1. Department of Plant Biology; University of Yaounde I; Yaounde Cameroon
2. Department of Mathematics; University of Yaounde I; Yaounde Cameroon
3. CIRAD, UPR Bioagresseurs; Cocoa Research Centre; Trinidad and Tobago
4. Bioagresseurs, University of Montpellier; CIRAD; Montpellier France
5. CIRAD, UMR AMAP; Pretoria South Africa
6. AMAP; University of Montpellier, CIRAD, CNRS, INRA, IRD; Montpellier France
7. Department of Mathematics and Applied Mathematics; University of Pretoria; Pretoria South Africa