Strategy of peach breeding for resistance to diseases in Romania

A breeding programme for peach tree resistance to major diseases began in 1987 at the Research Station for Fruit Tree Growing at Baneasa, Romania. In Romania, significant yield losses in this species are caused by: Taphrina deformans, Sphaerotheca pannosa var. persicae, Cytospora cincta, Monilinia laxa, Pseudomonas syringae pv. syringae, Myzodes persicae and Grapholita molesta. In the recent years, mycoplasma like organisms (MLOs) and virus diseases have been added to the above problem organisms; amongst these Plum-pox induces the most damage. Observations performed on 230 peach and nectarine cultivars and hybrids showed that under the conditions prevailing in Southern Romania, 56% of these were very sensitive to attack by the fungus Taphrina deformans, showing degrees of attack ranging between 50 - 100 %. The hybrids: HE 11 - 46, HE 6 - 39, HB 1 - 8, HB 5 - 11, HB 6 - 23, exhibited resistance to attack by this fungus. The nectarine cultivar Armking was resistant to attack by the fungus Cytospora cincta, while the peach cultivar Clayton was tolerant. Good tolerance of powdery mildew was shown by: Superba de Toamna, Victoria, Triumf, Congres, HE 1 - 3, HE 5 - 3, HE 1 - 8, HE 1 - 1. Particular interest was shown in the crosses: Elberta x Marygold, Flacara x HE 9 - 35, J.H.Hale x Amsden, J.H.Hale x Peen Too, which proved to be uninfected by Plum Pox virus, when tested with ELISA. Following artificial inoculations with Pseudomonas syringae pv. syringae, the peach cultivar Sunglo and the nectarines HCR P8 and HNC demonstrated resistance. The breeding programme for resistance has produced Romanian peach and nectarine cultivars with increased resistance to diseases (Congres, Victoria, Triumf, Flacara, Superba de Toamna). Research performed in recent years has focused on understanding the biochemical mechanisms of resistance, by the identification and role of isoenzymes.