Evaluation of compost quality and bioprotection potential against Fusarium wilt of date palm

The Fusarium wilt of date palm caused by Fusarium oxysporum f.sp. albedinis (Foa) is the most damaging disease in Morocco. It has destroyed more than 12 million trees in the country. Until now, there is no efficient approach to manage this disease. However, biocontrol of soil-borne phytopathogens with compost is currently an established horticultural approach. This study aimed to evaluate the effect of compost extracts in the biocontrol of Foa and their mechanism of action and to investigate parameters involved in compost maturity. Maturity (phytotoxicity test), sanitary quality (pathogen indicators) and in vitro suppressive effect of four composts were investigated. Date palm by-products compost produced with forced aeration composting system is not phytotoxic presenting a germination index of 83.78%. In contrast, two commercial composts were phytotoxic. The maturity was negatively correlated with salinity, C/N ratio and total soluble phenols. Concentrations of pathogen indicators were below suggested limits in all composts. The biocontrol test showed that the date palm wastes compost was more effective; from the sixth day of incubation, the unsterilized extract of this compost at 10% showed the highest antagonistic effect against the pathogen with an inhibition rate of 100%. The inhibition rate using microfiltrated extract didn't exceed 30%. All autoclaved extracts lost their antagonistic effect against the indicator fungus. Thus, the suppressive effect is mainly due to the indigenous microorganisms. Findings indicate the relevance of maturity in the evaluation of compost quality and the efficiency of date palm wastes compost in the suppression of Foa.