A rapid in vitro leaf inoculation assay to investigate Phytophthora palmivora–coconut interactions

Abstract

AbstractBud rot, caused by Phytophthora palmivora, is one of the major lethal diseases of the coconut palm. It is a sporadic disease but can assume epidemic proportions occasionally. There is a high risk involved in carrying out studies of plant–pathogen interactions through field trials, especially in a crop like coconut. We have developed an in vitro leaf assay, which would enable an easy and close monitoring of interactions occurring between P. palmivora and coconut during the course of infection by recreating the field infection process in the laboratory. Spindle leaves from adult coconut palms were surface sterilized and inoculated in basal Y3 medium in Petri plates. After a week in culture, the surface of the leaves was pricked and inoculated with zoospore suspension of P. palmivora culture. Typical lesion development was noticed on the surface of the coconut leaves 12–24 hr after inoculation of the pathogen. Electrolyte leakage assays and histological studies using scanning electron microscopy, were also undertaken to study the disease progression. The presence of the pathogen in the coconut leaflets was confirmed using PCR and RT‐PCR with Phytophthora‐specific primers. The pathogen could be re‐isolated from the infected regions, fulfilling Koch's postulates. The novel in vitro leaf assay developed through this study is rapid, space‐effective, precise and inexpensive. It could be utilized for detailed investigations of the qualitative interactions between coconut and P. palmivora.