Behavior of Phytophthora clandestina propagules at a field site in Western Australia

Abstract

The number of infective propagules of Phytophthora clandestina, an important pathogen of subterranean clover, was estimated by the most probable number (MPN) method in soil at a field site in Western Australia. The behaviour of the propagules of this fungus was studied in relation to root disease index (RDI), disease suppressiveness index (DSI), rainfall, soil moisture and soil temperature for a period of 12 months. There was an increase in the number of infective propagules in the field soil in January and no further increase was observed until May, then marked decrease occurred in June and July with the numbers remaining low through to December. There was no significant correlation between MPN and RDI, DSI, rainfall, soil moisture or temperature. The RDI was, however, negatively correlated (P < 0.05) with DSI linearly (r = 0.76) and quadratically (r = 0.81). Subterranean clover appears to be the sole source of P. clandestina inoculum in the pasture sward of mixed plant species.