Resistance of Pear Cultivars in Oregon to Natural Fire Blight Infection

Abstract

In April 1994, severe fire blight infection occurred in a planting of 119 pear cultivar/rootstock combinations. Infection varied from 0 to 59 strikes per tree. Of four replicate trees of each cultivar/rootstock combination, 34, 34, 34, 15, and 2 combinations had infection in 0, 1, 2, 3, and 4 trees, respectively. Jules d'Airolles and Worden Seekel’ on OH x F 333 had fire blight strikes in all trees, with an average of 6.7 and 5.0 strikes per tree, respectively. Over 80% of all fire blight strikes were visible by 9 May. Most of the highly infected cultivars were at full bloom between 16 and 20 April, the time that coincided with extreme risk weather conditions. While some of the noninfected cultivars were well past full bloom when risk was high and may have escaped infection, others were in full bloom and may possess genetic resistance.