Characterization and detection of Passiflora mottle virus and other two potyviruses causing passionfruit woodiness disease in Vietnam.

Passionfruit plantation in Vietnam increased to 10,000 ha in 2019. However, the outbreaks of passionfruit woodiness disease (PWD) have become a serious threat for the production. In this study, five virus isolates DN1, DN4, NA1, GL1 and GL2 were collected from different areas of Vietnam. Their causal roles for PWD were verified by back inoculation to passionfruit. Analyses of coat protein (CP) and genomic sequences revealed that GL1 isolate is closely related to East Asia Passiflora virus (EAPV) AO strain of Japan (polyprotein nt/aa identities of 98.1% / 98.2%), while GL2 isolate is related to Telosma mosaic virus (TelMV) isolate PasFru, China (polyprotein nt/aa identities of 87.1% / 90.9%). CP comparison, host range and cytological characterization indicated that DN1, DN4 and NA1 are potyviruses, but different from EAPV and TelMV. Phylogenic analyses of their CP and genome sequences indicated that these three isolates and passionfruit severe mottle-associated virus Fujian isolate of China belong to a distinct clade, which does not satisfy the threshold (76% nt identity of polyprotein) to be regarded as any of potyviral species. Thus, a new species name of "Passiflora mottle virus" has been proposed by ICTV. A rabbit antiserum was produced against the CP of DN1 and it can discriminate Passiflora mottle virus (PaMoV) from TelMV and EAPV in western blotting and ELISA without cross reactions. Field surveys of 240 samples by ELISA and RT-PCR disclosed that PWD in Vietnam is mainly caused by PaMoV; followed by EAPV, mixed-infection of PaMoV/EAPV, and rare cases of TelMV.