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The genetics of resistance to Venturia pirina was investigated from 2002 to 2004 on 11 families derived from interspecific crosses between European and Asian pear species. Nearly complete leaf resistance to V. pirina was identified in all progeny of families with at least 50% Asian pear (Pyrus pyrifolia and/or Pyrus × bretschneideri) ancestry, but up to 26% of these trees exhibited fruit scab incidence in any one of three years. However, between 67% and 80% of the scab leaf resistant individuals had fruit russet spotting owing to scab infection in one or more years over the duration of the trial and between 14% and 36% of the leaves were affected by russet spot. The level of affected individuals did not appear to decrease with increasing proportion of Asian parentage for leaves or fruit. In contrast, reference families derived from European pears and many of the families with 12-25% Asian parentage were almost 100% susceptible to scab on both leaves and fruit. In European families, only 2% of these individuals had leaves affected by russet spotting, whereas an average of 23% of fruit were affected. The genetics of non-host resistance is discussed.

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