Field evaluation of the protective capability of CSSV mild strain N1 against severe strain New Juaben (1A) isolate
2003
Ollennu, L.A.A., Cocoa Research Institute olGhana, P. 0. Box 8, New Tala, Ghana ., | Owusu, G.K., Cocoa Research Institute of Ghana, P. 0. Box 8, New Tala, Ghana .,
A completely randomised block design trial replicated five times was established at the Cocoa Research Institute of Ghana from 1987 to 2000 to evaluate the protective capability of cocoa swollen shoot badnavirus (CSSV) mild strain Nl. Although 6 300 cocoa plants were inoculated with CSSV mild strain NI on three different occasions, only 2 791 (44.3 %) showed visible symptoms. However, subsequent virobacterial agglutination (VB A) tests on the symptomless plants indicated that 835 (70.0 %) of them contained the mild virus. Forty months after superinoculation with CSSV severe strain 1A, the production of typical symptoms of severe lA was suppressed in I 154 (70.7 %) of the plants which showed visible symptoms of the mild strain. Furthermore, 840 (70.4 %) of the plants which remained symptomless after the repeated N I inoculations also did not produce the severe symptoms of severe IA. This suggests that these plants were infected with the mild strain but remained symptomless. Mild strain NI reduced yield by 446 kg (8.9 %) while the combination of mild strain NI and severe strain IA caused 28.7 per cent (I 443 kg) yield loss within a 4-year period. The yield losses were significant among the treatments. These results suggest that mild strain NI can protect a high proportion of cocoa trees against the devastating effects of CSSV severe IA. The results are discussed with the control of swollen shoot disease in the West African sub-region with particular reference to Ghana.
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