Browsing by Author "Maboeei, Palesa"
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- ItemSolving the “Colomerus vitis conundrum”: genetic evidence reveals a complex of highly diverged groups with little morphological differentiation(Stellenbosch : Stellenbosch University, 2022-04) Maboeei, Palesa; Van Asch, Barbara; Saccaggi, Davina L.; Wesley-Smith, James; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics. Institute for Plant Biotechnology.ENGLISH ABSTRACT: Colomerus vitis (Acari: Trombidiformes: Eriophyidae) includes bud, leaf curl, and leaf blister eriophyoid mites that cause significant economic damage to grapevines worldwide. It has been hypothesised that different genetic or morphological strains of C. vitis cause the three different plant symptoms. Eriophyoid mites are morphologically simple, and adaptation to different living conditions and hosts generally results in subtle body plan changes which may be difficult to detect using traditional morphological methods. An integrative taxonomic approach including DNA-based (mitochondrial cytochrome oxidase 1 gene variation and Next Generation Sequencing) and morphological analyses (Low temperature Scanning Electron Microscopy imaging) methods was used to investigate the diversity of grapevine eriophyoid mites presumed to be C. vitis. Sanger sequencing of the COI gene in samples of pooled mites collected from grapevine buds and leaf blisters revealed the presence of mixtures of four distinct genetic groups. Subsequent Next Generation Sequencing of the complete mitogenomes of the grapevine mite groups identified by Sanger sequencing was not totally successful but it revealed the presence of a fifth genetic group. The COI sequences had an average intragroup p-distance of 0.82% and an average intergroup p- distance of 20.48%. Based on these results, a multiplex PCR comprising specific primers for each of the five genetic groups was designed to screen samples by capillary electrophoresis with automatic detection of fragment size. Multiplex PCR screenings of bud and leaf blisters consistently confirmed the overall presence of three of the genetic groups in different combinations and proportions. The genetic groups were often found in mixed populations within the same symptomatic grapevine tissue. Bud and blister mites were significantly associated with different genetic groups. The samples used for the analyses were primarily collected in South Africa. Additional samples from the USA, Spain, Israel, and Egypt contributed to insights into the worldwide genetic diversity of C. vitis. Additionally, publicly available C. vitis COI sequences from Iran revealed two other genetic groups, suggesting that the global diversity within C. vitis may exceed what is reported here. For morphological analyses, a total of 67 individual mites collected from grapevines at Nietvoorbij, Western Cape, South Africa from both leaf blisters (n = 45) and buds (n = 22) were analysed using Cryo-SEM imaging. To investigate whether there were any distinct mite morphotypes, specimens were differentiated according to the shape of microtubercles, number of empodial rays, and prodorsal shield patterning. Variations in the morphological characters analysed were observed within the almost indistinguishable species complex. In conclusion, these results indicate that “C. vitis” includes several genetic groups of sufficient diversity to justify the proposal of separate species, rather than strains of a single species each associated with different plant symptoms. These putative species occur in mixed populations within the different plant symptoms, and do not appear to be morphologically unique enough to allow morphological separation of all five species detected here.