Evaluation of the epidemiological aspects of the tomato Golden Mosaic: potentials of possible reservoir and amplifier hosts and spatial dynamics of virus transmission by Bemisia tabaci MEAM1

Abstract

Among the several pathogens that affect the tomato crop (Solanum lycopersicum) the Begomovirus Tomato Severe Rugose Virus (ToSRV) is considered an important infectious agent that affects the production of this crop in Brazil. ToSRV is the causal agent of the golden mosaic of the tomato, transmitted by the Aleirodideo (whitefly) Bemisia tabaci MEAM1 in a persistent-circulatory manner. Despite intense control of the insect in tomato crops through frequent application of insecticides, which prevent the colonization of the vector, the observed incidence of the disease in the field is still high. Despite the important recent progress in understanding the epidemiological dynamics of this pathosystem, some important points still need to be clarified, such as the origin of the inoculum and the spatial dynamics of vector movement and consequent virus transmission. Weed species may act as reservoir for the virus, but because of their low population, they are unlikely to have sufficient strength to act as the main source of the inoculum. This fact suggests that other hosts may perform this task in a more efficient way or the vector may be actively acting in medium and long distance transport of the pathogen that is, introducing the inoculum coming from areas outside the planting limits. Several weed species can house the ToSRV and besides these, cultivated species such as soybean, eggplant, sweet pepper and bean. However, unlike weeds that occur irregularly in the tomato, cultivated plants such as soybean, when susceptible, may exhibit variable rates of asymptomatic infections and are present in large numbers in areas close to tomato crops. Thus, soybean culture could act as an amplifier for the inoculum. As to the vector, some reports in the literature suggest insect movements at medium and long distances, but not, yet, correlated with virus spread, a fact that could help in understanding the dynamics of the disease in the field. From this information, this study aims to evaluate the potential of a reservoir and a possible amplifier host in the incidence of ToSRV in tomato plants and to analyze experimentally the long distance movement of the vector (B. tabaci MEAM1) and the respective ToSRV transmission rates in tomatoes. Also, evaluate the weed infection rates with the ToSRV in the free choice test by B. tabaci MEAM1 and the latency and infectivity periods of the ToSRV in different species susceptible to the virus. The results obtained in this work will provide important information from the epidemiological point of view and could be used in the elaboration of management measures that seek to minimize the impacts caused by this phytovirus in tomato cultivation. (AU)