Hot-water Treatment for Sanitizing Forest Nursery Containers: Effects on Container Microflora and Seedling Growth

ISSN： 0282-7581

Source： Scandinavian Journal of Forest Research, Vol.17, Iss.2, 2002-04, pp. : 111-117

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Abstract

Cleaning of containers to counteract infection that might cause root dieback should remove old, adhering media and roots which may harbour pathogens. This study investigated seedling growth and the number of viable fungal propagules retained on the container cavity walls as a result of different container cleaning treatments: washing with cold water (c. 8°C) only, or in addition with a bath temperature of 60, 70, 80 or 95°C for 30 s. More fungal propagules were isolated from containers washed in cold water than from the other treatments. The most frequently isolated fungi were Paecilomyces sp. and Penicillium sp., which are well-known saprophytes. Bacteria and yeast did not seem to be affected by the washing. Electron-microscopic studies of container cavity walls revealed many organic particles and fungal spores on the walls of cold-washed containers. Among other fungal spores there were visible chains of Paecilomyces spp. spores. Containers that were washed at 80°C had some organic debris attached to the cavity walls, but no spores were visible. In used and unwashed containers fungal spores, hyphae and organic debris were found on the container cavity walls. Containers in which the major part of the seedlings previously had suffered from root dieback may have contained a considerable amount of inoculum before washing. Almost 60% of the seedlings grown in unwashed containers had dead or very stunted root systems, whereas about 10% of the seedlings in cold-washed containers suffered from severe root dieback. Additional warm-water treatment further reduced the root dieback of this group of containers. In unwashed containers in which healthy seedlings had been grown, about 4% seedlings and after cold washing no seedlings with root dieback were observed. The cold-washing procedure had a positive effect on seedling height, but there was no additional effect of the warm-water treatment. In conclusion, cold pressurized washing alone does not provide adequate control of root dieback and an additional warm-water bath of at least 60°C is recommended.