Distribution of Pseudocercospora fruit and leaf spot, Phytophthora foot rot and scab diseases and their effect on Citrus tree decline prevalence in the humid zones of Cameroon

Introduction – Declining Citrus trees (CTD) is a major constraint causing Citrus production depletion in Cameroon. It has been established that some pests and diseases are the major sources of that phenomenon. Improving knowledge of the contributing factors to the occurrence of CTD is key to the control of this. Materials and methods – A study based on the presence of fungal diseases caused by Pseudocercospora angolensis, Elsinoe spp., and Phytophthora spp., was carried out in 39 sites of Citrus producing basins of Cameroon. The aim of the study was to determine environmental factors favouring CTD occurrence in an effort to reducing their devastating effects on three common species of Citrus. Disease symptoms were noticed by examining tree's organs (leaves, fruits, branches, trunk). A regression analysis was applied with the General Linear Model to select the main factors involved in CTD development. The prevalence of CTD was treated as dependent variable. Independent variables were Citrus species, soil texture, vegetation, rainfall, temperature, relative humidity, altitude, observation year, prevalence of PLFSD, Citrus scab and Phytophthora diseases. Results and discussion – CTD was found in all the sites, with a mean prevalence of 25%. Citrus species, soil texture, vegetation, rainfall, Pseudocercospora fruit spot disease, scab, and Phytophthora foot rot disease were the main factors associated with CTD prevalence. Conclusion – The importance of CTD was confirmed. It has been shown that PLFSD and Phytophthora diseases were much more likely to contribute to tree decline contrary to Citrus scab. However, further analysis could pave the way for the development of a risk assessment model for CTD.