ISHS Acta Horticulturae 151: III International Workshop on Fire Blight
COMPARATIVE EVALUATION OF THE DEGREE OF FIRE BLIGHT RESISTANCE IN VARIOUS PEAR CULTIVARS AND SELECTIONS |
| Authors: | T. van der Zwet, R.L. Bell, R.C. Blake |
| Abstract:
As part of the USDA pear breeding program, about 48 major cultivars, 30 pear selections, and 37 world cultivars have been under observation for approximately 20 years for their degree of resistance to fire blight [Erwinia amylovora (Burr.) Winslow et al.] at Beltsville, Maryland and Wooster, Ohio. Of 26 major pear cultivars tested in Maryland, 5 proved to be resistant, 8 moderately resistant, and 13 susceptible. In the Ohio pear collection, 8 cultivars proved to be resistant, 2 moderately resistant, and 12 susceptible. The degree of fire blight in cultivars, and breeding selections grown in both Maryland and Ohio, was generally comparable, but inconsistencies were noted, especially among the most susceptible. Although minimum and lowest yearly average blight scores are in general agreement, the divergence of the two indices of susceptibility varied for different clones and was most pronounced in moderately resistant clones. Use of either score alone can lead to misleading ranking for susceptibility or resistance. In a separate study in Maryland, 2 trees each of about 500 pear cultivars were planted in 1964. By 1971, 38 of the cultivars were rated moderately resistant to resistant to epiphytotic fire blight. Seven of these cultivars are of Oriental origin. To date, all except 1 of the cultivars have maintained resistance to fire blight even though 12 cultivars have shown some degree of blossom, shoot and/or trunk blight following artificial inoculation in the orchard. | |
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