HYPERSENSITIVITY OF WOODY INDICATORS FOR APPLE STEM GROOVING VIRUS

In grafting experiments apple stem grooving virus could not be detected in Virginia Crab showing stem grooving, brown line and decline. In double-budding experiments with Pyronia veitchii on pear seedling rootstock each of nine single sources of apple stem grooving induced necrosis (brown line) at the union of P. veitchii and its seedling rootstock. In preliminary experiments apple stem grooving virus could not be detected in such affected P. veitchii. In double-budding experiments with the same sources, no symptoms were obtained in P. veitchii on quince A rootstock. The results of the experiments indicate that stem grooving and brown line in Virginia Crab and P. veitchii are hypersensitivity reactions that prevent the virus from becoming systemic in these indicators, and that quince A is immune to apple stem grooving virus. Results of ELISA experiments also indicate that the virus does not invade Virginia Crab systemically.