Union disorders of almond trees on plum rootstock 1

Almond scions growing on the plum rootstock Marianna 2624 (Prunus cerasifera×P. munsoniana) developed symptoms of deep pits in the xylem and necrotic bark tissues (almond brown line and decline – ABLD) or a mild etching (UME) in the woody cylinder at the union. Trees affected by ABLD decline rapidly while those affected with UME often recover and generally remain in remission thereafter. However, UME-affected trees produce significantly less trunk growth and nut yields. Symptoms of ABLD can be induced by peach yellow leafroll phytoplasma. The etiology of UME is unknown.