Investigations on the cause of soil sickness in fruit trees VII. An actinomycete isolated from rootlets of apple seedlings, the probable cause of specific apple replant disease

Abstract

From earlier investigations it has been deduced, that acti­nomycetes, which colonize and damage the rootlets of apple trees, might be the cause of soil sickness. Attempts to isolate these actinomycetes had been without success for a long time. Foremost, recognizing that plant hormones play a decisive role in the colonization of rootlets by actinomycetes and by introducing such plant hormones into culture media it succeeded to isolate a species of acti­nomycetes, which appeared not earlier. Apple seedlings showed clear diminution of growth in a soil that was steamed and inoculated with this isolate. Additionally, a colonization of rootlets by actinomycetes could be observed, which corresponded in frequency and appea­rance to earlier results from investigations with roots in sick soils. The results are considered a further underpinning of the assumption that root pathogenic actinomycetes are the cause of apple replant disease.