Association of Bemisia tabaci with the Severe Cassava Mosaic Disease in Uganda

Abstract

Severe cassava mosaic disease is associated with East African cassava mosaic virus-Uganda variant (EACMV-UG) in association with African cassava mosaic virus (ACMV). A pseudorecombinant has also been associated with the pandemic. These begomoviruses occur in mixed infections and through synergism the virus titer increases thus resulting in a rich source of inoculum. The interaction of Bemisia tabaci with begomovirus-infected host plants is an important factor implicated in the severe cassava mosaic disease pandemic. Whitefly visual cues to the yellows of infected cassava plants could account for their orientation preference for infected over healthy plants. Based on epidemiological models, such preference with few infected plants could increase the rate of spread of the pathogen and a similar situation could result, if the orientation preference is for healthy plants in the presence of a higher population of infected plants. Disease spread dynamics is exacerbated with high population levels of the vector, which is influenced by an invasive genotype that is particularly fecund, as seen with several other pathosystems around the world and secondly, by plant responses to infection and other stress factors. Plant biochemical reactions to infection result in the availability of nutrients beneficial to the vector. Amino acids for example, have been seen in higher amounts in infected as opposed to healthy plants and with concomitant higher populations of whiteflies on the infected plants. Control measures found to be promising include the use of resistant varieties, use of healthy planting material and roguing. With continued spread of the pandemic these measures represent the epitome of control approaches.