PLUM ROOTSTOCKS

The choice of plum scion cultivars depends on local conditions and on available markets for the fruit. But the scion is only half the tree; it is important also to choose a suitable rootstock, to provide the desired size of tree and to suit the soil and climatic conditions.

In the past, incompatibility between scion and rootstock limited the choice, but now vigorous and semi-dwarfing rootstocks are available for all plum cultivars. Plum scions and rootstocks cover a wide range of types and more than one species, but relationship seems to matter very little where compatibility between scion and rootstock is concerned. For instance, the cultivar Czar takes badly on Brussels (both showing characters mainly of Prunus domestica) but grows well on Myrobalan B (P.cerasifera). It is important that the rootstocks should be clonal and true to name, as seedlings and mixed types usually show a wide range of vigour (even after nursery selection) and varying degrees of compatibility. Thus Common Mussel clonal rootstock is compatible with all plum scion cultivars, but a mixture of Mussel types would vary widely, and some could fail to take the bud, or would make trees which would die in the first few years.

Many of the long-established rootstocks have always been propagated vegetatively, but others were traditionally propagated from seed. At East Malling we found clonal material essential to reduce variation in our field trials. Now all recommended plum rootstocks are clonal selections propagated vegetatively. Modern methods enable these to be raised from cuttings as cheaply and as easily as from seed.

Table I lists the plum rootstocks most widely used in England, and Table II shows accumulated crops and tree