Variability of in vitro and phenological behaviours of cocoa hybrids based on discriminant analysis

Abstract

Cultivated cocoa species (Theobroma cacao L.) is originated from tropical rainforests of South and Central America. Its fermented and dried seeds constitute the raw material for the chocolate manufacture. In order to analyse the variability of the in vitro and phenological behaviours of 6 cocoa hybrids, the typological and discriminant classifications were performed. These six hybrids developed were : L120-A2, L126-A3, L231-A4, L232-A9, L233-A4 and L330-A9. Three culture media known as PCG1, PCG3 and PCG4, only differing in hormonal concentration, were used as support to sow staminodes and petals from these hybrids. SCA6 and C151-61 were used as controls. After 3 months, callogenesis and embryogenesis variables were scored on each genotype. The Principal Component (PCA), Hierarchical Cluster (HCA) and Factorial Discriminant Analyses (FDA) were used. For the PCA, the number of embryogenic explants, embryos number obtained per embryogenic explant and embryogenesis percentage, as well as flowering level, fructification level and leaves flush were found to be relevant. For the FDA, only the number of callogenic explants and leaves flush were relevant, indicating that the parameters relevance seems to depend on analytical method. Genotypes from cluster C1, namely L120-A2, L126-A3, L231-A4 and L330-A9, expressed the highest callogenesis and leaf flush values. The first 3 were half sibs, with IMC67 as a male common parent. The discriminant function Z1 = -29.123 + 0.201*Flush + 1.71*Ncal discriminated in the proportion of 96.20% the clusters identified. The second discriminant function Z2 did not succeed in discriminating the clusters identified. Indeed, the P from Wilks’ Lambda which is associated with it was not significant. The equation Z1 allows for prediction of the cluster of belonging of a new individual from its callogenesis and leaf flush values. The 4 aforementioned hybrids could be used to produce cocoa aroma, theobromin and cocoa butter from cell suspensions in bioreactors.

Key Words: Callogenesis, Côte d’Ivoire, leaf flush