Effect of AMF-Cacao Association on Pod Disease Incidence in Three-year-old Cacao Trees in an Agroforest in Calauan, Laguna, Philippines

Abstract

Cacao diseases are an important aspect of cacao production that directly translates to losses and yield. Arbuscular mycorrhizal fungi (AMF) are recently studied for their increasing role in disease resistance in many crops, including cacao. In this study, the effects of the different treatments of AMF and biochar applied singly or in combination on the incidence of pod rot diseases – especially the black pod disease – were investigated. Cacao trees were previously treated with AMF and/or biochar during their seedling stage; later, they were assessed for symptomatic pods, three years after field planting. The results showed that there was an interaction (p = 0.043) between treatment and cacao variety on disease incidence. In almost all instances, disease incidence was highest in the control (without AMF) set-up as compared to the amended counterparts. For all varieties, except K2, disease incidence was the lowest on trees with added AMF and biochar amendments. Isolation of fungi associated with symptomatic pods was carried out. However, Phytophthora (the well-known pathogen of black pod disease) was not successfully isolated; hence, the occurrence of black pod disease was unconfirmed. Other fungal genera such as Fusarium, Colletotrichum, Pestalotiopsis, and Lasiodiplodia had the highest occurrence among the fungal isolates. The results from this study support the explored role of AMF associations on disease resistance and plant health on cacao plants in field conditions.