Assessment of tolerance level to Phytophthora megakarya in four hybrid populations of Theobroma cacao L.
By: Pierre Effa Onomo, Simon Perrez Akoa, Martine Louise Ondobo, Pierre François Djocgoue
Key Words: T. cacao, P. megakarya, Polyphenols, Enzymes, Heritability.
Int. J. Biosci. 9(3), 53-64, September 2016.
In Cameroon, loss in cocoa seed production is mainly due to Phytophthora megakarya affections. The genetic improvement by controlled hybridisation is one of the methods attempted to minimize black pod disease caused by this fungus. The aim of this study is to generate resistant P. megakarya genotypes through the accumulation of resistant biomarkers. The fungi inoculations were done in the nursery on leaves of four hybrids and three parental clones. Necrosis length, total phenol content, flavonoids, flavan-3-ols, proteins, peroxidase and polyphenols oxidase activities were evaluated on the population under different treatment conditions (healthy, wounded ,wounded and inoculated). Necrosis length was more important in the F70 and F10 families, average in the F30 family and less significant in the F80 family six days after infection. The increasing sensitivity order of the parents based on the progression of the necrosis length is SCA12> T79/467> SNK413. Proteins and bioactive compounds content were genotype-dependent and a strong negative correlations between biochemical metabolites and the necrosis length (P<0.05) were found. Of the four reciprocal crossings realised, two (T79/467 x SCA12 and T79/467 x SNK413) showed a good suitability to the combinations. Also, some hybrids like F80.08, F80.05, F30.05, F30.01 F10.05, F10.06 F70.05 and F70.02 due to their low necrosis and high accumulation of fungicide compounds should be considered as tolerant. The heritability of traits to black pod disease doesn’t show any significant difference suggesting the absence of maternal effect in the transmission of these traits.