Efficacy of thermotherapy combined with chemotherapy and meristem tip culture in reducing Cassava brown streak virus in infected cassava

Abstract

Thermotherapy, chemotherapy and meristem tip culture have been used either alone or in combination to eliminate viruses from plants. . The objective of this study was to determine the efficacy of combining thermotherapy with meristem tip culture and chemotherapy on the reduction of CBSV from infected cassava.Cassava Brown Streak Virus infected cuttings of Guzo variety collected from Coast region of Kenya, were established and maintained in a greenhouse at the Plant Quarantine Station, Kenya Plant Health Inspectorate Service (KEPHIS) in Muguga. Cassava leaves were sampled from eighteen plants and virus indexing done using RT-PCR with virus specific primers. Those confirmed to be positive for CBSV were used as initiation materials for the prospective test plants. From the initiated tissue culture materials, the 2^nd subcultures were subjected to heat treatment at 38°C for 21 days. They were later subjected to ribavirin treatment at varying concentrations of (10mg/l, 20mg/l, and 30mgl) then left to establish for 14 days. Meristems of 1mm were excised from heat treated plantlets at 38°C for 21 days and cultured in vitro in modified Murasgige and skoog media. Nodal plantlets of 10mm not subjected to any treatment were used as controls. There was a significant difference (P<0.01) in the number of plants that survived among the treatments. Thermotherapy combined with chemotherapy resulted in complete mortality of plants due to the high stress levels from the high temperatures combined with the phytotoxic effect of the ribavirin. Thermotherapy followed by excision of meristem tips (1mm) resulted in 68.8% shoot survival with 84% being virus-free. Thermotherapy combined with meristem culture was successfully employed to produce CBSV-free cassava plants.