Evaluation of the resistance of apple, pear and quince varieties to fire blight.
Fire blight has caused economic losses in apples, pears, hawthorn and quince in Qazvin, Iran. The susceptibility of 52 apple and 22 pear cultivars was assessed on scion shoots in the greenhouse by inoculation with 1×109 cells/ml of a mixture of 5 isolates of Erwinia amylovora. A wide continuous spectrum of reaction was observed among the cultivars, which were divided into 4 groups. In apple, the resistant group included the varieties Starking, Improved All Red, Gallobell Blan, Winesap, Red Spar Copper, Meshhad and Red Spar. The progression of bacteria was limited to 1-2 cm, 45 days after inoculation. A similar resistant group was not observed among pear cultivars. Coscia and Khoj were grouped as semi-resistant. In the susceptible group, progression of the bacteria was quick. They penetrated into the 3-year-old wood, droplets of ooze were produced on the branch and it became hooked. Although the symptoms were more severe in the greenhouse, a positive association between natural field reaction and greenhouse symptoms was observed. The local pear variety Darghazi has not shown any disease symptoms in natural epidemics during previous years.