Phylogenetic analyses and cross‐infection studies of Phytophthora species infecting cacao and durian in South‐Central Mindanao, Philippines

Phytophthora pathogens have contributed largely to the production losses of plantation crops such as cacao and durian. Correct identification and knowledge of the diversity of the pathogen is a requisite in the formulation of effective management strategies. Fifty‐eight putative Phytophthora isolates were collected from cacao and durian orchards in South‐Central Mindanao, Philippines, with 43 from cacao and 15 from durian. Molecular identification of isolates based on DNA sequences of the internal transcribed spacer (ITS), partial β‐tubulin (β‐tub) and mitochondrial gene (cox2+spacer) regions combined with morphocultural characterization identified 57 Phytophthora palmivora isolates from cacao and durian typically showing variations in colony morphology and sporangial shape. However, these variations were not phylogenetically informative. One Phytophthora meadii (CDDS‐P3) causing pod rot of cacao was phylogenetically isolated from P. palmivora. Phylogenetic analysis of isolates using combined ITS, β‐tubulin (β‐tub) and mitochondrial (cox2+spacer) DNA regions showed an intraspecific variation within P. palmivora. Representative isolates of P. palmivora used for cross‐inoculation showed more aggressiveness on its original host with higher lesion diameter and less aggressiveness on its potential hosts with smaller lesion diameter on artificially inoculated detached plant part. All Phytophthora isolates were tested pathogenic to cacao, durian and its potential hosts (rubber and coconut); therefore, cross‐infection in the field is possible in an intercrop system. Implementation of combined control strategies should be done against highly diverse pathogens such as P. palmivora and the potentially destructive pathogen P. meadii, which was tested pathogenic and virulent to its original (cacao) and potential hosts (coconut, durian and rubber).