Evidences for transmission of Indian cassava mosaic virus through Bemisia tabaci – cassava biotype

Abstract

Indian cassava mosaic virus (ICMV) (Geminiviridae: Begomovirus) is spread primarily through the infected cuttings and secondarily by whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). A cassava adapted haplotype of B. tabaci, referred to as cassava biotype and a polyphagous sweet potato reared population (but does not breed on cassava) identified as sweet potato biotype were reported from India. Recent studies ascertain the cassava biotype of B. tabaci vector ICMV, but sweet potato biotypes do not vector ICMV. This study was initiated to further investigate the ICMV transmission through cassava-biotype population of B. tabaci and its confirmation by serological and polymerase chain reaction (PCR). Virus acquisition access (feeding) period of 48-h on ICMV-infected cassava leaves and 48-h virus inoculation access (feeding) period on virus-free cassava seedling leaves were investigated. ICMV was successfully transmitted from cassava to cassava by cassava biotype. ICMV purified from the experimental cassava plants by sucrose density gradient ultracentrifugation and analysed by immunosorbent electron microscopy (ISEM) using ICMV-specific monoclonal antibodies in which isometric geminate particles of 18 – 20 nm could be detected. A triple-antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) used to detect geminiviruses in the purified cassava, and showed higher viral concentration compared with systemically inoculated tobacco. PCR primers designed from the highly conserved coat protein gene of ICMV – Trivandrum isolate was successfully used for detecting ICMV in stylet, salivary gland and digestive tract of single B. tabaci- cassava biotype after a 48-h acquisition access period, corroborating the role cassava biotype whitefly in the ICMV transmission from cassava to cassava.