Investigating Vector-Virus-Plant interactions influencing transmission efficiency of Tomato yellow leaf curl virus and Tomato mottle virus by Bemisia tabaci

Abstract

The whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) causes crop damage globally by feeding on phloem sap with their piercing-sucking mouthparts, excreting honeydew which promotes growth of sooty mold, and by transmitting viral plant pathogens. Begomoviruses are the largest group within family Geminiviridae and are transmitted by B. tabaci in a persistent and circulative manner. Tomato yellow leaf curl virus (TYLCV) and Tomato mottle virus (ToMoV), are two economically important begomoviruses in the U.S. The overall goals of these studies were to generate new knowledge on vector-virus-plant interactions underlying infection and spread of begomoviruses. The specific objective of the first study presented in Chapter Two is to conduct serial transmission experiments to examine evolutionary relationships of virus-vector and virus-plant interactions responsible for plant infection and whitefly transmission of TYLCV and ToMoV. During each transmission cycle, symptoms were recorded weekly for four weeks, transmission efficiency of whiteflies characterized, virus infections confirmed with PCR, and qPCR was used to quantify titers in the plants. The objective of the experiments in Chapter Three were to further characterize changes in virus titers within individual plants and at different times after inoculation to assess the influence of titer on symptoms and potential for influencing transmission outcomes. Results from experiments in Chapter Two show decreases in viral fitness through time in this closed system, and do not provide significant evidence of adaptation of the virus to the plant or vector after serial transmission. They do, however, provide new information on virus titers of ToMoV, and relationships among virus titers, transmission efficiency, and symptom expression for these two viruses. Findings of Chapter Three provide new information about titers of TYLCV and ToMoV in different leaf positions of the plant, and at four time points after inoculation. Results from these studies are important to better understand virus-vector-plant interactions, and provide guidelines for conducting experimental evolution studies with begomoviruses and B. tabaci.