Interactions of whitefly bemisia tabaci with a begomovirus and its host plant, solanum lycopersicum
Marchant, Wendy Gay
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Tomato yellow leaf curl virus (TYLCV) is a Begomovirus that causes severe symptoms in tomatoes such as curling of the leaves, chlorosis, stunted growth, and yield losses. The vector is Bemisia tabaci, which transmits the virus in a persistant and circulative manner. TYLCV arrived in Florida in the mid 1990’s and has spread northward into Georgia, South Carolina, and Alabama. TYLCV’s overwintering mechanism is currently unknown, so transovarial and sexual transmission in the whitefly were tested for using PCR and plant transmission experiments, as these modes of transmission could indicate TYLCV overwinters in the whitefly. Transovarial and sexual transmission of TYLCV was found, but the insects were not infectious to plants. TYLCV-resistant tomato cultivars are currently the best method to control for yield losses due to the virus. However, in other pathosystems, viruses have broken resistance in their respective crops. TYLCV genomes isolated from resistant and susceptible cultivars were compared to investigate for this threat. There were not any apparent differences between the genomes, indicating that TYLCV-resistant tomatoes can continue to be of use. Also, many studies have examined the phylogeny and introductions of TYLCV into new geographic regions, but a population genetics approach on a world-wide scale has not been conducted. Hundreds of TYLCV genomes available on GenBank, and from Florida and Georgia, were amassed to test for recombination, polymorphisms, population neutrality, gene flow and genetic differentiation, selection, and phylogeny. The Middle East was confirmed to be the likely origin of TYLCV and showed the highest diversity. In general, the TYLCV species is highly variable and is spreading most rapidly in Southeast Asia. Mixed infections of different Begomovirus species have been reported in many different plants. However, few studies have examined mixed infections of different virus isolates from the same species. Mixed TYLCV infections were sought for in tomatoes from the field. A greenhouse experiment was conducted to assess the competitiveness of two different TYLCV isolates. Lastly, tomato genotypes with acylsugar-exuding trichomes were assessed for whitefly resistance. These genotypes showed xenobiosis and antibiosis toward the whitefly, but were still susceptible to TYLCV inoculation by whiteflies.