Morphological and Molecular Identification of Phytophthora palmivora Causing Heart Rot Disease on Coconut Palm

Abstract

Heart rot disease causing severe decay of spindle leaves and internal crown tissues was observed in coconut plantations cultivated under humid tropical conditions, leading to significant decline and mortality of affected palms. Symptomatic samples collected from infected coconut palms exhibited tissue softening, brown discoloration, foul odor, and progressive rotting of the apical meristem. Diseased tissues were subjected to pathogen isolation and characterization using morphological and molecular techniques to accurately identify the causal organism. Fungal-like isolates consistently produced cottony white colonies with coenocytic hyphae, papillate sporangia, and abundant chlamydospores, characteristic of Phytophthora palmivora. Variability in colony growth and sporulation patterns was observed among isolates obtained from different plantation sites. Pathogenicity tests conducted on healthy coconut seedlings reproduced typical heart rot symptoms, including spindle leaf necrosis and crown tissue decay, confirming the pathogenic nature of the isolates. Re-isolation of the pathogen from inoculated tissues fulfilled Koch’s postulates. Molecular identification was performed through amplification and sequencing of the internal transcribed spacer (ITS) region and other conserved loci commonly used for Phytophthora taxonomy. Sequence comparison revealed high similarity between the obtained isolates and authenticated P. palmivora sequences available in public databases. Phylogenetic analysis clustered the isolates within the P. palmivora lineage with strong bootstrap support, confirming species identity and genetic relatedness among regional isolates. Disease incidence and severity were strongly associated with prolonged rainfall, poor drainage, and high relative humidity, conditions that favored pathogen survival and dissemination. Rapid and reliable identification of P.