Journal of General Plant Pathology最新文献

In 2023 in Aichi Prefecture, shiso plant growth in a deep flow technique (DFT) hydroponic system was delayed from mid-March to late April with roots showing evidence of rotting. An oomycete species was isolated from the roots and identified as Phytopythium helicoides based on morphological characteristics and DNA sequence homology. Identical symptoms appeared on shiso plants after inoculating seedlings with zoospores from the strain, and the same oomycete species was reisolated from the diseased plants. This study is the first report in the world of root rot caused by P. helicoides in shiso in a DFT hydroponic system.

To prevent threats from pathogens such as Phytophthora species from international plant trade, molecular identification techniques are needed for rapid, accurate quarantine inspection. Here, for quarantine control in Japan, we developed a simple DNA extraction for plants and a practical detection method that combines multiplexed PCR using primers specific for Phytophthora species, for P. nicotianae, which is the only non-quarantine Phytophthora species, and as internal controls, for plants. For the new genus-level primer set, we modified previously reported genus-specific primers to improve detectability. The new primers were able to detect mycelial DNA of 155 taxa among Phytophthora clades 1–10, with a sensitivity of 100 fg/µL for three representative species, P. ramorum, P. kernoviae and P. nicotianae. In the PCRs using DNA from non-target species, amplification was observed for only three taxa, and for some strains, four taxa in a closely related genus. Duplex and triplex PCR of the genus-specific primers combined with previously reported plant primers verified the success of DNA extraction and PCR detection from diseased plant samples, and in the triplex PCR, whether the pathogen was diagnosed as P. nicotianae or not by the species-specific primer. The new method detected the pathogen in naturally infected and inoculated plants. The amplicons using the genus-specific primer have enough variation to be sequenced to identify the species. This new method can be used immediately for detecting Phytophthora species and for quarantine control in Japan.

Soil-borne wheat mosaic virus (SBWMV) in the genus Furovirus is divided into Nebraska-like (NE) group and New York-like (NY) group on genomic sequences. Isolates Hk-Is and Hk-Tk showed more than 97% nucleotide identities to group NE and ca. 90% to group NY both in RNA1 and RNA2, and phylogenetic analyses revealed their affiliation to group NE. Another isolate Kgw, however, was closely and distantly related to the American groups in RNA1 and RNA2, respectively (95% and 88% nucleotide sequence identity to group NE). Consequently, it is concluded that the isolate Kgw is distantly related to the American group.

In early spring of 2020–2022, rot symptoms were observed on onion growing in Iwate and Akita Prefectures. The symptoms exhibited water-soaking rot on leaves, or light brown soft rot on leaf sheaths and bulbs, bringing death of whole plants. From lesions, LOPAT group IVa bacteria were isolated. Based on pathogenicity, bacteriological properties, and sequences of 16S rRNA and housekeeping genes, isolates were identified as Pseudomonas kitaguniensis. This is the first report of bacterial rot of onion caused by P. kitaguniensis. P. kitaguniensis caused strong rot on onion bulbs at 15–25 °C than 30 °C, different from other closely related species.

The tobamovirus, tomato brown rugose fruit virus (ToBRFV), is a significant concern in global tomato production due to the ineffectiveness of the widely used Tm-2² resistance gene. Our previous study showed that the tomato variety GCR237, a Tm-1 homozygote, resisted an Israeli isolate of ToBRFV (DSMZ PV-1241) for up to 35 days post inoculation (dpi), suggesting Tm-1-homozygous cultivars could control ToBRFV. In the present study, we inoculated GCR237 plants with ToBRFV and cultivated them for a longer period of time. The plants resisted systemic infection up to 50 dpi, but mosaic symptoms appeared on the upper leaves by 100 dpi. We retrieved the virus from symptomatic leaves and established four single local lesion isolates. These isolates had several amino acid (AA) substitutions in the helicase domain of 126-kDa/183-kDa replication proteins, where the Tm-1 protein likely binds to inhibit viral RNA replication. Back-inoculating these isolates onto GCR237 plants confirmed they had acquired the ability to overcome GCR237’s resistance and induced mosaic symptoms as early as 14 dpi. About 90% of 229 ToBRFV isolates in the NCBI database had identical AA sequences in the corresponding region to DSMZ PV-1241, while ~ 10% inherently had AA substitutions that would confer complete breaking ability to the Tm-1 resistance. These results suggest that while Tm-1 can inhibit ToBRFV RNA replication, ToBRFV can easily overcome Tm-1 homozygotes.

The species composition of the strawberry anthracnose pathogen population in Saga Prefecture was investigated through phylogenetic analysis of the nucleotide sequences of the intergenic regions of the apn2 and MAT1-2–1 genes. Here, 77 out of the 80 Colletotrichum isolates used were classified as C. fructicola, and the remaining three were classified as C. siamense. The 77 C. fructicola isolates were tested for sensitivity to fludioxonil, which is widely used as the main fungicide in rotational programs in Saga Prefecture. High levels of resistance to fludioxonil were observed in 14 C. fructicola isolates tested for sensitivity to mycelial growth in fludioxonil-containing media. Furthermore, two inoculation assays using strawberry seedlings treated with fludioxonil were performed on five of the 14 isolates that showed high levels of resistance. The effectiveness of fludioxonil was significantly low in these isolates. To our knowledge, this is the first study to report fludioxonil resistance in a C. fructicola population.

Camalexin is the key phytoalexin in Arabidopsis thaliana and crops such as Camelina sativa. It is typically quantified by liquid chromatographic methods using camalexin dilutions as external standards. Alternatively, 6-fluoroindole-3-carboxaldehyde (6-FICA) is used as an internal standard with the advantage that identical conditions can be used for the analyte and standard, but two detectors are needed (ideally fluorescence for camalexin; UV for 6-FICA). We established an easy method to use readily available, cheap thiabendazole as a novel internal standard, facilitating the use of a fluorescence detector for standard and analyte for fast, reliable camalexin quantification in samples of diverse biological origin.

Highly virulent Pseudomonas syringae pv. actinidiae biovar 3 (Psa3) causes kiwifruit bacterial canker, which seriously damages kiwifruits worldwide. We previously screened Psa3-transposon-inserted mutants and obtained reduced-virulence mutants with genes encoding the flagellar protein. Flagella are involved in the motility of bacteria and contribute to P. syringae invasion of plant leaves. However, whether flagella are required for the ability to enter stomata and then multiply in the plant apoplast is not known. Here, we sprayed kiwifruit leaves with Psa3-flagellar-defective mutants and found that their virulence was reduced compared to that of the Psa3 wild type, but their virulence was not reduced when the leaves were infiltrated with Psa3-flagellar-defective mutants using a syringe. Motility and bacterial entry into apoplastic space of the flagellar-defective mutants were also significantly reduced. These results indicate that flagella contribute to Psa3 motility and stomata-mediated entry, leading to disease development, but not multiplication in apoplast space after Psa3 entry. This study provides new insight into bacterial motility in host plants.

In February 2021, damping off and collar and root rot on coriander (Coriandrum sativum L.) became widespread in the municipality of Vitória da Conquista, Bahia, Brazil. An oomycete was isolated from root and collar segments of affected seedlings and caused the same symptoms in inoculated seedlings. Based on morphological features and DNA sequences from the ITS and cox2 region, the pathogen was identified as Pythium aphanidermatum. To the best of our knowledge, this is the first report of the occurrence of P. aphanidermatum on coriander plants in Brazil.

Abstract

Potato spindle tuber viroid (PSTVd; genus Pospiviroid) was detected from pepper (Capsicum annuum) seeds produced in Vietnam during an export inspection. The PSTVd isolate (PSTVd-VN) maintained its viability. The phylogenetic relationship between PSTVd-VN and other PSTVd variants that were isolated from other plants and was classified into lethal and severe strains. PSTVd-VN in tomatoes (cv. Rutgers) caused severe stunting and necrosis of the stems and leaf veins, but no symptoms in inoculated pepper plants except that the fruits were smaller than the control peppers. To our knowledge, this is the first report of PSTVd from pepper seeds produced in Vietnam.