Occurrence of a Novel Strain of Moroccan Watermelon Mosaic Virus Infecting Pumpkins in Kenya

Abstract

The potyvirus Moroccan watermelon mosaic virus (MWMV) naturally infects and severely threatens production of cucurbits and papaya. In this study, we identified and characterized MWMV isolated from pumpkin (Cucurbita moschata) intercropped with MWMV-infected papaya plants through next generation and Sanger sequencing approaches. Complete MWMV genome sequences were obtained from two pumpkin samples through NGS and validated using Sanger sequencing. The isolates share 83.4-83.7 % nucleotide (nt) and 92.3-95.1 % amino acid (aa) sequence identities in the coat protein and 79.5-79.9 % nt and 89.2-89.7 % aa identities in the polyprotein with papaya isolates of MWMV. Phylogenetic analysis using complete polyprotein nt sequences revealed the clustering of both pumpkin isolates of MWMV with corresponding sequences of cucurbit isolates of the virus from other parts of Africa and the Mediterranean regions, distinct from a clade formed by papaya isolates. Through sap inoculation, a pumpkin isolate of MWMV was pathogenic on zucchini (Cucurbita pepo), watermelon (Citrullus lanatus), and cucumber (Cucumis sativus), but not on papaya. Conversely, the papaya isolate of MWMV was non-pathogenic on pumpkin, watermelon, and cucumber, but infected zucchini. The results suggest occurrence of two strains of MWMV in Kenya having different biological characteristics associated with the host specificity.