Molecular evidence of Cacao swollen shoot virus acquisition and retention by Planococcus citri (Risso) and Pseudococcus longispinus (Targioni-Tozzetti) and Pseudococcus viburni (Signoret) Mealybugs (Hemiptera: Pseudococcidae)

Abstract

Cacao swollen shoot virus (CSSV) remains a significant viral pathogen endemic in West African cacao-growing countries. Eradication of affected trees (complete removal) and resistance breeding in existing cacao (Theobroma cacao L.) germplasm have not yielded the expected results in terms of controlling the spread of CSSV. CSSV is reported to be vectored by at least 16 species of mealybugs (Hemiptera: Pseudococcidae), but there have been no molecular evidences to validate these reports. Inconsistent reports exit on CSSV transmission which were based on visual assessments of CSSV infection which are highly subjective, especially on asymptomatic cacao. The validation of the transmission efficiency of CSSV by mealybugs are arguable. In this study, the presence of CSSV in three mealybug species, Planococcus citri (Risso), Pseudococcus longispinus (Targioni Tozzetti) and Pseudococcus viburni (Signoret), was monitored via PCR after a 72-h virus acquisition access period (AAP) on symptomatic T. cacao (var. Amelonado) seedlings ‘infected’ with New Juaben, a severe strain of CSSV. Solanum tuberosum sprouts were then fed to the mealybugs over a sixday period. Sequenced PCR products of the destructively sampled and CSSV-screened individual mealybug species provided a molecular evidence of CSSV acquisition. qPCR results gave another evidence that CSSV retention is highly variable between and within mealybug species. This is the first molecular evidence highlighting a non-West African mealybug species, Ps. viburni, as a capable CSSV vector. Apparently, these
results could validate the efficacy of non-malvaceous species as barrier crops and in screening for resistance to CSSV vectors in T. cacao.