4.7 Article

Spatial and Temporal Analysis of Phytophthora megakarya Epidemic in Newly Established Cacao Plantations

Journal

PLANT DISEASE
Volume 105, Issue 5, Pages 1448-1460

Publisher

AMER PHYTOPATHOLOGICAL SOC
DOI: 10.1094/PDIS-09-19-2024-RE

Keywords

disease development and spread; epidemiology; oomycetes; Phytophthora megakarya; primary infections; spatial pattern; temporal evolution; Theobroma cacao; tropical plants

Categories

Funding

  1. Centre de Cooperation Internationale en Recherche Agronomique pour le Developpement (CIRAD) through ATP Omega3
  2. Centre de Cooperation Internationale en Recherche Agronomique pour le Developpement (CIRAD) through 'Dispositif en partenariat (DP)' Agroforesterie Cameroun
  3. Centre de Cooperation Internationale en Recherche Agronomique pour le Developpement (CIRAD) through ATP Safse

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The study indicates that disease tends to aggregate at short distances, with diseased trees clustering within 3 to 9 meters. Progression of the disease over time is slow, possibly due to rigorous phytosanitation measures and unfavorable microclimatic conditions. Difficulty in pathogen establishment in plots leads to infection dynamics being driven by proximity to already infected cacao plantations.
Studying spatial and temporal plant disease dynamics helps us to understand pathogen dispersal processes and improve disease control recommendations. In this study, three cacao plots devoid of primary inoculum of Phytophthora megakarya (causal agent of cacao black pod rot disease) upon establishment in 2006 were monitored for presence of disease on a weekly basis from 2009 to 2016. Ripley's K(r) function, join count statistics, and Fisher's Exact test were used to analyze spatial and temporal disease dynamics. Disease distribution maps showed aggregated disease patterns in all plots; however, for the years of disease onset, exogenous primary infections were mostly randomly distributed. The K(r) function confirmed these results indicating that inoculum generally disperses only over short distances. Moreover, significant positive spatial autocorrelations showed that diseased trees were often clustered up to a distance of 3 to 9 m. Temporal disease progression was low, meaning that endogenous inoculum failed to establish itself, which is partly explained by rigorous phytosanitation and partly by unfavorable microclimatic conditions for disease development. Because P. megakarya had difficulty establishing itself in the plots, proximity to already infected cacao plantations drove infection dynamics. Thus, isolation of newly established cacao plantations from infected ones and rigorous phytosanitation as a preventive strategy appears to be an effective approach to control cacao black pod rot disease for newly established cacao plantations.

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