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Tomato (Solanum lycopersicum) is the most important vegetable and fruit crop in the family Solanaceae worldwide. Numerous pests and pathogens, especially viruses, severely affect tomato production, causing immeasurable market losses. In Taiwan, the cultivation of tomato crops is mainly threatened by insect-borne viruses, among which pepper veinal mottle virus (PVMV) is one of the most prevalent. PVMV is a member of the genus Potyvirus of the family Potyviridae and is non-persistently transmitted by aphids. Its infection significantly reduces tomato fruit yield and quality. So far, no PVMV-resistant tomato lines are available. In this study, we performed nitrite-induced mutagenesis of the PVMV tomato isolate Tn to generate attenuated PVMV mutants. PVMV Tn causes necrotic lesions in Chenopodium quinoa leaves and severe mosaic and wilting in Nicotiana benthamiana plants. After nitrite treatment, three attenuated PVMV mutants, m4-8, m10-1, and m10-11, were selected while inducing milder responses to C. quinoa and N. benthamiana with lower accumulation in tomato plants. In greenhouse tests, the three mutants showed different degrees of cross-protection against wild-type PVMV Tn. m4-8 showed the highest protective efficacy against PVMV Tn in N. benthamiana and tomato plants, 100% and 97.9%, respectively. A whole-genome sequence comparison of PVMV Tn and m4-8 revealed that 20 nucleotide substitutions occurred in the m4-8 genome, resulting in 18 amino acid changes. Our results suggest that m4-8 has excellent potential to protect tomato crops from PVMV. The application of m4-8 in protecting other Solanaceae crops, such as peppers, will be studied in the future. [ABSTRACT FROM AUTHOR]

Papaya ringspot virus (PRSV) causes severe damage to papaya (Carica papaya L.) and is the primary limiting factor for papaya production worldwide. A nitrous acid-induced mild strain, PRSV HA 5-1, derived from Hawaii strain HA, has been applied to control PRSV by cross-protection for decades. However, the problem of strain-specific protection hampers its application in Taiwan and other geographic regions outside Hawaii. Here, sequence comparison of the genomic sequence of HA 5-1 with that of HA revealed 69 nucleotide changes, resulting in 31 aa changes, of which 16 aa are structurally different. The multiple mutations of HA 5-1 are considered to result from nitrous acid induction because 86% of nucleotide changes are transition mutations. The stable HA 5-1 was used as a backbone to generate recombinants carrying individual 3′ fragments of Vietnam severe strain TG5, including NIa, NIb, and CP3′ regions, individually or in combination. Our results indicated that the best heterologous fragment for the recombinant is the region of CP3′, with which symptom attenuation of the recombinant is like that of HA 5-1. This mild recombinant HA51/TG5-CP3′ retained high levels of protection against the homologous HA in papaya plants and significantly increased the protection against the heterologous TG-5. Similarly, HA 5-1 recombinants carrying individual CP3′ fragments from Thailand SMK, Taiwan YK, and Vietnam ST2 severe strains also significantly increase protection against the corresponding heterologous strains in papaya plants. Thus, our recombinant approach for mild strain generation is a fast and effective way to minimize the problem of strain-specific protection. [ABSTRACT FROM AUTHOR]

East Asian Passiflora virus (EAPV) causes passionfruit woodiness disease, a major threat limiting passionfruit production in eastern Asia, including Taiwan and Vietnam. In this study, an infectious cDNA clone of a Taiwanese severe isolate EAPV-TW was tagged with a green fluorescent protein (GFP) reporter to monitor the virus in plants. Nicotiana benthamiana and yellow passionfruit plants inoculated with the construct showed typical symptoms of EAPV-TW. Based on our previous studies on pathogenicity determinants of potyviral HC-Pros, a deletion of six amino acids (d6) alone and its association with a point mutation (F 8 I, simplified as I 8 ) were conducted in the N-terminal region of the HC-Pro gene of EAPV-TW to generate mutants of EAPV-d6 and EAPV-d6I 8 , respectively. The mutant EAPV-d6I 8 caused infection without conspicuous symptoms in N. benthamiana and yellow passionfruit plants, while EAPV-d6 still induced slight leaf mottling. EAPV-d6I 8 was stable after six passages under greenhouse conditions and displayed a zigzag pattern of virus accumulation, typical of a beneficial protective virus. The cross-protection effectiveness of EAPV-d6I 8 was evaluated in both N. benthamiana and yellow passionfruit plants under greenhouse conditions. EAPV-d6I 8 conferred complete cross-protection (100%) against the wild-type EAPV-TW-GFP in both N. benthamiana and yellow passionfruit plants, as verified by no severe symptoms, no fluorescent signals, and PCR-negative status for GFP. Furthermore, EAPV-d6I 8 also provided complete protection against Vietnam's severe strain EAPV-GL1 in yellow passionfruit plants. Our results indicate that the attenuated mutant EAPV-d6I 8 has great potential to control EAPV in Taiwan and Vietnam via cross-protection.