Peach/myrobalan plum graft incompatibility in the nursery

Various peach/myrobalan graft combinations were compared in nursery trials. Two peach cultivars (Prunus persica L. Batsch) grafted on five myrobalan x myrobalan (Prunus cera- sifera L. Ehrh.) clones were observed during the first year of growth after budding. Graft combinations, comprising the same peach cultivars grafted on other myrobalan x myrobalan clones that had shown symptoms of ‘translocated’ graft incompatibility in some replicated trees during the first year, were observed during the second year of growth. The time taken for the appearance of symptoms of incompatibility was determined. The degree of incompatibility was determined from growth rates, leaf dry weight per unit area, and leaf pigment content. Root carbohydrate content was measured at leaf fall. The sanitary state of plant material was determined to explain differences in severity and/or time for symptom appearance, observed between some replicates. No relationship was found between the sanitary state of plant material and the severity or speed of expression of peach/myrobalan incompatibility. When incompatibility was expressed during the first year of growth, modifications in growth rates, leaf dry weight per unit area and leaf pigment content preceded the expression of visible symptoms on leaves by several weeks. In one peach cultivars, in which graft combinations showed symptoms of ‘translocated’ graft incompatibility in some replicates during the first year after budding, all replicates showed such symptoms during the second year. Therefore, the variation observed during the first year appeared to result from a delayed expression of incompatibility. Significant differences in speed and/or severity of incompatibility expression were shown between the two peach cultivars for any given rootstock.