Molecular and experimental evidence of Watermelon (Citrullus lanatus) as host of the Mexican variant of Papaya meleira virus

Papaya sticky disease, caused by Papaya meleira virus (PMeV), results in complete crop loss in papaya orchards, because infected fruits are unacceptable for consumption. Little is known about sticky disease epidemiology, and the best available strategy for disease management is to rogue infected plants. Identification of alternative hosts for this virus is important for developing control strategies. In Mexico, papayas and watermelons are often cultivated in close proximity or overlapping cycles, which may favor virus interspecies transmission by putative insect vectors of PMeV. Watermelon seedlings (Citrullus lanatus Thunb.) were inoculated with latex from papayas infected with a Mexican variant of PMeV (PMeV-Mx), and infection was confirmed by reverse transcription-PCR (RT-PCR) and quantitative RT-PCR (RT-qPCR). Amplicons (491 bp) of the RNA-dependent RNA polymerase (RdRp) gene of PMeV-Mx were detected in axillary leaves of all inoculated seedlings seven days post-inoculation (dpi). Circa 10 to 12 dpi, necrotic lesions were observed on the edges of the leaves. Absolute quantification of PMeV-Mx-RNA by RT-qPCR showed an increase in viral load over time (from 0.51 to 586.15 pg/mu L), three to 14 dpi. Molecular and experimental evidence demonstrate is also a host for PMeV-Mx and may be an alternative host.