Effects of cacao swollen shoot virus mild strains N1 and SS365B on growth and yield of cacao - a follow-up report

Abstract

The cumulative effects of cacao swollen shoot virus (CSSV) mild strains N1 and SS365B on growth and yield of cacao (Theobroma cacao L.) were evaluated in a 12-year field trial at the Cocoa Research Institute of Ghana (CRIG). The treatments consisted of mixed hybrid cacao plants inoculated with N1 or SS365B prior to sowing and a non-inoculated control. Growth of mild strain-inoculated cacao plants did not differ significantly from that of non-inoculated plants. However, growth of N1-inoculated cacao plants was significantly higher than that of SS365B-inoculated ones. The yield of N1-inoculated cacao plants did not differ significantly from that of the non-inoculated plants. However, yield of SS365B-inoculated plants was significantly lower compared to N1-inoculated and the non-inoculated plants. In comparison with the non-inoculated control, yield was 77% and 20% lower in SS365B- and N1-inoculated cacao plants, respectively. Virus indexing conducted over a period of six months on randomly collected budwood from the field revealed the presence of mixed infection of CSSV strains in the field. Cacao tree mortality did not differ among the treatments. These results provide further evidence that the CSSV mild strain N1 is milder in its effect on cacao growth and yield than SS365B and suggest that the former would be a more suitable candidate for cross protection in cacao.