Potentialisation of the biocontrol efficacy of arbuscular mycorrhizas fungi against cocoa black pod rot causing Phytophthora megakarya with natural flavonoid
By: Louise Wakam Nana, Virginie Thérèse Ekounda, Pierre Mkounga, Pierre Eke, Augustin Ephraïm Nkengfack, Dieudonné Nwaga
Key Words: T. cacao, P. megakarya, Arbuscular Mycorrhizal Fungi, Flavonoid, resistance.
Int. J. Agr. Agri. Res. 9(1), 165-181, July 2016.
Cocoa (Theobroma cacao L.) black pod rot, caused by oomycetes Chromista Phytophthora megakarya is the major constraint to cocoa production in Cameroon, causing substantial yield losses (up to 100%). As mean to alter the yield shortage, priority is given to chemical fungicides, though Arbuscular Mycorrhizals Fungi (AMF) have been pointed out to offer a friendly alternative. Moreover, exudation of flavonoids in the mycorrhizosphere could modulate the symbiotic efficiency of these symbionts. Thus, the single and associative effects of two AMF strains (Gigaspora margarita and Glomus intraradices) and a natural flavonoid (3,5,7,3’,4’,5’-hexahydroxy flavanone) were evaluated for their ability to induce tolerance in two cocoa (T. cacao) clones (SNK 10 and ICS 84) against P. megakarya under greenhouse conditions. Also, as biochemical resistance marquers, qualitative (TLC) and quantitative changes in total phenol and flavonoid were assessed Twenty Weeks After Sowing (WAS). The results indicated that, by adding the flavonoid, the AMF significantly improved the growth, total phenol and flavonoid contents as well as the susceptibility of both clones towards P. megakarya. The TLC revealed an enhanced biosynthesis of flavones and anthocyanidins in fresh leaves from the ICS 84 clone which was found to be the least sensitive to P. megakarya. Our results reveal that the dual application of AMF and flavonoid significantly suppresses the black pod disease on cocoa (T. cacao) seedlings, thereby supporting their used to improve the tolerance of cocoa plant against P. megakarya.