole borer beetle (PSHB, Euwallacea fornicatus) is a pest of global significance. PSHB is an ambrosia beetle which, together with its mutualistic fungi (including Fusarium euwallaceae), can cause the death of more than 100 tree species in invaded ranges. Management of PSHB mostly relies on the removal of infested plant material. Chemical control options have been investigated only in the USA and Israel and only on a few tree species. This study evaluated four chemical treatments for the therapeutic control of PSHB on American sweetgum (Liquidambar styraciflua) in South Africa (1) bifenthrin + surfactant (alcohol ethoxylate), (2) cypermethrin + surfactant (vitamin E) + salicylic acid, (3) emamectin benzoate, and (4) propiconazole. Trees were inoculated with F. euwallaceae and mature PSHB females using a novel technique to document fungal lesion development and PSHB colony establishment success. The bifenthrin and cypermethrin treatments reduced additional PSHB colonisation attempts on treated trees by ca. 40%, while the other treatments had no effect. Colony establishment success was reduced in all treatments by between 20 and 40%. Fungal growth was inhibited only after the application of propiconazole by ca. 36%. Gallery length and the number of PSHB individuals in successful colonies were unaffected by any of the chemical treatments. These results indicate that chemical control of PSHB is only partially effective. Successful PSHB management will likely depend on a combination of chemical control options and other control strategies in an integrated pest management program.

Cucumber Fusarium wilt caused by Fusarium oxysporum is a serious soil-borne disease, which seriously affects the yield of cucumber. When plant roots are subjected to invasion by pathogenic bacteria, endophytic microbial communities also change greatly. Screening for Fusarium wilt antagonistic bacteria has generally focused on screening for antagonistic strains from healthy plants, with few reports of screening for antagonists from leaves of diseased plants. In this study, the leaves of cucumber plants infected with Fusarium wilt disease were used for the isolation of antagonists and a total of four endophytes with obvious antagonistic effects were screened. 16S rDNA gene sequencing confirmed that the four strains belonged to Paenibacillus polymyxa (Y-4, Y-6, Y-14) and Bacillus zanthoxyli (Y-9), and that all antagonistic strains exhibited the ability to produce amylase, pectinase and hydrogen peroxide (H₂O₂). In the pot experiment, four antagonistic strains all could significantly reduce the disease index of cucumber Fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum Owen (FOC) and promote root growth. Furthermore, the cucumber plants with antagonistic bacteria treatment possessed higher photosynthetic pigment content, antioxidant capacity, proline content and root vigor. These results indicated the leaves of cucumber diseased strain may also be a potential source for screening novel antagonistic agents against cucumber Fusarium wilt.

Abstract

The persistence and progression of Erwinia amylovora in naturally infected orchards is still not fully understood and the majority of studies have been carried out under controlled or artificial infections. A major hurdle stems from the inability to characterize the viability of the bacterium in its natural state. Most standard tests, including real-time qPCR, fail to differentiate live from dead cells, while culture dependent methods lack sensitivity. Even in orchards with recurring infections, the detection of E. amylovora is erratic. Immuno-flow cytometry (IFCM) is considered a high throughput tool in clinics and food industry but has been rarely used as diagnostic test for plant pathogens. Two pear orchards with fire blight history, located in the central part of Portugal, were selected for epidemiological monitoring between February and June, from 2019 to 2022. A total of 440 samples were tested using EPPO standard diagnostic protocols. To address the epidemiological behaviour of E. amylovora, we devised an IFCM test using specific monoclonal antibodies and viability dyes, validated in a subset of 149 samples, testing positive in routine diagnostic tests. Our IFCM test was able to differentiate live and dead E. amylovora in naturally infected samples with concentrations as low as 3.54 × 10⁴ cell·mL⁻¹, confirming positive results for 91% these samples, while 19.4% were considered positive by isolation, 38% using conventional PCR and 95% for real-time qPCR. Temporal analysis showed the highest number of positive samples regardless of the method employed in April, May and June, while viability values measured with IFCM were the highest in April, coinciding with the exit of dormancy and early flowering of pear trees. Integrative analysis of E. amylovora viability and population dynamics over the growing season allowed identification of distinct outbreak risks associated with these Portuguese pear orchards.