Phenolic content and heritability of resistance in four hybrid populations of <i>Theobroma cacao</i> L. after leaves inoculation with <i>Phytophthora megakarya</i> Bras. et Grif

Abstract

Cocoa is cultivated in Cameroon for its broad beans. The commercialization of cocoa seeds constitutes a major source of income to farmers. Nevertheless, cacao black pod disease caused by Phytophthora megakarya is responsible of about 80% of cocoa production loss in Cameroon without any protection method. To assess the resistance of cocoa plants against this pathogen, necrotic lesions and phenolic content were conducted on 3 clones (SNK16, ICS40, Sca12) and their progenies (families F40, F12, F20 and F25) after leaves inoculation. The existence of strong hybrid vigour has been shown. All hybrid genotypes manifested a positive heterosis effect for this symptom suggesting the existence of hybrid vigour. Some hybrids like F40.6, F40.7, F40.8, F40.9, F40.10, F12.10, F12.15, F20.7, F20.10, F25.2, F25.5 and F25.7 were characterized by localized lesions. A negative correlation between the size of necrotic lesions and the total phenolic compound was demonstrated. Three genotypes of the F40 family (F40.8, F40.9 and F40.13), one of the F12 (F12.15) and two of the F25 (F25.2 and F25.8) had small lesions and high concentrations of phenols. These six genotypes can be considered as elite clones with high tolerance to P. megakarya. The values of the heritability of lesion size and the total phenolic content in offsprings don’t show the maternal effect.Keywords: Cocoa, Phytophthora megakarya, heterosis, heritability, necrosis, phenols