EFFECTS OF IRRIGATION ON UNINUCLEATE RHIZOCTONIA ON NURSERY SEEDLINGSOF PINUS-SYLVESTRIS AND PICEA-ABIES GROWN IN PEAT GROWTH-MEDIUM

Container seedlings of Scots pine (Pinus sylvestris L.) and Norway spr uce (Picea abies' (L.) Karst) were inoculated with uninucleate Rhizoct onia fungus. The seedlings were grown in a greenhouse in light, low-hu midified sphagnum peat growth medium with three irrigation treatments. The seedlings were irrigated each day, which yelded matric potentials below -2 kPa, or when about -5 or -20 kPa matric potential was achiev ed in the growth medium. It was found that uninucleate Rhizoctonia sp. had a significant effect on mortality, shoot and root dry masses and stem diameter of both pine and spruce seedlings in the daily and -5 kP a irrigation treatments. In the driest -20 kPa treatment, mortality of inoculated seedlings was also high compared with control. The main re sult was that the root dieback caused by uninucleate Rhizoctonia sp. c annot be avoided merely by controlling water supply.