Comparative assessment of detached leaflet and tuber disc assays for studying the aggressiveness of different isolates of Phytophthora infestans

Study of the aggressiveness potentials of a pathogen has wide applications in plant pathology for determination of its population composition and consequent disease control methods in a given environment. Both, laboratory and field experiments are in general use to study the aggressiveness characteristics of plant pathogens. Comparative efficacy and reliability of a particular method employed for such studies could greatly reduce labor hurdles, time and associated costs. In this experiment, we evaluated and compared detached leaflet and tuber disc methods for the reliability of results of the aggressiveness characteristics (percent disease severity, latent infection period and lesion area and area under lesion expansion curve) of 15 isolates of the late blight pathogen (Phytophthora infestans) which were collected from different locations. In general, both methods revealed similar and consistent results for the aggressiveness rankings of different isolates; however, numerical values for aggressiveness components significantly varied among the tested isolates in each method. Results suggested that detached leaflets and tuber discs assay could be used as reliable and efficient methods for studying the aggressiveness characteristics of P. infestans.