Laboratory and field evaluation of cocoa progenies for resistance to mealybug vectors (Hemiptera: Pseudococcidae) of swollen shoot virus.
Resistance of cocoa to Planococcoides njalensis (Laing) was assessed in the laboratory in Ghana by rearing the mealybug from birth until death on 7 cocoa progenies, and determining survivorship, duration of reproduction, gross reproductive rate and live weight. Field evaluation was by sampling both P. njalensis and Planococcus citri (Risso) on the tree trunks and in terminal buds. Progenies 85D/176A × M7/537 and T12/116 × T62/977 were judged the most resistant using the parameters determined in the laboratory. The resistance factor is attributed to antibiosis. The mealybug populations in the field did not show any significant differences among the progenies, but the trend followed the laboratory results. It is suggested that the laboratory method reported here is adequate in assessing resistance, has the advantage of being faster than the field technique and can be used in combination with existing methods for assessing cocoa progenies for resistance to the virus disease.