Spatial Organisation Influences Citrus <i>Pseudocercospora</i> Leaf and Fruit Spot Disease Severity in Cocoa-Based Agroforestry Systems

Abstract

An investigation to assess the spatial structure and severity of Pseudocercospora leaf and fruit spot disease (PLFSD) on citrus trees in cocoa-based agroforests was carried out in three contrasting ecological zones in southern Cameroon, viz: 1) the humid forest zone, 2) the degraded forest zone, and 3) the forest-savannah transition zone. Two main parameters were investigated viz: 1) the spatial structure of cocoa based agroforests, and 2) the disease severity. In total, the spatial structure of 19 cocoa-based agroforests was analysed using the Ripley K(r) function, meanwhile the collection of epidemiological data that consisted of noting the presence of PLFSD spots on leaves and fruits on 438 citrus trees was used to characterise the severity of the disease. Results showed that, the spatial structure of citrus trees in these agroforests investigated were regular in seven plots, random in nine, and aggregated in three. Aggregated plots presented a significantly higher mean of disease severity on leaves and fruits (28.55 and 30.37 respectively), as compared to randomised (20.91 and 16.32 respectively) and regular plots (16.28 and 14.97 respectively), at P-value < 0.05. These results suggest that the spatial structure of citrus trees in the cocoa-based agroforests studied influences the severity of PFLSD. Proper integrated control measures can therefore be initiated, leading to a considerable reduction of the use of manufactured inputs, and thereby, the cost of production of citrus fruits.

Structural characteristics of cocoa-based agroforestry systems can mitigate citrus Phytophthora foot rot disease intensity

“…Plots with a regular spatial structure were less affected by PFRD and those with an aggregated and random spatial structure were much more affected. Similar results were obtained by (Ndo et al 2019c). (Brown 2004) have suggested that aggregation of host populations enhances pathogen dispersal while regularity decreases it.…”

“…Three main mechanisms illustrate the links between plant composition and the action of pests and diseases via resource variations. These are the mechanism of resource depletion for the pest, resource introduction for the pest, and resource introduction for a natural enemy or vector of the pest (Ngo Bieng et al 2017; Ndo et al 2019c).…”