Molecular markers for the identification and global tracking of whitefly vector– Begomovirus complexes

• Published in: Virus research 2000-11, Vol.71 (1), p.233-260
• Main Author: Brown, J.K.
• Format: Article
• Language: English
• Subjects: Aleyrodidae; Amino Acid Sequence; Animals; Begomovirus; Bemisia tabaci; Capsid - genetics; Emergent viruses; Geminiviridae; Geminiviridae - classification; Geminiviridae - genetics; Geminivirus; Geminiviruses; Genes, Insect; Genes, Viral; Genetic Markers; Genetic Variation; Geography; Hemiptera - genetics; Hemiptera - virology; Insect vector; Insect Vectors - genetics; Invasive species; Molecular epidemiology; Molecular Sequence Data; Open Reading Frames; Phylogeny; Plant Diseases - virology; Sequence Alignment; Species Specificity; Sweetpotato whitefly; Virus Replication - genetics
• ISSN: 0168-1702; 1872-7492
• DOI: 10.1016/S0168-1702(00)00221-5

Recent unprecedented upsurges in populations of the whitefly Bemisia tabaci (Genn.) have drawn much attention to its worldwide importance as an insect pest and as the vector of emergent begomoviruses (Family: Geminiviridae; Genus: Begomovirus). Several begomoviruses that are considered ‘new’ and others previously regarded as minor pathogens have been linked to recent epidemics. Recent studies have revealed much variation in begomoviruses, despite the view that DNA-containing viruses do not rapidly accumulate mutations. Also, certain B. tabaci ‘variants’ are known that more effectively or selectively transmit certain begomoviruses and exhibit biotic differences that may influence their spread. Patterns of distribution and dissemination of begomoviruses transmitted by B. tabaci are poorly understood because standardized molecular-based tracking methods have not been available. Understanding virus/whitefly vector/host plant interrelationships in the context of emerging problems can be achieved only by linking predicted evolutionary histories with epidemiology using molecular phylogenetic approaches. Identification and validation of informative molecular sequences are essential initial steps in this process. Genus-wide degenerate polymerase chain reaction (PCR) primers have been developed to amplify and sequence the ‘core’ region of the coat protein open reading frame (ORF) (V1), permitting ‘universal’ detection and provisional virus identification by comparisons with described viral genotypes. In subsequent studies reported here, several potentially informative viral ORFs and a non-coding region are explored. Of particular use for expanding diversity studies are group- or virus-specific sequences that can be targeted by utilizing newly available core CP sequences, or additional conserved regions around which broad spectrum primers can be designed to target variable sequences in key ORFs or non-coding regions. Prospective markers under exploration were selected with a basis in the most highly conserved viral ORFs, CP (V1) and a portion of replication-associated protein (REP) (L1/C1), and a key non-coding sequence that contain sufficient variability and/or virus-specific sequences, and are consequently of potential epidemiological relevance. Because B. tabaci occurs as a cryptic species, or species complex, that exhibits biotic polymorphism, yet morphological invariance, traditional morphologically based identification is impossible. An overriding complication