Articles
APPLE DECLINE
The symptoms of decline are small rolled leaves, lack of terminal growth, and limb dieback.
The disorder appears to spread concentrically from one point in the orchard.
Root systems of these trees generally look normal, except for an obvious absence of small feeder roots.
A 100% correlation with DAPI-positive(4′-6-diamidino-2-phenylindole) organisms and Apple Decline was observed in roots of diseased trees.
Oxytetracycline was injected into declining apple trees in the fall.
The following spring, the oxytetracycline-injected trees exhibited increased feeder root growth and improved shoot growth.
The incidence of DAPI-positive organisms declined significantly after oxytetracycline injections.
Four years after injection, the trees still appear more vigorous than the untreated controls.
These results suggest a mycoplasma-like organism (MLO) is the causal agent of Apple Decline.
Total DNA was extracted from either apple decline-infected or normal appearing apple tree roots using the procedure described by Dellaporta et al (1983). A MLO-enriched DNA fraction was prepared and cloned.
Presently, the clones are being screened as possible diagnostic probes.