EVALUATION OF BREEDING RESEARCH ON RESISTANCE TO FUSARIUM OXYSPORUM IN TULIP
The percentage resistance of progenies tested as juvenile (non-flowering) bulblets in the second season was found to be correlated with that recorded for the adult bulbs, indicating that preselection is effective. As both in the juvenile and in the adult phase 'escapes' may occur, a final selection at clonal level is required.
Resistance appeared to be largely based on additive gene action. The most resistant parent cultivars showed generally high General Combining Ability (GCA)-values, i.e. that they transmit a high degree of resistance to their progenies.
Because resistance is primarily based on additive gene action, the extent of resistance of a clone is mostly a reliable indication of the GCA of that genotype. For breeding on resistance, the following procedure proved to be useful: at least one of the parents must have a high degree of resistance. Only progenies which show a high level of resistance during the juvenile phase may be used for further propagation. When from clones selected in these progenies sufficient bulbs are available, a final selection for resistance should be carried out.
Fusarium resistant selections originating from this research have been released to Dutch breeders as 'half-material'. These selections are used in breeding programs, aimed at obtaining resistance of tulip to Fusarium.