Journal of Plant Pathology最新文献

The carnation (Dianthus caryophyllus L.) stands as a key export important for Colombia, yet its production faces challenges due to vascular wilting triggered by Fusarium oxysporum f. sp. dianthi (Fod). This study examined Fod impact on stomatal resistance, leaf temperature, and dry biomass in carnation plants, alongside its influence on rooted cuttings of two carnation cultivars differing in susceptibility to vascular wilting. Employing a completely randomized design, the resistant cultivar ‘Golem’ and susceptible cultivar ‘Mizuki’, each with four weeks of rooting, were inoculated with Fod, while controls were maintained. Both cultivars exhibited altered leaf temperatures and AUDPC (Area Under Disease Progression Curve) parameters post-inoculation, compared to their controls, indicating leaf temperature’s potential as an early Fod presence indicator. The effects of inoculation with Fod for each cultivar were different for stomatal resistance, associated with the asymptomatic stage of the disease. These findings suggest that the resistant cultivar activates early stomatal closure mechanisms, possibly through hormonal pathways, enhancing its ability to combat the pathogen. Real-time PCR analysis of rga1 and mlp43-like genes indicated the involvement of Abscisic Acid (ABA) and Salicylic Acid (SA) hormonal pathways in cultivar-specific responses post-inoculation, even at early stages. These results highlighted Fod presence before symptom development and their significance for devising early detection strategies and breeding genetically resistant cultivars. This study underscores the intricate interplay between plant-pathogen interactions and hormonal signaling pathways, providing valuable insights for effective disease management and cultivar development in carnation production.

Bacterial wilt caused by strains of the Ralstonia solanacearum species complex is a severe disease affecting plants. The type III secretion system delivers type III effectors (T3Es) from the pathogen to the host plant and is one of the main virulence determinants of R. solanacearum strains. However, the functions of most T3Es, including the R. solanacearum effectors RipAX1 and RipAX2, are not completely understood. In this study, we determined that RipAX1 and RipAX2 share a potential but highly conserved M91 metalloenzyme structural domain. Heterologous overexpression of RipAX1 or RipAX2 neither caused nor inhibited the hypersensitive response (HR) of plant tissues, and their expression in Saccharomyces cerevisiae did not inhibit yeast growth. RipAX1 and RipAX2 localized to the cytoplasm of Nicotiana benthamiana leaf epidermal cells and Arabidopsis thaliana protoplasts. The two effectors interacted with specific members of the plant mitogen-activated protein kinase (MAPK) family. However, RipAX1 and RipAX2 did not directly cleave MAPKs, despite their predicted metalloenzyme activity, although RipAX1 inhibited the phosphorylation of plant MAPKs. These results elucidate a novel aspect of the molecular mechanism underlying the repression of host immunity by T3Es from R. solanacearum species complex strains.

Erwinia pyrifoliae, the Gram-negative bacterial pathogen responsible for black shoot blight, exhibits symptoms similar to E. amylovora (fire blight), though with distinct molecular characteristics. Given its prevalence primarily in South Korea and the availability of only nine assembled genomes, there is a lack of high-quality genome sequences and annotated genetic information for E. pyrifoliae. We present the sequencing and assembly of a Korean E. pyrifoliae strain, YKB12327, isolated from a diseased apple tree branch, using a combination of long Oxford Nanopore Technologies and short Illumina sequence reads. This genome comprises a circular chromosome and three plasmid sequences, totaling 4,061,634 bp. Annotation of YKB12327 identifies 3123 coding sequence protein-coding genes, 22 rRNA genes (5S, 16S, and 23S), and 76 tRNA genes. Our sequence data will enrich the current E. pyrifoliae genome resources and facilitate in understanding its evolution, diversity and structural variations, as well as the molecular basis of pathogenesis.

Plasmopara viticola (Berk. & M. A. Curtis) Berl. & De Toni, the causal agent of downy mildew, affects both cultivated and wild grapevine. Wild species of the genus Vitis L. are reliable sources of resistance to many of the diseases that affect cultivated grapevines. For this reason, it is important to study wildly growing (typical wild and feral) accessions belonging to V. vinifera L. The aim of this research was to study the levels of resistance to P. viticola of 57 Georgian wildly growing grapevine accessions by leaf disc method. The data were collected over eight years, from 2014 to 2021. Different degrees of resistance have been detected, ranging from susceptible (8.8% of accessions), low resistance (8.8% of accessions) moderate resistance (22.8%), and resistance (12.3% of accessions). Resistance of the 33,3% of the tested accessions was unstable and varied from susceptible to resistance across the years. Among resistant wildly growing grapevine genotypes, there are several accessions with a high density of the trichomes, although the data showed that the density of prostrate and erect hairs of the leaves is not correlated with the resistance trait. A large number of resistant genotypes among wildly growing grapevines suggests that in its natural habitat more resistant forms to downy mildew survives in the process of natural selection. Further studies are needed to characterize the plant-pathogen interaction and the mechanism of resistance of the wild accessions, although the resistant accessions, such as Tedotsminda 07, Tedotsminda 09, Tedotsimda 10 can be interesting for the breeding purposes in the future.

Grape downy mildew, caused by the oomycete Plasmopara viticola, is a major threat to Vitis vinifera grape production. Several breeding programs rely on resistance factors (Rpvs) from American and Asian Vitis species to confer resistance to P. viticola. Although the use of these crossing hybrids offers a promising strategy for disease control, variants capable of overcoming host resistance are emerging. A thorough characterization of these isolates is needed to define new strategies for breeding programs. The investigation of varying aggressiveness of two P. viticola pathotypes was investigated. One pathotype is unable to overcome Rpv3.1 based resistance and another pathotype was isolated from a grapevine carrying the Rpv3.1 locus. Their aggressiveness was evaluated on five grapevine genotypes harboring distinct combinations of Rpv loci. Macroscopic and microscopic development of the pathogen was characterised throughout its colonization of grapevine leaves. Our findings demonstrate that the P. viticola isolate NW-10/16 is not only capable of overcoming Rpv3-based resistance but also exhibited a faster growth, increased sporulation, and a denser mycelial colonization within the plant mesophyll when compared with the avRpv3 + isolate in susceptible plants. The identification and characterization of new, more aggressive, P. viticola pathotypes is crucial to promote durable management of the resistant grapevine hybrids and to mitigate the threat of downy mildew.

The pathogenic watermelon mosaic virus (WMV) causes severe crop losses and threatens cucurbits production worldwide. This study presents the first sequenced genome of WMV from Iraq and the second from Iran. The near-complete genome sequences of Iranian (In) and Iraqi (Iq) isolates were, respectively, 9999 and 10,041 nucleotides in length, excluding the 3′-terminal poly(A) tail. WMV-Iq and WMV-In shared nucleotide identities of 92.61–96.32% with those of 30 worldwide representative WMV isolates in GenBank and identities of 93.04–93.90% with a previously reported Iranian isolate IR02-54. Phylogenetic analysis based on the genomic sequences clustered all 32 isolates into seven groups (G1–G7), in which WMV-Iq and WMV-In clustered alongside 12 isolates from Asia, Europe, and America in group G1. Phylogenetic analysis of nucleotide sequences of the coat protein gene of WMV isolates resolved into five phylogroups (I–V) and both isolates, WMV-Iq and WMV-In, clustered together with isolates in group I and contain the N-terminal KEA motif, which is the characteristic of group I isolates. Our results show that WMV-Iq and WMV-In are recombinant isolates with multiple recombination events detected across the genome. Symptom intensity of WMV isolates in experimental hosts was variable and depended upon the host species, virulence of isolates, and environmental conditions.

Fire blight is a devastating disease of apple and pear worldwide. One reason fire blight is so difficult to manage is because of the lack of effective non-antibiotic management options as well as a limited host resistance gene pool. Traditional management approaches utilizing antibiotic and copper sprays face multiple problems including antibiotic resistance and human health concerns. Furthermore, most management materials are used to control the blossom blight stage of infection, and fewer materials are available to control shoot blight stage of infection. Breeding for host resistance against fire blight is limited by the heterozygosity of apple, as well as the lack of understanding of the host-pathogen interactions. In this review, we raised some of these “burning questions”, which suggest directions for future research in management and resistance breeding of fire blight.

Ralstonia solanacearum and R. pseudosolanacearum are well-known bacterial plant pathogens that cause significant losses to both ornamental and agricultural plants. It has been suggested that they are not the primary cause of bacterial wilt in Eucalyptus species, but rather are opportunistic, taking advantage of trees predisposed to infection by abiotic and biotic factors. To test this hypothesis, the bacterial community within the vascular tissue of asymptomatic Eucalyptus grandis x E. urophylla trees, and those displaying varying stages of infection in China and Indonesia were compared using 16S rRNA profiling. Asymptomatic trees growing in areas where bacterial infections had never previously been reported to occur were included as controls. Ralstonia species were found within the vascular tissue of both asymptomatic and symptomatic trees, in high abundance. In the control samples, bacterial diversity within the vascular tissue was high with a low abundance of Ralstonia species. The presence of Ralstonia species in asymptomatic and control samples supports the hypothesis that these species are latent and/or opportunistic pathogens in E. grandis x E. urophylla trees.