Interactions of the Betasatellite component of Begomovirus Complex

Abstract

Whitefly (Bemisia tabaci) transmitted begomoviruses (genus Begomovirus, family Geminiviridae) are economically important phytopathogens infecting dicotyledonous plants. The genomes of begomoviruses consist of either two (components known as DNA A and DNA B) or one (homologous to DNA A) small (2600-2800 nt), circular ssDNA components. Most monopartite begomoviruses are associated with DNA satellites known as alphasatellites and betasatellites.The current study aimed at investigation the interaction of betasatellites with monopartite and bipartite begomoviruses. A quantitative real time PCR (qPCR) assay for the detection of begomovirus/betasatellite/alphasatellite complex associated with cotton leaf curl disease (CLCuD) was developed and used to investigate the relationship between symptoms severity and the virus titre. Not surprisingly, no direct correlation between symptom severity and virus/satellite titre was found. Subsequently, the optimized assay was used to investigate the performance of five selected cotton varieties by using seed cotton yield (SCY) as a measure of plant performance in the 2014 National Coordinated Varietal Trials (NCVT). Virus/satellite DNA levels, symptoms and SCY were found to be highly variable among varieties and their locations. Nevertheless, statistical analysis of the results suggested that betasatellite DNA titres, rather than virus DNA levels, were the important variable in plant performance, having an inverse relationship with SCY. To assess the effects of betasatellites on the bipartite begomovirus Tomato leaf curl New Delhi virus (ToLCNDV), the virus inoculated independently with three betasatellites; CLCuMBMul, CLCuMBBur and TbLCB. Although the results were quite variable, overall the presence of a betasatellite with DNA B enhanced the titres of the DNA B. The studies described here were conducted to obtain a better understanding of interaction between plants and betasatellites and between viruses and betasatellites. A method of determining virus and satellite titre for the components causing CLCuD was developed. Advances made in this regard are discussed.