Effects of cacao swollen shoot virus mild strains N1 and SS365B on growth and yield of cacao - a follow-up report
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.
KeywordsTheobroma cacao Cacao Cacao swollen shoot virus Field experiment Growth Long-term Mild strain Yield
The authors wish to thank Kai Johnson (of blessed memory), Henry Oboom, Mawuli Adoblanui, Bright Klu Quarshie, Collins Asomadu, Adolf B. Yiadom and Bernard Armooh (all of CRIG) for providing technical support. The authors are also grateful to Mr. Curt Doetkott, a consulting statistician at the Information Technology Services, North Dakota State University, for analyzing the data, and to Dr. Frank Owusu-Ansah (Biometrician, Social Science and Statistics Unit - CRIG) for support with data management. Funding for this work was provided by CRIG. This manuscript (CRIG/05/2019/040/005) is published with the kind permission of the Executive Director of CRIG.
The experiment was designed, implemented and the manuscript written by OD. GAA and HKD took care of maintenance of the trial at different periods when OD was not at post.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All co-authors have given consent to the publication of this manuscript.
The study did not involve human participants or animals.
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