Blackheart injury in 'Golden Delicious', 'Jonagold', 'Empire' and 'Rome Beauty' apple trees on five rootstocks in the 1990 NC-140 cultivar/rootstock trial

Blackheart injury was evaluated at 25 cm above the soil surface on 'Golden Delicious', 'Jonagold', 'Empire', and 'Rome Beauty' apple (Malus X domestic a Borkh) trees on M.9 EMLA, B.9, Mark, O.3 and M.26 EMLA rootstocks in the 1990 NC-140 cultivar by rootstock plantings located in Indiana, Iowa, Kentu cky, Maine, Massachusetts, Ohio, and Tennessee. Trees grown in Iowa, which recorded the coldest temperatures, exhibited the greatest injury, while tre es grown in Tennessee, Massachusetts, and Maine exhibited the least injury. Cultivar susceptibility to blackheart injury was affected by location, wit h Jonagold trees sustaining a high percentage of injury in Iowa and Indiana , and Rome trees sustaining high injury in Indiana, Kentucky, Maine, and Ma ssachusetts. Trees on Mark rootstock, followed by B.9 and M.9 EMLA, most fr equently exhibited a high percentage of blackheart injury, while trees on M .26 EMLA, followed by O.3, most frequently sustained less blackheart injury . Supplemental decline ratings of trees in the Iowa planting in conjunction with the blackheart injury support reports that trees on Mark and Low temp erature tolerance of apple trees on dwarfing rootstocks is a concern in col der apple-producing regions. Trees have been killed following test winters, but more often exhibit symptoms of decline from which recovery often occur s. Injury can be to the roots or the above-ground portions of the trees. Ro ot injury typically occurs under conditions where trees are growing on sand y soils and absence of snow cover during a freezing event (16). Depending u pon when the freezing event occurs,injury to the above-ground portions of t he trees can be to the xylem, bark, or buds. mid-winter, apple vegetative b uds and bark are much hardier than living xylem cells, while xylem is hardi er than the bark and buds in early autumn and late spring (17, 18). Blackhe art is a form of winter injury characterized by the killing ok xylem parenc hyma cells and the occlusion of vessel elements (22). The typical symptom o f blackheart is oxidative browning of the xylem tissue (20) caused by the s upercooled fraction of intercellular water freezing in the xylem ray parenc hyma cells (17, 18). Most often, blackheart injury does not cause outright death of the plants with recurring injury being common in nature, and it ha s been implicated in the decline and reduced productivity of fruit trees (1 7).