Journal of General Plant Pathology最新文献

Necrotic lesions were found on the leaves and stems of Japanese white oak (Quercus myrsinifolia) seedlings on a nature trail in Japan. A species of Phytophthora was isolated from the necrotic lesions and adjacent soil. Molecular phylogenetic analysis and morphological examination revealed it to be Phytophthora castaneae, known as a causal pathogen of trunk rot on chestnuts. Pathogenicity testing showed that P. castaneae caused leaf blight on previously healthy Japanese white oak seedlings. In addition, using a soil infestation method, we confirmed that it was also pathogenic to chestnut seedlings, but the roots of Japanese white oak were not infected. This is the first report of P. castaneae causing disease in a natural ecosystem in Japan.

Transcription factors belonging to the family of ethylene response factors (ERFs) in plants function in disease resistance to pathogens. One of the tobacco ERF genes, NtERF5, inhibits the accumulation of tobacco mosaic virus (genus Tobamovirus) when overexpressed in tobacco carrying the resistance gene N. Here, we report that NtERF5 can function as a transcriptional activator through binding of the GCC-box in planta. We then determined whether overexpression of NtERF5 in tobacco lacking the N gene (nn tobacco) inhibited infection by potato virus X (PVX: genus Potexvirus). Transient overexpression of NtERF5 inhibited the accumulation of PVX without affecting virus spread and increased the transcript levels of NtPRB-1b and NtPR6, which are jasmonic acid/ethylene-signaling marker genes encoding pathogenesis-related (PR) proteins. Stable overexpression of NtERF5 in nn tobacco also resulted in decreased PVX accumulation and the induction of the expression of NtPRB-1b and NtPR6. Our results revealed that overexpression of NtERF5 limited successful infection and accumulation of PVX, suggesting the role of NtERF5 as a positive regulator of basal defense against virus infection.

Abstract

Root rot of hydroponically grown Welsh onion has caused considerable economic losses every year since commercial cultivation began in 1988 in Hiroshima Prefecture, Japan. The primary pathogens, which have not been reported to form sexual structures, are Pythium spp. including Pythium clusters B2a sp., which is most prevalent, and B1d sp. and Pythium clade A sp. These pathogens infect Welsh onion roots by producing sporangia and zoospores. The objective of this study was to elucidate the inhibitory effects of low-pH solutions on root-rot pathogens of hydroponically grown Welsh onion. Naturally occurring disease was significantly lower after treatment with nutrient solutions with a pH maintained at 4.3–4.9 than with conventional unmanaged solutions (pH 5.4–6.4). In a greenhouse after inoculation of infected Welsh onion with Pythium cluster B2a sp., low-pH solutions (pH 4.0 and 4.5) significantly suppressed zoospore production and reduced the percentage of root infections compared to the conventional solution (pH 5.5). In other greenhouse inoculation tests with Pythium clusters B2a sp. and B1d sp. and Pythium clade A sp., the low-pH solution (pH 4.0) substantially decreased zoospore density and root infection compared to the conventional solution (pH 5.5). The low-pH solutions did not negatively impact crop yield in the greenhouse tests and thus can be used to suppress root rot in hydroponically grown Welsh onions.

The control of kiwifruit canker, caused by Pseudomonas syringae pv. actinidiae (Psa), largely relies on copper pesticides. After epidemics of kiwifruit canker in Ehime Prefecture, Japan, we comprehensively surveyed isolates of Psa biovars 1 (Psa 1) and 3 (Psa 3) for copper resistance from 2002 to 2019. In Psa 1, copper-resistant isolates drastically increased in 2006 and onward during the survey from 2002 to 2008 and were frequently found in 2017. By contrast, copper-resistant Psa 3 isolates emerged soon after its first identification in 2014 and spread to different orchards with an isolation ratio of about 10%. Identification of copper resistance-related genes by whole-genome resequencing revealed that cop genes from Psa 1 isolates in 2017 were almost identical to those from Psa 1 isolates from the late 1980s. On the contrary, in Psa 3 isolates, we found two different sets of cop genes. One of them was closely related to those from other Pseudomonas species, and the other to those from P. syringae pv. tomato. Notably, copper-sensitive Psa1 and 3 isolates had copAB and copRS homologs but no homologs of copCD. Despite the diversity in cop gene sequences, PCR detection of copCD sequences from different lineages matched perfectly with their copper resistance.

Colletotrichum scovillei, a member of the Colletotrichum acutatum species complex, causes severe anthracnose of pepper fruit, reducing yield and quality. However, the molecular mechanisms underlying its pathogenesis are unknown. Ste7 kinase in the Fus3/Kss1-related mitogen protein kinase signaling pathway plays an important role in plant infection by phytopathogenic fungi. In this study, the function of CsSTE7, an ortholog of Ste7, was investigated in C. scovillei using a targeted gene deletion mutant (ΔCsste7). Compared to the wild type, ΔCsste7 had normal mycelial growth, but conidial morphology, germination of conidia, and tolerance to cell wall integrity and osmotic stresses were defective. Importantly, ΔCsste7 was completely defective in appressorium formation and causing anthracnose on pepper fruits. These defects were restored in the complemented strain (Csste7c). The results suggest that CsSTE7 is essential for development and pathogenicity of C. scovillei.

Abstract

Species of Colletotrichum are common pathogens that cause loquat fruit rot in Nagasaki Prefecture, Japan. For clarifying the site of infection and the Colletotrichum species responsible for anthracnose in loquat trees, fungi were isolated from asymptomatic flowers and rotten fruits and identified to the species rank based on morphological and molecular phylogenetic analyses. Nineteen isolates from 148 rotten fruits were identified as C. fioriniae (12 isolates), C. nymphaeae (2 isolates), C. gloeosporioides s. s. (1 isolate), and four unidentified species of Colletotrichum. From 900 asymptomatic flowers, C. fioriniae (5 isolates), C. gloeosporioides s. s. (1 isolate), C. siamense (2 isolates), an unknown species (11 isolates) belonging to the C. acutatum species complex, and 2 were Colletotrichum spp. All isolates were pathogenic on wounded leaves and fruits. These results imply that C. fioriniae and C. gloeosporioides s. s. infect flowers and cause loquat fruit rot after maturation. However, the pathogenicity of the other species remains unclear as does the reason for the differences in the composition and proportions of fungal species in fruits and flowers. Eleven isolates obtained from asymptomatic flowers that also cause anthracnose disease in loquat were identified as a novel species of Colletotrichum, which was named C. nagasakiense sp. nov.

Wheat blast is an important disease that affects cross-border food security. The causal pathogen, Pyricularia oryzae (syn. Magnaporthe oryzae) Triticum pathotype (MoT), forms a phylogenetic group distinct from the other P. oryzae pathotypes pathogenic on various gramineous plants. Here we developed MoT-specific primer sets for qPCR and LAMP detection methods, and their amplification specificity and efficiency were tested in comparison with previous reported MoT-specific primers. The amplification efficiency and specificity were affected by the polymerase premix. To evaluate the detection specificity, purified DNA samples of 15 MoT isolates, 89 non-MoT isolates of Pyricularia spp., and crude DNA from wheat plants inoculated with MoT were used. We conclude that the Sp3 primer sets for qPCR and the MoT3L primer sets for LAMP were the best in this research.

During harvest in August 2017, wilting lettuces with crown rot were observed in Kagawa Prefecture, Japan. Fungi with aseptate hyphae were isolated from the rotted crowns. Based on phylogenetic analyses, morphological characteristics, and minimum, maximum, and optimum temperatures for hyphal growth, the isolate was identified as Phytophthora crassamura. This is the first report of lettuce crown rot caused by P. crassamura in Japan. We propose the name crown rot of lettuce (retasu eki-byo in Japanese) for this lettuce disease.

Since the first report of the tobamovirus tomato brown rugose fruit virus (ToBRFV) in 2014, it has become globally distributed. Its rapid spread has been primarily attributed to seed-borne transmission. Here, the seed-borne nature of ToBRFV transmission was investigated in different cultivars of tomato, bell pepper, and eggplant. In situ hybridization to localize the virus in reproductive organs of ToBRFV-infected tomato plants revealed that the virus was not present in shoot apices, flower buds, or in ovules during flower opening, indicating the virus may be restricted to the outer integument and transported in the vascular bundles during seed development. However, during early fruit development, the virus was present in the integuments in the ovule. Seeds of tomato cultivars with or without tobamovirus resistance gene Tm-2² transmitted the virus to the progeny seedlings at rates that reflected the ineffectiveness of the gene against ToBRFV. Seeds of bell peppers transmitted ToBRFV at higher rates than tomato seeds, but a bell pepper cultivar that has resistance gene L³ was not systemically infected, and its seeds did not harbor the virus. Three eggplant cultivars were systemically infected with ToBRFV but without showing any obvious symptoms, and even though ToBRFV was present in their seeds, the seedlings were not infected. ToBRFV was detected in the seed coats of contaminated tomato and bell pepper seeds, but not in eggplant seed coats. These results indicate mechanistic differences in seed-borne transmission among the three Solanaceae crops.