FACTORS AFFECTING THE CONTROL OF PYTHIUM-ULTIMUM DAMPING-OFF OF SUGAR-BEET BY PYTHIUM-OLIGANDRUM

Application of Pythium oligandrum to a soil-based compost as a mycelia l suspension (5 x 10(2) CFU g(-1) of dry compost) and oospore alginate pellets (10(5) oospores/g of dry compost) controlled pre- and posteme rgence damping-off of sugar beet caused by Pythium ultimum to a level similar to metalaxyl seed treatment. Oospore seed treatments and aqueo us suspensions of oospores applied to compost failed to control diseas e. Problems in the use of P. oligandrum oospore inocula for the contro l of damping-off were highlighted. It was shown that treatment of oosp ores with cellulase (20 g L-1) increased germination approximately thr ee-fold in comparison to untreated spores. Untreated and cellulase pre treated oospores were subsequently evaluated as seed treatments for th eir ability to control damping-off of sugar beet. The highest rate of pretreated oospores (10(4) oospores/seed) gave levels of emergence and establishment in infested compost that were not significantly differe nt from the uninfested controls, whereas seed treatment with untreated oospores gave no significant reduction in disease. In a trial carried out in a controlled environment to assess the effect of pH (4.5-8.0), P. oligandrum (10(4) cellulase pretreated oospores/seed) was shown to control pre- and postemergence damping-off of sugar beet at pH 7.0 an d 7.5 only.