ISHS Acta Horticulturae 489: VIII International Workshop on Fire Blight
THE SUSCEPTIBILITY OF APPLE ROOTSTOCKS AND CULTIVARS TO ERWINIA AMYLOVORA |
| Authors: | James W. Travis, Jo L. Rytter, K. D. Hickey |
| Abstract:
New dwarfing apple rootstocks are continuously being introduced and planted by Pennsylvania growers. These new rootstocks have been observed for various horticultural parameters, however, information on their susceptibility to fire blight and the susceptibility of newer apple cultivars is limited. Results from 1996 field trials in Pennsylvania showed significant differences among seven rootstocks in the percent shoot infection caused by Erwinia amylovora. In order of decreasing to increasing levels of fire blight susceptibility, the pattern observed was G.30, M.7, MARK, B.9, B.491, M.9, and M.26. Two screening techniques were used to evaluate susceptibility. Two concentrations of Erwinia amylovora were used to inoculate plants were inoculated at 3 different leaf positions. Results showed that by inoculating the succulent shoot tip position when compared to two other leaf positions (Travis et al., 1998a), a higher percentage of shoot infection occurred and by using a low concentration of bacterial inoculum, differences among rootstocks were more apparent. In 1997, rootstocks MARK, M.26, M.9, B.9, Ottawa 3, M.7, G.16, and G 30 were inoculated at the shoot tip position using a low concentration of bacterial inoculum. Significant differences were observed among rootstocks throughout the season in the amount of shoot tissue colonized by Erwinia amylovora. In order of decreasing to increasing levels of fire blight susceptibility, the pattern observed was M.7, G.16, MARK, G.30, B.9, M.9, Ottawa 3, and M.26. Results also showed that tree age may be a factor contributing to susceptibility. The long term objectives are to screen rootstocks and rootstock/cultivar combinations for susceptibility to fire blight. On August 25, 1997, the cultivars Rome, York, Fuji, Ginger Gold, Golden Delicious, and Gala were budded onto the rootstocks M.9, B.9, M.7, and Ottawa 3. Trees were inoculated on July 15, 1998. Preliminary results suggest that the number of days for fire blight to move through the cultivar and reach the rootstock is not influenced by the rootstock. | |
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