Walter Nkeabeng Leke

Leaves from okra (Abelmoschus esculentus) plants exhibiting unusual viral disease symptoms were tested for the presence of begomovirus infection. The putative full-length Soybean chlorotic blotch virus (SbCBV) components A and B molecules, respectively were amplified, sequenced, and analyzed. This is the first study identifying SbCBV, a bipartite begomovirus infecting okra in Cameroon and the centra Central African region.

Yellow mosaic disease symptoms were observed in 2014 on young papaya (Carica papaya) plants of proximately six to twelve months old, cultivated near Kumba, in the southwestern tropical rainforest o...

Two begomovirus-associated alphasatellites were isolated from okra and a malvastrum plant (Malvaceae) in Cameroon. The complete nucleotide sequences of the okra- and malvastrum-infecting alphasatellites were 1375 and 1416–1418 nucleotides, respectively, and both exhibited features characteristic of other alphasatellites. Based on pairwise sequence comparisons, these previously undescribed alphasatellites are members of distinct species in the genera Colecusatellite and Gosmusatellite and have been tentatively named “pepper yellow vein Mali alphasatellite” and “cotton leaf curl Gezira alphasatellite3”, respectively. Taken together with previous studies, alphasatellites endemic to Cameroon appear to be more diverse and infect plants of many more species and families than currently recognized.

The complete genome sequence was determined and characterized for a previously unreported bipartite begomovirus from fluted pumpkin (Telfairia occidentalis, family Cucurbitaceae) plants displaying mosaic symptoms in Cameroon. The DNA-A and DNA-B components were ~2.7 kb and ~2.6 kb in size, and the arrangement of viral coding regions on the genomic components was like those characteristic of other known bipartite begomoviruses originating in the Old World. While the DNA-A component was more closely related to that of chayote yellow mosaic virus (ChaYMV), at 78 %, the DNA-B component was more closely related to that of soybean chlorotic blotch virus (SbCBV), at 64 %. This newly discovered bipartite Old World virus is herein named telfairia mosaic virus (TelMV).

Here, we report the complete genome sequence of a novel bipartite begomovirus isolated from cotton plants (Gossypium raimondii, Malvaceae) exhibiting light yellow mosaic symptoms. The genome sequence was determined by Illumina DNA sequencing and confirmed by Sanger sequencing of RCA-enriched, cloned circular genomic components. The DNA-A and DNA-B components were each ~2.7 kb in size, and their genome arrangement was characteristic of other Old World bipartite begomoviruses. While the DNA-A component was most closely related to tobacco leaf curl Comoros virus (TbLCKMV) at 80 %, the DNA-B component had as its closet relative soybean chlorotic blotch virus (SbCBV) at 66 %. This previously undescribed begomovirus is herein named “cotton yellow mosaic virus” (CYMV).

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 the family Geminiviridae, genus Begomovirus infection were observed in 60-80% 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 non-symptomatic M. charantia plants exhibiting yellow mosaic symptoms in Togo, Benin, and Nigeria (N: 06o 10.397’ E: 001o07.316’), (N: 06o10.938’, E: 001o09.715’), and (N 07°29’57.5’ E 003°54’11.3’), respectively. Leaves were pressed dried, and total DNA was extracted as described (Shepherd et al. 2008). The purified DNA from the three symptomatic and one non-symptomatic 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, USA). RCA products (Benin 57 (BN57), Nigeria 35 (NG35) and Togo 54 (TG54) were subjected to Illumina deep sequencing (Miseq 2 X150 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 in size. BLASTn analysis using the NCBI GenBank database revealed that the closest match was 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 {GenBank accession number BN57, 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 non-cultivated 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 in time.