A Rootstock is a plant, which already has an established, healthy root system, used for grafting a cutting or budding from another plant. The part being grafted onto the rootstock is usually called the scion. Apple Rootstocks: Apple tree rootstocks are referred to by numbers prefixed by letters indicating the developer of the Rootstock. M : Designates mailing series developed stocks. East mailing research Station in Kent, England collected clones of the Paradise stocks from France in 1912 from which 24 M were designed with no particular order to the Rootstock characteristics other than where assigned. In other words M.2 is larger tree than M.9 while M.27 is smaller than M.26. MM : Designates mailing-Merton stocks developed from joint breeding program by john Innes institute, in Merton, England & East Mailing research Station in the early 1950s. The MM series was developed primarily to provide resistance to Wooly Apple Aphid (Eriosomatinee) Infestation. EMLA...