Identification of new host plants of swollen shoot virus other than cocoa in Côte d'Ivoire

Swollen shoot disease is one of the most serious threats to cocoa production in Côte d'Ivoire. The pathogen of this disease is a Badnavirus that is transmitted to the plant by vectors that are different species of mealybugs. One of the actions undertaken to fight against this disease is the identification of alternative hosts of CSSV within the crops. In order to identify new host plants of the virus, a trial was set up in the experimental greenhouse of Bouaflé, a swollen shoot endemic area. The plant material consisted of 13 food crops and the positive control (cocoa). The methodology used consisted, on the one hand, in inoculating the CSSTBV viral species under controlled greenhouse conditions with viruliferous mealybugs to 13 food crops (Dioscorea alata, Vigna Subterranea, Phaseolus Vulgaris, Glycine Max, Arachis Hypogaea, Solanum Melongena, Capsicum Annuum, Carica Papaya, Manihot esculenta, Colocasia esculenta, Abelmoschus esculentus, Corchorus olitorius) including the cocoa tree which is the positive control and on the other hand, to trap again mealybugs on food crops two months after inoculation in order to acquire the virus and to repeat them on healthy cocoa trees in order to transmit the virus. After two months of observation of food crops, leaf samples were collected for molecular analysis. Similarly to cocoa, after two months of observation, leaf samples were molecularly diagnosed with the ORF3A primer. The results of the molecular diagnosis revealed the host status of seven (7) new food crops (Corchorus olitorius, Dioscorea alata (florido and bêtê),Vigna subterranea, Phaseolus vulgaris, Arachis hypogaea, Solanum melongena and Manihot esculenta and confirmed the host status of five (5) (Colocasia esculenta, Carica Papaya, Capsicum Annuum and Abelmoschus esculentus). In addition, after retro inoculation, molecular diagnosis revealed that the virus could be transmitted from taro, betê-bêtê yam, florido yam and okra to cocoa, indicating the reservoir and host status of these food crops. These results were confirmed after sequencing of the PCR products. The results obtained will allow on the one hand to enrich the catalog of host and reservoir plants of CSSV and on the other hand, will constitute a decision support tool in terms of food crops not to be associated with cocoa in the perspective of the control of the swollen shoot disease.

Keywords: swollen shoot, food crops, reservoir plants, host plants