INFLUENCE OF GROWTH REGULATORS ON THE INFECTION OF ROOTLETS OF APPLE SEEDLINGS IN SARD SOILS BY ACTINOMYCETES

Decapitated apple seedlings which were grown in soils with two levels of specific apple replant disease (SARD) exhibited different levels of rootlet infection by actinomycetes.
When sprayed with several growth regulators or water, NAA and BAP promoted root infection very strongly in both soils.
Gibberellins and water reduced the infection at the lower level of SARD infection.
At the higher level, the application of water and gibberellins gave the same amount of infection as in the control plants.
All three growth regulators enhanced the infection when applied to non-decapitated apple seedlings.
Occurrence of nematodes and colonization of rootlets by VA-mycorrhiza and other fungi were not affected in a similar and consistent way by the growth regulators.
The results confirm the hypothesis that root exudates, as determined by the metabolism of growing terminal buds, contain signal substances which switch on the activities of root-pathogenic actinomycetes and lead to root infection.

III International Symposium on Replant Problems

G. Otto, H. Winkler, K. Szabó

https://doi.org/10.17660/ActaHortic.1994.363.13