This chapter discusses the distribution and the economic impact of fire blight (Erwinia amylovora), particularly in North America, Europe, eastern Mediterranean, and the Pacific Rim.

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had been removed by 1990 because of extensive fire blight damage. 'AC Harrow Crisp' out-yielded 'Anjou' and 'Bosc' in the first 5 years of an orchard planted at Summerland, B.C. (Table 1). Shoot. The bark on the sun-exposed side of dormant shoots is brown (RHS 165A, Royal Horticultural Society, 1966). Mean internode length of 'AC Harrow Crisp' was similar to 'Bartlett' and 'Harrow Sweet', but shorter than 'Harvest Queen' and 'Bosc' (Table 2). Leaves. The leaves are elliptic. The shape of the base of the leaf blade is obtuse. The shape of the upper part of the leaf blade is right-angled, with a pointed acuminate tip. There is little curvature of the midrib. Leaf serrations are small and shallow but distinct. The angle between the petiole and the shoot is <30%, the petiole is medium in length, and stipules are absent. The attitude of the leaf in relation to the shoot is upwards. Actively growing shoot tips are reddish-green with light pubescence. Fire blight resistance. As with other introductions from the Harrow pear breeding program (Hunter et al., 1992, 2002; Quamme and Spearman, 1983], 'AC Harrow Crisp' has excellent resistance to fire blight, similar to or greater than that of 'Kieffer', which is used as the standard for selection (Hunter, 1993). Using natural fire blight infection scores (van der Zwet et al., 1970), 'AC Harrow Crisp' had a resistance rating much greater than 'Bartlett' (Table 3). When actively growing shoot tips were inoculated with a mixture of six virulent strains of E. amylovora, the length of the lesion that developed extended to ≈12% of current season's growth, similar to 'Harrow Sweet' and 'Kieffer', but much less than lesion development in 'Bartlett' (Table 3). Bloom and pollination. At Harrow, the time of full bloom of 'AC Harrow Crisp' is

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