ASSOCIATION OF TOMATO RINGSPOT VIRUS WITH APPLE UNION NECROSIS AND DECLINE
Affected trees exhibit symptoms commonly associated with crown or trunk girdling, i.e. sparse, chlorotic foliage; small leaves; short internodal extension; heavy flowering; and large numbers of small, highly colored fruit. Many affected trees crack or break off at the graft union. Removal of the bark in the area of the union reveals abnormally thick, spongy bark and a distinct line at the scion/stock interface. Small, deep pits or o smooth, narrow invagination may penetrate into the union interface. Pegs of brown, necrotic bark tissue frequently are imbedded in the pits or in the invagination. The precise type of union aberration and the presence or absence of necrotic tissue seems to depend upon the particular scion/stock combination.
Succulent terminal leaves from MM106 rootstock sprouts at the base of declining trees were used as a source of inoculum for the mechanical inoculation of a series of herbaceous virus indicator plants. Necrotic, ringspot-type local lesions appeared on Nicotiana tabacum cv. Turkish and several other indicator p1ants within 48–72 hours after inoculation. The virus isolate has been identified as tomato ringspot virus (TmRSV). Subsequently, TmRSV has been isolated from affected MM106 rootstocks from Pennsylvania, Maryland, and New York and from non-budded MM106 rooted layers from Oregon and New York. Tests are in progress to determine the possible etiological relationship between TmRSV and the union necrosis and decline syndrome.