Transmission to Apple Seedlings of a Low Molecular Weight RNA Extracted from Apple Scar Skin Diseased Trees

Abstract

Two species of low molecular weight RNA have been associated with apple scar skin disease. One of the RNAs, ASSARNA 1 was detected in the bark tissue as well as in the fruit tissue of diseased apple trees. Inoculation of young seedlings with extracted RNA was performed by rubbing with carborundum or by slashing with a razor. Nucleic acid was extracted from the bark of inoculated seedlings and analysed by two cycles of polyacrylamide gel electrophoresis. ASSARNA 1 was detected in one of 13 seedlings after 28 months following inoculation by the rubbing method with phenol-extracted nucleic acid and in 8 of 14 seedlings after 13 months following inoculation by the razor-slash method with purified ASSARNA 1. The results indicate that ASSARNA 1 was transmitted to apple seedlings and multiplied in them. These facts provided additional evidence for the viroid etiology of the causal agent of apple scar skin disease. However, the pathogenecity of ASSARNA 1 and the role of another disease-associated RNA, ASSARNA 2, are still unknown.