Abstract
In order to protect cacao against <i>Phytophthora megakarya</i>, the most aggressive pathogen of this plant in Cameroon, a study was carried out on hybrid genotypes of the family F79SA of cacao (<i>Theobroma cacao</i> L.) to investigate the effect of inoculation of the biofertilizers <i>Gigaspora margarita</i> and <i>Acaulospora tuberculata</i> on the phenolic compound content in hybrid genotypes after leaf infection with <i>Phytophthora megakarya</i> and treatment of salicylic acid (SA). Thus, the phenolic compound content of hybrid genotypes of the family F79SA of <i>T. cacao</i> was evaluated after artificial infection of leaves with <i>P. megakarya</i> and treatment of salicylic acid without control and under control of biofertilizers. The artificial infection of <i>P. megakarya</i> and exogenous application of salicylic acid resulted in an increase in the accumulation of phenolic compounds (PC) in all genotypes. This increase was more important under the control of <i>Gigaspora margarita</i> and <i>Acaulospora tuberculata</i> and varied from one genotype to another. The PC content analysis map of these genotypes at different treatment conditions under the control of biofertilizers showed a gradual evolution of black coloration, a sign of the increase in phenolic compound content related to concentrations of salicylic acid and infected leaves in all hybrid genotypes thus expressing high tolerance. This map allowed to classify hybrid genotypes according to their level of tolerance. A negative and significant correlation (P = 0.05) was observed between the development of necrosis and the accumulation of phenolic compounds on one hand and between salicylic acid and the accumulation of phenolic compounds on the other hand. Salicylic acid can therefore be used in the cacao selection program in the absence of the pathogen for the identification of hybrid cacao genotypes as well as in other similar breeding programs.
Highlights
Cacao (Theobroma cacao L.) is a major annuity crop in Cameroon and in many producing countries that grows in tropical regions with favourable ecological conditions
The phenolic compound content was evaluated in the parental genotypes T79/501, SNK413, and the hybrid genotypes F79SA3, F79SA4, F79SA5, F79SA9, and F79SA21 in the absence of Gigaspora margarita and Acaulospora tuberculata
The genotypes with the highest phenolic content were the most tolerant. This increase was due to the activation of phenylalanine ammonia lyases (PAL), the enzymes most involved in phenolic metabolism, by the elicitors produced by P. megakarya
Summary
Cacao (Theobroma cacao L.) is a major annuity crop in Cameroon and in many producing countries that grows in tropical regions with favourable ecological conditions. Over the last few decades, population growth has led to a considerable demand for cacao as the main ingredient for the chocolate industry. There are several pathogens responsible for fungal diseases, including the pathogenic agent Phythopthora megakarya, responsible for the balck pod disease. This pathogen is recognized as the most aggressive in Central and Western Africa. In Cameroon, it is responsible for losses of up to 80% of the annual yield [6,7]
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