In wild-type Nicotiana benthamiana (WtNb), tobacco mosaic virus (TMV) causes systemic leaf curling, chlorosis/wilting, and eventually necrosis/plant death. Here, we discovered a possible role of the salicylic acid glucosyltransferase gene (SAGT) in lethal TMV–WtNb interactions. SAGT-suppressed Nb (IR) lines had a lower disease index than WtNb and SAGT-overexpressing Nb (OE) lines did. Treatment with benzothiadiazole, which has a suppressive effect on SAGT transcription in WtNb, substantially delayed or abolished systemic necrosis/plant death, but treatment with SA or water did not. Before onset of systemic chlorosis, WtNb and OE lines inoculated with TMV had much higher levels of SAGT transcripts than in IR lines. Among WtNb and all the transgenic lines, IR lines had the highest levels of transcripts for the pathogenesis-related protein 1a gene and the lowest level of TMV. These results suggest that strong induction of SAGT expression may interfere with SA-mediated defensive responses necessary for suppression of lethal symptoms in WtNb infected with TMV.

Since its first occurrence in Israel and Jordan in 2014 and 2015, the tomato brown rugose fruit virus (ToBRFV) has become one of the most concerning pathogens affecting tomatoes and other crops worldwide. Its rapid spread is believed to result from the international trade of contaminated seeds and its seed transmissibility, underscoring the critical importance of seed health testing for ToBRFV to prevent further dissemination of the virus. To this end, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) protocols employing TaqMan probe chemistry have been widely adopted. However, the development of RT-qPCR protocols for ToBRFV seed testing using SYBR Green chemistry remains limited. The SYBR Green method offers the advantage of distinguishing ToBRFV from other tobamoviruses through melt curve analysis. In this study, we developed a SYBR Green-based RT-qPCR detection method using newly designed primer sets, which demonstrated high specificity for ToBRFV and sufficient sensitivity. While this protocol requires further optimization and validation for application in routine seed testing, it establishes a foundational approach for SYBR Green-based RT-qPCR seed testing. Additionally, this study raises an important question regarding the relationship between RT-qPCR results in seed tests and the likelihood of virus contamination or transmission via seeds.

A defective RNA3 (D3Yα) of strain Y of cucumber mosaic virus (CMV-Y) was examined on host-specific maintenance, experimental conditions, and a viral factor required for its generation in plants. D3Yα was stably maintained in cucumber but not in tomato plants for 28 days post inoculation (dpi). D3Yα was generated in Nicotiana tabacum or N. benthamiana after prolonged infection in the second and the third passages, but not in plants of N. benthamiana grown at low temperature at 28 dpi or infected with CMV-Y mutant that had the 2b gene deleted. Collectively, we suggest that generation and retention of D3Yα depends on potential host plants and experimental conditions, and that the 2b protein has a role for facilitation of generation of D3Yα.

Viruses that infect Ranunculus asiaticus L., a globally important greenhouse ornamental, have consistently caused serious damage in Japan. We coupled nextgeneration-sequencing (NGS) with visual assessment of symptoms on leaf tissues, and found almost all of the diseases were caused by ranunculus mild mosaic virus (RanMMV) and ranunculus leaf distortion virus (RanLDV). These results were confirmed by reverse transcription-polymerase chain reaction specific to viral genes of ranunculus-infecting viruses. NGS with symptom assessment should be able to provide a rapid and practical diagnostic method focusing on RanMMV and RanLDV in Japan.

Strawberry powdery mildew caused by Podosphaera aphanis, one of the most important diseases affecting strawberry production in Japan, can be effectively controlled by supplemental ultraviolet (UV) irradiation. Here, we investigated disease severity on plants irradiated with UV light at 270-380 nm with/without inoculation and demonstrated significant decreases in disease severity on the UV-treated plants throughout almost all of the experiment periods. Daily UV irradiation for 3 hr (0.17-0.96 kJ .m(-2) .day(-1)) significantly reduced the incidence of powdery mildew on UV-treated strawberry at day 58 after initiation of UV irradiation in a natural infection and at day 168 in artificial inoculation tests compared with non-UV-treated controls. Furthermore, we found that two pathogenesis-related protein (PR) genes were up-regulated 7 days after initiation of UV irradiation on plants before or after transplantation into raised beds. Transcript levels of five defence-response genes were estimated using quantitative reverse transcription PCR to determine whether UV irradiation induced a defence response; PR-3 and PR-5 transcripts were significantly higher in the UV-treated strawberry leaves after UV irradiation than in the non-irradiated controls. In addition, transcript levels of both genes were significantly up-regulated in plants irradiated with a higher radiant dose (0.90-0.96 kJ .m(-2) .day(-1)) within 7 days after initiation of UV treatment, compared with plants exposed to a lower dose (0.17 kJ .m(-2) .day(-1)) and with controls. Thus, PR-3 and PR-5 are induced in strawberry leaves as part of a defence response that is induced by UV irradiation.