Yasuhiro Tomitaka's research while affiliated with All-Russian Institute for Plant Protection (VIZR) and other places

The use of Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) for control of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) in the late period of winter–spring greenhouse tomato cultivation was evaluated in a demonstration test in Kumamoto Prefecture, Japan, from 2020 to 2021. Two adjacent greenhouses were used as a control plot and an N. tenuis-introduced plot. Insect-proof nets of 0.3–0.4 mm mesh were used for roof valleys and side walls of the N. tenuis-introduced plot, and 0.8–1.0 mm mesh were used for the control plot. Given the high risk of whitefly invasion in the immediate postplanting period, nonselective insecticides and repellents were used to control whiteflies in both plots initially, then N. tenuis and banker plants were introduced to the N. tenuis-introduced plot. The noncrop plants Cleome hassleriana (Chodat) (Brassicales: Capparaceae) and Verbena × hybrida hort. ex Groenl. & Rumpler (Lamiales: Verbenaceae) were planted as banker plants. N. tenuis introduction tended to suppress the increase in B. tabaci population in spring, the end of the cropping season, and had an indirect positive effect on the suppression of whitefly-transmitted viral diseases to the same or less level than the control. These results indicated that N. tenuis and banker plants, combined with insect-proof net of 0.3–0.4 mm mesh are effective control tools against B. tabaci even in the region which is at high risk for whitefly-transmitted viral diseases.

Squash (Cucurbita maxima) is an essential crop cultivated throughout Japan, and viral diseases such as mosaic disease cause a tremendous loss of squash yield in this region. Although surveying and detection of infectious viruses are essential for controlling viral diseases, currently, no in-depth field surveys have yet been conducted. Here, we conducted a field survey in virus-infected squash fields in Okinawa Prefecture, Japan. A total of 138 samples, including 131 from squash and 7 from weeds, were collected from Ishigaki Island, Miyako Island, and Okinawa Main Island. Nine identified viruses were then investigated by reverse transcription-polymerase chain reaction (RT-PCR). Most samples were found to be infected with zucchini yellow mosaic virus (ZYMV), and a few were infected with papaya ringspot virus (PRSV) or both ZYMV and PRSV. No other cucurbit-infecting viruses were detected among the samples. In addition, ZYMV and PRSV were detected in cucurbitaceous weeds grown near squash fields, suggesting that these weeds may act as an infection source for these viruses. Discipline: Agricultural Environment

In 1929, it was reported that yellowing symptoms caused by a tobacco mosaic virus (TMV) yellow mosaic isolate were suppressed in tobacco plants that were systemically infected with a TMV light green isolate. Similar to vaccination, the phenomenon of cross-protection involves a whole plant being infected with an attenuated virus and involves the same or a closely related virus species. Therefore, attenuated viruses function as biological control agents. In Japan, many studies have been performed on cross-protection. For example, the tomato mosaic virus (ToMV)-L11A strain is an attenuated isolate developed by researchers and shows high control efficiency against wild-type ToMV in commercial tomato crops. Recently, an attenuated isolate of zucchini yellow mosaic virus (ZYMV)-2002 was developed and registered as a biological pesticide to control cucumber mosaic disease. In addition, attenuated isolates of pepper mild mottle virus (PMMoV), cucumber mosaic virus (CMV), tobacco mild green mosaic virus (TMGMV), melon yellow spot virus (MYSV), and watermelon mosaic virus (WMV) have been developed in Japan. These attenuated viruses, sometimes called plant vaccines, can be used not only as single vaccines but also as multiple vaccines. In this review, we provide an overview of studies on attenuated plant viruses developed in Japan. We also discuss the application of the attenuated strains, including the production of vaccinated seedlings.

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.

Tomato brown rugose fruit virus (ToBRFV, a tobamovirus) causes mosaic and severe fruit symptoms on tomatoes and solanaceous crops. Since its discovery in the Middle East a decade ago, ToBRFV has been found in nearly 40 countries. Although it has not yet been reported in Japan, control measures are urgently needed to prepare against ToBRFV. In this study, we tested disinfestation procedures that are already used against tobamoviruses in Japan for their efficacy against ToBRFV: (i) chemical disinfestation of equipment (scissors), (ii) chemicals and dry heat disinfestation of ToBRFV-contaminated tomato seeds, and (iii) inoculation of tomato seedlings with an attenuated strain of tomato mosaic virus (ToMV) to inhibit infection and symptom development. The control measures generally used against tobamoviruses were also effective against ToBRFV on tools and seeds, but the measures differed in efficacy and advantages. The attenuated ToMV was ineffective. Precautions for using these treatments and possible solutions or improvements are discussed.

The tobamovirus tomato brown rugose fruit virus (ToBRFV) causes leaf mosaic and severe fruit symptoms such as browning and distortion (rugosity) on solanaceous crops. Since the first report of ToBRFV in Israel in 2014, it has been found in nearly 40 countries. To obtain further insights on its host range and pathogenicity, detection and preventing its invasion into Japan, we inoculated varieties of solanaceous crops and weeds in a glasshouse with the Israeli ToBRFV isolate and evaluated local and systemic symptoms and infection of the non-inoculated upper leaves. All the tomato varieties tested except for GCR237, homozygous for tobamovirus resistance gene Tm-1, were infected systemically and had mosaic symptoms on leaves. However, rugosity on fruits was very rarely observed on any varieties in our experimental conditions. Bell pepper varieties harboring L¹, L², L³, and L⁴ were resistant or immune to systemic infection. Two Japanese eggplant varieties were systemically infected, but they developed only temporary faint, chlorotic spots and wavy leaves. Most of the other solanaceous crops and weeds tested were also systemically infected by ToBRFV, including newly identified hosts Solanum sisysmbriifolium, S. muricatum, S. ptycunthum, S. nigrescens, and Nicandra physalodes. These results indicate that ToBRFV has a considerably wide host range especially in the Solanaceae.

The family Phenuiviridae comprises viruses with 2–8 segments of negative-sense or ambisense RNA, comprising 8.1–25.1 kb in total. Virions are typically enveloped with spherical or pleomorphic morphology but can also be non-enveloped filaments. Phenuivirids infect animals including livestock and humans, birds, plants or fungi, as well as arthropods that serve as single hosts or act as biological vectors for transmission to animals or plants. Phenuivirids include important pathogens of humans, livestock, seafood and agricultural crops. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Phenuiviridae , which is available at ictv.global/report/phenuiviridae .

In April 2023, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. The phylum was expanded by one new family, 14 new genera, and 140 new species. Two genera and 538 species were renamed. One species was moved, and four were abolished. This article presents the updated taxonomy of Negarnaviricota as now accepted by the ICTV.

We improved an established one-step multiplex RT-PCR method to detect six orthotospoviruses that infect Solanaceae plants (tomato spotted wilt virus [TSWV], newly reported tomato zonate spot virus [TZSV], impatiens necrotic spot virus [INSV], chrysanthemum stem necrosis virus [CSNV], watermelon silver mottle virus [WSMoV], capsicum chlorosis virus [CaCV]). Specific primer sets for one-step multiplex RT-PCR were designed for TSWV, TZSV, INSV, CSNV, WSMoV, and CaCV, and this optimized RT-PCR amplified DNA fragments corresponding to the target virus species: TSWV (831 bp), TZSV (734 bp), INSV (592 bp), CSNV (502 bp), WSMoV (395 bp), CaCV (324 bp). All combinations of orthotospoviruses were detected in mixed samples. The method was applied to Solanaceae plants infected with orthotospoviruses under field conditions.

In 2021 in Kanagawa Prefecture, Japan, green pepper (Capsicum annuum L.) developed necrotic spots on leaves and necrosis of stems. The nucleotide sequence of the N gene of the virus, isolated through two-rounds of single-lesion isolation, shared 95% identity with that of tomato zonate spot virus (TZSV) reported in China. When green pepper plants were inoculated with the isolated virus, the original symptoms were reproduced, and RT-PCR confirmed the presence of the virus in the inoculated plants. This is the first report of TZSV in Japan.