Brown, J. K., & Idris, A. M. (2005). Genetic differentiation of whitefly Bemisia tabaci mitochondrial cytochrome oxidase I, and phylogeographic concordance with the coat protein of the plant virus genus Begomovirus. Annals of the Entomological Society of America, 98(6), 827-837.
Abstract:
Phylogenetic analysis of the Bemisia tabaci (Gennadius) mitochondrial cytochrome oxidase I (mtCOI) sequence grouped populations into one of four major phylogeographic lineages, represented as groups from The Americas-Caribbean Basin (New World) (n = 41), Mediterranean-North Africa-Middle East (n = 47), Asia-Australia (n = 52), and Sub-Saharan Africa (n = 29). The mean genetic variation and percentage nucleotide identities indicated that whitefly populations from the Southeast Asian/ Australian region were the most genetically divergent (1% per lineage/ 106 yr), whereas the Western Hemisphere (Americas-Caribbean region) populations exhibited the lowest degrees of divergence. The phylogenetic tree for the genus Begomovirus (Geminviridae) coat protein (CP) revealed two major phylogeographic lineages with a basis either in the Eastern or Western Hemisphere, respectively. Within the Eastern Hemisphere lineage, the viral CP grouped in one of the three major geographical regions, which were analogous to the mtCOI for the respective geographically associated whitefly populations. Analysis of the CP for the Western Hemisphere viruses revealed two sublineages representative of the 1) North and Central Americas/Caribbean Basin, and 2) South American continent, respectively, which also were phylogeographically concordant with the two major Western Hemisphere B. tabaci mtCOI groups. Analysis of the base substitution rates and synonymous and nonsynonymous changes for the B. tabaci mtCOI coding region suggested that this gene has evolved under positive selection. In total, 26 polymorphic sites (11%) were identified for the species complex, and the fixation of certain amino acids was more evident within certain lineages or populations than others. Collectively, the majority of the 26 polymorphic sites were located at the C-terminal end of the mtCOI fragment that was examined herein. Of the 26 polymorphic sites, only two were net charge-altering amino acids (Y407H and G486K). The genetic differentiation coefficient (GST) for the B. tabaci complex was 59.9%, suggesting that at least moderate genetic differentiation has occurred for the four major extant phylogeographic lineages. This observation is in line with available extant biotic (exclusive vector of begomoviruses; transmission determinants linked to viral CP), morphological (no unique characters), and genetic evidence (single group based on mtCOI, 16SrDNA, and ITS-1 analysis), which supports the hypothesis that B. tabaci comprises a single albeit, cryptic species. Taxonomically, B. tabaci is a species complex, which likely has and continues to experience restricted gene flow in part as the result of geographical and/or host range restrictions. © 2005 Entomological Society of America.
Brown, J. K. (2017). Functional analysis of whitefly B biotype gut gene expression by RNAi knockdown and phenotypic analysis. PLoS One, 12(1), e0168921.doi:10.1371/journal.pone.016892.
Vyas, M., Raza, A., Ali, A.M., Ashraf, M.A., Mansoor, S., Ahmad, A.S., and Brown, J.K. 2017. Knock down of whitefly gut gene expression and mortality by orally delivered gut gene-specific dsRNA. PLoS ONE 12(1): e0168921.doi:10.1371/journal.pone.016892.
Sseruwagi, P., Maruthi, M. N., Colvin, J., Rey, M. E., Brown, J. K., & Legg, J. P. (2006). Colonization of non-cassava plant species by cassava whiteflies (Bemisia tabaci) in Uganda. Entomologia Experimentalis et Applicata, 119(2), 145-153.
Abstract:
Bemisia tabaci (Genn.) (Homoptera: Aleyrodidae) is the vector of cassava mosaic geminiviruses (CMGs), which are the main production constraint to cassava [Manihot esculenta Crantz (Euphorbiaceae)], both in Uganda and elsewhere in Africa. Two B. tabaci genotype clusters, Ug1 and Ug2, differentiated at 8% nucleotide (nt) divergence within the mitochondrial cytochrome oxidase I (mtCOI) gene, have been shown to occur on cassava in Uganda. However, the role of alternative hosts in the ecology of cassava B. tabaci genotypes and their possible involvement in the epidemiology of cassava mosaic disease (CMD) in Uganda remain unknown. In this study, we investigated the restriction of cassava B. tabaci genotypes to cassava and the colonization of alternative host species in select cassava-growing areas of the country in 2003 and 2004. Bemisia tabaci adults and 4th instar nymphs were collected from cassava and 11 other cultivated and uncultivated species occurring adjacent to the sampled cassava fields. Phylogenetic analysis of mtCOI sequences revealed that only a single genotype cluster, Ug1, was present on both cassava and non-cassava plant species sampled in this study. The Ug1 genotypes (n = 49) shared 97-99% nt identity with the previously described cassava-associated B. tabaci populations in southern Africa, and were ∼8% and ∼13% divergent from Ug2 and the 'Ivory Coast cassava' genotypes in Uganda and Ivory Coast, respectively. The Ug1 genotypes occurred (as adults) on all 12 source-plant species sampled. However, based on the presence of B. tabaci 4th instar nymphs, the Ug1 genotypes (n = 13) colonized cassava and five other non-cassava plant species: Manihot glaziovii, Jatropha gossypifolia, Euphorbia heterophylla, Aspilia africana, and Abelmoschus esculentus, suggesting that cassava B. tabaci (Ug1 genotypes) are not restricted to cassava in Uganda. No Ug2-like genotypes were detected on any of the plant species sampled, including cassava, in this study. The identification of additional hosts for at least one genotype cluster, Ug1, known also to colonize cassava, and which was hitherto thought to be 'cassava-restricted' may have important epidemiological significance for the spread of CMGs in Uganda. © 2006 The Netherlands Entomological Society.
Unkefer, C., Molnar, I., Ogden, K. L., Olivares, J., Brown, J. K., & 15 other cauthors, . (2017). Review of the algal biology program within the National Alliance for Advanced Biofuels and Bioproducts. Algal Research, 22, 187-215. doi:10.1016/j.algal.2016.06.002
Legg, J. P., French, R., Rogan, D., Okao-Okuja, G., & Brown, J. K. (2002). A distinct Bemisia tabaci (Gennadius) (Hemiptera: Sternorrhyncha: Aleyrodidae) genotype cluster is associated with the epidemic of severe cassava mosaic virus disease in Uganda. Molecular Ecology, 11(7), 1219-1229.
PMID: 12074729;Abstract:
During the 1990s, an epidemic of cassava mosaic virus disease caused major losses to cassava production in Uganda. Two factors associated with the epidemic were the occurrence of a novel recombinant begomovirus, EACMV-Ug, and unusually high populations of the whitefly vector, Bemisia tabaci. Here we present molecular evidence for the occurrence of two cassava-colonizing B. tabaci genotype clusters, Ug1 and Ug2, one of which, Ug2, can be consistently associated with the CMD epidemic in Uganda at the time of collection in 1997. By contrast, a second genotype cluster, Ug1, only occurred 'at' or 'ahead of' the epidemic 'front', sometimes in mixtures with Ug2. Comparison of mitochondrial cytochrome oxidase I gene sequences for Ug1 and Ug2 and well-studied B. tabaci reference populations indicated that the two Ugandan populations exhibited ≅ 8% divergence, suggesting they represent distinct sub-Saharan African lineages. Neither Ugandan genotype cluster was identified as the widely distributed, polyphagous, and highly fecund B biotype of Old World origin, with which they both diverged by ≅ 8%. Within genotype cluster divergence of Ug1 at 0.61±0.1% was twice that of Ug2 at 0.35±0.1%. Mismatch analysis suggested that Ug2 has undergone a recent population expansion and may be of non-Ugandan origin, whereas Ug1 has diverged more slowly, and is likely to be an indigenous genotype cluster.
