Banana streak badnavirus (BSV) in South Africa : incidence, transmission and the development of an antibody based detection system

Abstract

Various research efforts have focused on Banana streak badnavirus (BSV), the causal agent of banana streak disease (BSD), since the discovery of endogenous sequences of the virus in the nuclear genome of several Musa (banana and plantain) species. In vitro propagation of Musa was identified as one of the main activation triggers of integrated BSV sequences to cause systemic (episomal) BSD. This was especially observed in B genome-containing tetraploid hybrids. Although, the South African banana industry is based on Cavendish varieties, some plantations with tetraploid hybrids have been established. In order to investigate the occurrence of episomally expressed BSV, a survey was done in the Kiepersol area of South Africa and episomal BSV was detected in six out of seven locations sampled. No episomal BSV was detected in the Cavendish cultivars sampled in close proximity to BSV infected cultivars. To determine the risk of vector-assisted spread of endogenous BSV, which has become episomally activated after tissue culture, transmission studies with local mealybug species (Planococcus citri (Risso), P. ficus (Signoret), Dysmicoccus brevipes (Cockerell) and Pseudococcus longispinus (Targioni-Tozzetti)) were conducted under controlled conditions. Virus-free FHIA-21 was multiplied in vitro and resulting progeny with, putatively episomally activated BSV, served as sources for mealybug-assisted transmissions to Cavendish. Activated, episomal BSV was transmitted by three mealybug species to Cavendish. Transmission with P. ficus was demonstrated for the first time. Limited antiserum stocks against BSV occur worldwide and detection of the virus remains crucial for the safe movement of Musa germplasm between continents. Antiserum is needed in order to detect the episomal form of the virus that causes BSD. Using conventional immunization methodology, antisera against a wide spectrum of BSV isolates were produced. Twenty diverse BSV isolates were characterized by IC-PCR and selected as sources for the production of the polyclonal antiserums in two animal species. An effective triple antibody sandwich (TAS) enzyme linked immunosorbent assay (ELISA) system; able to detect various serologically different species of BSV was developed. BSV was screened with a synthetically manufactured phage displayed antibody library; however, no satisfactory polyclonal or monoclonal antibodies were obtianed in using this approach.