Abnormalities in ‘Starkspur Supreme Delicious’ on Nine Rootstocks in the 1980-81 NC-140 Cooperative Planting

Abstract

‘Starkspur Supreme Delicious’ on MAC.24, OAR 1, M.7 EMLA, M.26 EMLA, O.3, M.9 EMLA, M.9, Mark, and M.27 EMLA were planted at 27 sites in the United States and Canada in 1980-81. During the 10 years of the trial, biotic and abiotic abnormalities occurred. Some were confined to one location while others were more widespread. An outbreak of fire blight ( Erwinia amylovoraBurr) developed in the Virginia trial. Although there was no significant effect of rootstock on the severity of infection initiated in the scion, tree losses varied with rootstock. Tree losses ranged from 67$ and 50% on M.26 EMLA and O.3, respectively, to 0 to 20% for the other rootstocks. In Arkansas, Internal Bark Necrosis occurred; trees on M.27 EMLA and Mark were most severely affected, followed by M.26 EMLA and O.3. The least affected trees were on OAR 1. A growth proliferation occurred on essentially all Mark rootstocks in 7 locations. A swelling was located on the rootstock shank, at the ground line and below, with no apparent relationship to the bud union.