Union aberration of sweet cherry on Prunus mahaleb rootstock associated with X-disease

Several sweet cherry (Prunus avium) scions, including cultivars Bing and Sam, on mahaleb roots (P. mahaleb) developed pits and grooves (aberration) in the wood at the union of the scion and rootstock a year after having been graft-inoculated with tissue from trees with symptoms of X-disease. Graft inoculations of Bing trees on Colt (P. avium × P. pseudocerasus) rootstock produced chronic X-disease symptoms consisting of small leaves and small fruit with short pedicels, but no union aberration