Heritability of Phenols in the Resistance of Theobroma cacao against Phytophthora megakarya, the Causal Agent of Black Pod Disease

Abstract

The black pod disease caused by Phytophthora megakarya is responsible for 80% of the cocoa production loss in Cameroon. To assess the resistance of cocoa plants against this pathogen, necrotic lesions, phenolic content and qualitative alteration of phenolics were conducted in ICS84 and ICS95 clones (two Trinitario introduced from Trinidad) and their hybrids (families F30 and F25) derived from reciprocal cross breeding between these two parental clones after inoculation. The existence of strong hybrid vigour has been shown. Ninety percentage of the hybrid's genotypes manifested a positive heterosis effect for the development of lesion size. This suggests the existence of hybrid vigour with a genetic additive effect. F3086, F2509, F2552 and F2586 hybrids were characterized by localized lesions. Those hybrids genotypes can be considered as elite clones. In relation to analysis of total phenolics and lesion size, no maternal effect was detected in the transmission of these characters. A significant and negative correlation (r ¼ )0.683) (P < 0.01) has been observed between necrosis evolution and phenolics accumulation. The values of the heritability of lesion size and the total phenolic content in offsprings did not permit to show the maternal effect. Qualitative analyses of phenolics showed high flavonones content in cocoa leaves. Qualitative analyses of phenolics in ICS84, ICS95 clones and their hybrids showed a modification of the phenolics profiles, notably concerning apigenin and luteolin derivatives due to the inoculation. These compounds, along with others that were not identified, could have a role in the reaction and mechanism of defence of cocoa against P. megakarya.

Heterosis, heterobeltiosis, narrow-sense and broad-sense heritabilities for Phytophthora megakarya tolerance in two populations of Theobroma cacao L.

“…Among these flavonoids, flavan-3-ol units are a major class with regards to the reaction of cocoa to stress . This is supported by the findings of Djocgoue et al (2007) who reported that qualitative analysis of phenolics in leaves of cocoa showed a higher accumulation of the flavonoids (luteolin and apigenin derivatives) and some hydroxycinnamic acid derivatives. The significant negative correlation between metabolites (TPP and TF) and length of necrosis trait reflects the importance of the biochemical compounds in tolerance expression.…”

Breeding of parental and tolerant hybrids of Theobroma cacao L. to Phytophthora megakarya Bras. and Griff.

“…However, negative heterosis observed in hybrid genotypes could be explained by the epistatic effect of some genes which tend to mask genes controlling tolerance to P. megakarya. Similar results were also obtained by Djocgoue et al (2007) and Ondobo et al (2014) when leaves of T. cacao were inoculated with P. megakarya. Early studies of Mohammadi et al (2012) showed that, resistance to Septoria tritici blotch is controlled by additive, dominance and epistatic gene action, but the role of the dominant gene effect is greater than the others.…”

Effects of chitosan and snail shell powder on cocoa (Theobroma cacao L.) growth and resistance against black pod disease caused by Phytophthora megakarya

“…These leaf discs were placed with their abaxial surface upwards in side trays. On the other hand, six whole leaves of cocoa were set apart in a single tray and arranged according to the protocol described by Djocgoue et al (2007). These discs and whole leaves were all simultaneously inoculated with 10 µl of 10 6 zoospore ml -1 suspension of P. megakarya.…”

“…The extraction and quantitative measurement of the content of total phenolic compounds were performed as described by Djocgoue et al (2007) with modification. Total phenolic compounds were extracted twice using 80% methanol.…”