Breeding and Selection of Prunus Rootstocks at the Aula Dei Experimental Station, Zaragoza, Spain

The selection and study of the performance of rootstocks for stone fruit species has been and remains one of the main tasks of the Department of Pomology of the Aula Dei Experimental Station. Initial selection was made from spontaneous Prunus germplasm, mainly open-pollinated, growing in Spain. In the first years, this selection programme included rooting ability as an important trait. Other main objectives were tolerance to calcareous soils and graft compatibility with a wide range of cultivars in the nursery. Elite candidates during these initial screens were virus tested, propagated and tested with a limited number of scion cultivars. Trees were planted in the field and grown under normal management techniques for the area, with records kept for several years, in which growth and fruiting were evaluated. Following this long process, several clonal rootstocks have been released and some of them are already under extensive commercial exploitation: the peach x almond hybrids 'Adafuel' and 'Adarcias', the pollizo plum 'Adesoto', the plum rootstock 'Adara' and the myrobalan 'Ademir'. Currently, the Prunus breeding programme is mainly directed to obtaining new stone fruit rootstocks from hybridisation within Prunus related species and selecting for specific adaptation to unfavourable Mediterranean environments. Good adaptation to replant sites, tolerance to chlorosis and waterlogging, resistance to nematodes and other soil borne pathogens, and graft compatibility are considered priority traits.