DYNAMICS OF PACHYMETRA SPORE POPULATIONS: THE EFFECTS OF SITE AND VARIETAL RESISTANCE

THIS IS THE second paper in a series that addresses the dynamics of Pachymetra inoculum in soil, as influenced by initial spore density. This paper compares the results of the first paper with variation in spore dynamics introduced by varietal resistance and field site. Six sites were selected across the northern Queensland district and population increases investigated. There was a clear linear effect of varietal resistance on spore population increase. Resistant varieties limited, but did not totally prevent, spore increases while there very large increases in inoculum density under susceptible varieties. When data from plots of the susceptible Q90 were selected from each site, and initial vs. final spore counts (after plant and first ratoon crop) related, no relationship between initial and final spore counts was found. This means that on occasions, lower spore counts may lead to faster rate of inoculum increase – given a susceptible variety is growing under favourable conditions. Lower increases in Pachymetra inoculum density were found in some plots; this could suggest pathogen suppression. Outcomes from these analyses were compared to previous results on Pachymetra spore dynamics.