ISHS Acta Horticulturae 489: VIII International Workshop on Fire Blight
SELECTION FOR FIRE BLIGHT RESISTANCE IN PEAR SEEDLING POPULATIONS USING FIELD AND GREENHOUSE SCREENING WITH VIRULENT STRAINS OF ERWINIA AMYLOVORA. |
| Authors: | D.M. Hunter, W.G. Bonn |
| Abstract:
Pear selections from the Agriculture and Agri-Food Canada pear breeding program (formerly located at Harrow, Ontario) were routinely assessed for reaction to fire blight following introduction of virulent strains of Erwinia amylovora (Burrill) Winslow et al. through inoculation into young actively growing shoot tips on mature trees. Advanced test selections and named introductions from the program had improved levels of resistance as compared with commercial cultivars used as reference standards. Natural fire blight infections were assessed using the USDA scale. All advanced test selections and named cultivars from the program had ratings in excess of 8.5, comparable to or greater than the resistant cultivar ‘Kieffer’, while the susceptible cultivar ‘Bartlett’ was rated below 4. Progeny from controlled hybridizations using resistant selections or introductions from the Harrow program as either seed or pollen parent were screened in the greenhouse by inoculating actively growing shoot tips of young (≈30 cm tall) seedlings with the pathogen. When lesion length as a percent of total shoot length was used to select against those seedlings which had an inadequate level of resistance to fire blight, the deselection (discard) rate in many crosses exceeded 75%. Seedlings with an acceptable level of resistance based on greenhouse screening were planted out in seedling rows. With the transition from a traditional breeding program at Harrow to a biotechnology-based program at Vineland Station, these seedlings were subsequently re-evaluated in the field under a stringent selection regime; only those seedlings showing no or minimal fire blight symptoms were retained for further evaluation. | |
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