RESULTS OF RESISTANCE TESTS TO ERWINIA AMYLOVORA (BURRILL) WINSLOW ET AL. OF MALUS AND PYRUS PROGENIES WITHIN THE ROOTSTOCK SELECTION PROGRAMME

Within the rootstock selection programme for improving apples and pears, numerous populations from species and cultivated varieties crossings were tested in a greenhouse for their susceptibility to fire blight.
No fire blight resistant Malus or Pyrus clones and progenies were discovered. Malus X micromalus as well as the rootstocks ‘M 4’ and ‘MM 106’ had a medium degree of infestation, whereas ‘M 9’ and ‘M 11’ were highly susceptible.
Among the progenies of ‘M 4’, ‘M 11’ and Malus X micromalus as well as of Pyrus X canescens x P. X serrulata and P. betulifolia x P. ussuriensis, idiotypes with lower susceptibility were discovered, evidently specific combination ability is present.
Less susceptible progenies also can segregate from susceptible parents.
Evidently, an accumulation of resistance genes is necessary for an expression of idiotypic resistance to fire blight.
This indicates a polygenic determination of resistance.
As an indirect method of preventing fire blight, it is important to ensure that newly selected rootstocks are free of suckers.

VII International Workshop on Fire Blight

M. Fischer

https://doi.org/10.17660/ActaHortic.1996.411.81