BREEDING OF PEAR ROOTSTOCKS. FIRST EVALUATION OF NEW INTERESPECIFIC ROOTSTOCKS FOR TOLERANCE TO LIME-INDUCED CHLOROSIS AND INDUCED VIGOUR UNDER FIELD CONDITIONS

Seedlings of Pyrus communis or clonal selections of Cydonia oblonga have long been used as pear rootstocks. Although Pyrus communis seedlings are generally used as rootstocks for their tolerance to lime-induced chlorosis, they show an excessive induced vigour for use in intensive orchards. On the other hand, clonal selections of quince rootstocks, such as BA29, ADAMS, SYDO, EMA or EMC, used in most European orchards for their range of reduced vigour, have a restricted utilization in certain growing areas due to their sensitivity to lime-induced chlorosis and/or incompatibility problems with certain cultivars. In 1998, a pear rootstock breeding program, initiated by INRA, was pursued in collaboration between INRA and IRTA to obtain an interspecific rootstock of low vigour, tolerant to lime-induced chlorosis and compatible with the major pear cultivars. Crosses between ‘Pyriam’, a new INRA clonal Pyrus rootstock, and five pear species, Pyrus communis cordata, Pyrus amygdaliformis, Pyrus amygdaliformis persica and Pyrus elaeagrifolia were carried out at INRA. Additionally, seeds from open pollinated “Williams” trees were obtained. Parts of these progenies were planted at IRTA in a highly calcareous soil and were grafted with “Conference”. Over a period of three years, induced vigour and level of chlorosis were evaluated under field conditions. Plants from the crosses with P. elaeagrifolia or P. communis cordata were the least vigorous, and those from crosses with P. elaeagrifolia or P. communis cordata or P. amygdaliformis persica showed a lower degree of chlorosis. The combination of low induced vigour and low chlorosis symptoms indicate than seedlings of ‘Williams’, as well as those obtained from crosses of Pyriam with P. amygdaliformis or P. communis cordata, are interesting and show promise in these conditions.