ABSTRACT
The foundations of a productive and healthy orchard are the rootstocks that provide anchorage, water and nutrients essential to the above-ground portions of the trees. The utilization of composite trees has increased the efficiency of breeding productive apple trees by dividing the selection of scion traits and rootstock traits into two genetically (and functionally) different specimens, which are then brought together through grafting. The art and science of grafting scions onto rootstocks spans several millennia; it is thought that it was used initially to aid in the clonal propagation of desirable scion varieties for fruit and nut production (Janick, 2005). In these millennia, it is likely that very little attention was dedicated to the selection of a particular rootstock chosen for its properties (ease of propagation) and the properties it imparted to the scion (Tukey, 1964; Rom and Carlson, 1987; Webster, 2003; Webster and Wertheim, 2003). Clonal selection and the beginning of the science of rootstocks seems to have originated in the latter half of the last millennia, where at least for apple, certain rootstock clonal selections were identified to impart unique productivity and architectural properties (early bearing and dwarfing) onto the grafted scion variety (Monceau, 1768). It is very likely that these properties existed or were selected directly on own-rooted trees first as these trees were early bearing, inherently dwarfed and production of fruit from these curious apple plants was early and abundant compared to seedling trees (Loudon, 1822). The combination of small architecture and productivity is adapted to cultivation in fruiting gardens typical of monasteries, aristocratic and wealthy middle-class dwellings (Rivers, 1866). Someone with very practical acuity made the connection that perhaps, by grafting other apple varieties on these early bearing, dwarfed plants the scion would behave in much the same way. Specifically with
the ‘Paradise’ apple, ‘Jaune de Metz’ (Lindley, 1828) otherwise known as Malling 9 (and relatives) the supposition that grafting could make the scion dwarfed was correct and must have led to a revolution of some sort in apple culture because fruit fanciers and nurseries in the eighteenth and nineteenth centuries in central Europe were propagating and using these stocks to make composite dwarfed trees (Hatton, 1917). During this period of discovery there was another important element to these new rootstocks that must have been realized: the seeds from these rootstocks did not breed true, meaning that the early bearing and dwarfing properties were not wholly replicated in all seed progeny. The new rootstocks needed to be propagated clonally to maintain their properties unaltered, hence the possibility of confusion, due to uneven results if a nursery sold trees grafted on seedlings derived from these rootstocks, or had mixtures as their starting material (Hatton, 1920). Major credit needs to be given to the scientists at the East Malling Research Station in the United Kingdom, who in the midst of this confusion collected many clonal rootstocks from around Europe and painstakingly characterized each of them according to their architectural, leafing and flowering properties identified and eliminated duplicates and established what we would call today ‘foundation material’ of rootstocks that were named ‘Malling 1-16’ (Hatton, 1919). Some of these rootstocks (‘Malling 9’ and ‘Malling 7’) became very popular where ‘Malling 9’ (M.9) and its sport mutations became the primary rootstock that fuelled the green revolution of dwarfed apple orchards that occurred in the twentieth century in many apple production regions of the world.
