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United States Department of Agriculture

Agricultural Research Service

Title: Differential Susceptibility to Fire Blight in Commercial and Experimental Apple Rootstock Cultivars

Authors
item Fazio, Gennaro
item Aldwinckle, Herb - CORNELL UNIVERSITY
item Mcquinn, R.P. - KEUKA COLLEGE
item Robinson, Terence - CORNELL UNIVERSITY

Research conducted cooperatively with:
item New York State Agricultural Exp. Station, Cornell University

Submitted to: Acta Horticulture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 10, 2004
Publication Date: February 19, 2006
Citation: Fazio, G., Aldwinckle, H., Mcquinn, R., Robinson, T. 2006. Differential susceptibility to fire blight in commercial and experimental apple rootstock cultivars. Acta Horticulture Proceedings (ISHS) 704:527-530.

Interpretive Summary: The Geneva rootstock breeding program has developed several new rootstocks that exhibit resistance to fire blight caused by the bacterium Erwinia amylovora. Utilization of disease resistant apple rootstocks increases the survivability of young trees infected by fire blight. This experiment investigate the possibility that different strains of fire blight may have a rootstock variety specific reaction (i.e. the rootstocks are differentially susceptible to the different strains). We tested a number of commercial and experimental rootstocks for their reaction to four diverse strains of E. amylovora (E2002a, E4001a, E2017, and Ea273). This experiment was conducted on ungrafted potted rootstock liners. These were inoculated with the bacteria by cutting the top two leaves with scissors dipped in the bacterial culture and the resultant necrotic lesions (dead tissue) were measured and used as an indication of susceptibility. The results showed that some strains were more aggressive than others: E. amylovora strain E2002a was the most aggressive, followed by E4001a. E2017a and Ea273 were similar and less aggressive. The six rootstocks with greatest severity of infection in descending order were MM.106, Supporter 4, M.9, M.26, B.118, and B.9. Geneva 3041, 7707, and 5179 and Geneva 16, had least severe infections. We are utilizing this information to breed for durable rootstock resistance to fire blight. In general, rootstocks that show good resistance as ungrafted liners will also show good resistance as grafted finished trees. However, since it is known that a limited number of apple rootstock genotypes react significantly differently to E. amylovora infection as ungrafted potted liners and as rootstocks of flowering orchard trees, the results reported here must be extrapolated to performance in the field with caution.

Technical Abstract: The Geneva rootstock breeding program has developed several new rootstocks that exhibit disease resistance to Erwinia amylovora. Utilization of disease resistant apple rootstocks increases the survivability of young trees infected by fire blight. The goal of this experiment was to further investigate the possibility of differential susceptibility of numerous commercial and experimental apple rootstock varieties to four diversely virulent strains of E. amylovora (E2002a, E4001a, E2017, and Ea273). Ungrafted potted rootstock liners were inoculated with the bacteria and the resultant necrotic lesions were used as an indication of susceptibility. Results showed that the E. amylovora strain E2002a was the most aggressive, followed by E4001a. E2017a and Ea273 were similar and less aggressive. The six rootstocks with greatest severity of infection in descending order were MM.106, Supporter 4, M.9, M.26, B.118, and B.9. In this experiment B.9 had less severe infection than M.9 and M.26, in contrast with a previous experiment by Norelli et al. (2000). Most selections from the Geneva breeding program had little infection by strains E2017 and Ea273 and moderate infection by strains E2002a and E4001a. Most screenings for fire blight resistance in the seedling progenies of the Geneva rootstocks employed only strain Ea273. Geneva 3041, 7707, and 5179 and Geneva16, had least severe infections. Significant rootstock by strain interactions were identified through mixed models analysis. We are utilizing this information to breed for durable rootstock resistance to fire blight. However, since it is known that a limited number of apple rootstock genotypes react significantly differently to E. amylovora infection as ungrafted potted liners and as rootstocks of flowering orchard trees, the results reported here must be extrapolated to performance in the field with caution.

Last Modified: 11/23/2014
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