Factors affecting the control of Pythium ultimum damping-off of sugar beet by Pythium oligandrum.

摘要

Application of P. oligandrum to a soil-based compost as a mycelial suspension (5 X 102 colony forming units/g of dry compost) and oospore alginate pellets (105 oospores/g of dry compost) controlled pre- and postemergence damping-off of sugarbeet caused by P. ultimum to a level similar to metalaxyl seed treatment. Oospore seed treatments and aqueous suspensions of oospores applied to compost failed to control disease. Problems in the use of P. oligandrum oospore inocula for the control of damping-off are highlighted. It was shown that treatment of oospores with cellulase (20 g/litre) increased germination approximately 3-fold in comparison to untreated spores. Untreated and cellulase pretreated oospores were subsequently evaluated as seed treatments for their ability to control damping-off of sugarbeet. The highest rate of pretreated oospores (104 oospores/seed) gave levels of emergence and establishment in infested compost that were not significantly different 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 (104 cellulase pretreated oospores/seed) was shown to control pre- and postemergence damping-off of sugarbeet at pH 7.0 and 7.5 only.