Host Resistance in Pyrus to Fabraea Leaf Spot

Pear leaf spot, caused by the fungus Fabraea maculata Atk. (anamorph: Ento- mosporium mespili (DC.) Sacc.) occurs in most areas of the world where pears are grown. Most major cultivars of the european pear, P. communis L., for which data are available are susceptible. Ratings appearing in the literature are sometimes contradictory. This study evaluated resistance/susceptibility within a diverse collection of Pyrus cultivars and other germplasm in a randomized and replicated nursery plot using quantitative measures of disease incidence and severity. The least susceptible genotypes were the P. communis cultivars 'Beurre Fouqueray' and 'Bartlett', the P. pyrifolia cultivars 'Imamura Aki', and the P. communis × P. ussuriensis hybrid NJ 477643275. hybrids. Pure species or interspecific hybrids involving P. calleryana, P. pyrifolia and P. ussuriensis were generally more resistant than P. communis genotypes. Drain (1954) noted resistance in the P. communis × P. pyrifolia hybrids, 'Mooers' and 'Hoskins'. Lombard and Westwood (1987) listed seedlings of P. caucasia and P. cordata Desv. as moderately tolerant, those of the Circum-Mediterranean species P. amygdaliformis, P. elaeagrifolia Pall., and P. syriaca Boiss., and seedlings and clones of P. betulifolia Bunge as having high tolerance, P. calleryana seedlings and clones as very tolerant, and P. pashia D. Don. as susceptible. In contrast to some of the other studies, Lombard and Westwood (1987) list P. pyrifolia and P. ussuriensis as having only low tolerance. One explanation of the disparity among