MM.111 and M.9 apple rootstocks provided drought resistance, but by mechanisms which appear to differ and which may provide benefits to apple trees grown with reduced irrigation or with water stress. The dwarfing rootstock M.9 produces higher levels of ABA that may regulate stomatal opening and improve short-term drought resistance. The more invigorating rootstock MM.111 may be drought hardy in the longer-term due to development of a more extensive root system.