First report of Chayote yellow mosaic virus infecting bitter melon (Momordica charantia) exhibiting yellow mosaic symptoms in Benin, Nigeria, and Togo

Bitter melon (Momordica charantia L.) is widely used as a traditional medicine for the treatment of diabetes in Asia (Fuangchan et al. 2011) and many other diseases in tropical Africa. Yellow mosaic symptoms, frequently associated with family Geminiviridae, genus Begomovirus, were observed in 60 to 80% of M. charantia plants in surveys conducted in three countries in West Africa. In August 2014, leaf samples were collected from three symptomatic and one nonsymptomatic M. charantia plants exhibiting yellow mosaic symptoms in Togo, Benin, and Nigeria (6°10.397′ N; 1°07.316′ E), (6°10.938′ N; 1°09.715′ E), and (7°29′57.5′ N; 3°54′11.3′ E), respectively. Leaves were press dried, and total DNA was extracted as described by Shepherd et al. 2008. The purified DNA from the four samples was separately pooled by country and the viral circular single-stranded DNA was enriched by rolling cycle amplification (RCA) (GE Healthcare Bio-Science, Piscataway, NJ). RCA products (Benin 57 (BN57), Nigeria 35 (NG35), and Togo 54 (TG54) were subjected to Illumina deep sequencing (MisEquation 2 × 150-bp configuration). Sequences were assembled using SeqMan NGen software (DNASTAR, Madison, WI). The assembled, apparently full-length begomoviral genome sequences obtained for all samples were 2,787 bp. BLASTn analysis revealed a closest match of the begomovirus Chayote yellow mosaic virus (ChaYMV) (AJ223191), reported from chayote plants Sechium edule (Jacq.) in Nigeria. Pairwise comparisons carried out using SDT software (Muhire et al. 2013) indicated that the bitter melon isolates (BN57, GenBank Accession No. KT454819; NG35, KT454825; and TG54, KT454820) shared 98 to 100% identity with each other, and 91% with ChaYMV (AJ223191). The genome of the ChaYMV isolates from bitter melon contained six open reading frames (ORFs), CP and V2 in the virion sense strand and Rep, C2, Ren, and C4 on the complimentary sense strand, similar to other previously characterized monopartite begomoviruses, thus suggesting that ChaYMV is a monopartite begomovirus and also because no B-component of a bipartite begomovirus was assembled from the bitter melon samples. No satellites were detected (alpha-and betasatellites). The primer pair ChaF 5′-CGACCCGCAGATATCATCA-3′ and ChaR 5′-ACCGAATCATAGAAATACATCCGTA-3′, designed based on an alignment of the CP gene sequences for the three isolates, was used to PCR-amplify the 758-bp CP gene from each sample, followed by cloning and DNA sequencing. Results indicated they shared 100% nt identity, and were 98 to 100% identical to the NGS assembled sequences. Phylogenetic analyses placed the bitter melon isolates together with AJ223191 (bootstrap value 100%). Based on the ICTV guidelines for species demarcation within the genus Begomovirus, at <91% shared nt identity (Brown et al. 2015), BN57, NG35, and TG54 are distinct bitter melon strains of ChaYMV. Both M. charantia and S. edule together with cucumber, pumpkin, and squash belong to the Cucurbitaceae whose members are commonly infected by begomoviruses worldwide. While S. edule is a widely consumed vegetable crop having high nutritional value, M. charantia is a noncultivated species. The occurrence of ChaYMV in both M. charantia and S. edule suggests that M. charantia is an alternative host of this virus, which is likely transmitted between these species, implicating a role of M. charantia in the epidemiology of ChaYMV for the first time. The identification of ChaYMV in Benin, Nigeria, and Togo strongly indicates that it has a wider-than-reported geographical distribution, and has the potential to become more problematic.