Resistance to Erwinia amylovora in immature pears induced by acibenzolar-S-methyl in the orchard

Abstract

A field trial was carried out to determine whether resistance to Erwinia amylovora could be induced in unripe pears with acibenzolar-S-methyl (ASM), comparing the effectiveness of ASM with a formulate of copper hydroxide. The random block trial was carried out in a commercial pear orchard between June 15 and 29. The treatments were applied in mid-June. Unripe pears were collected from the trees immediately and 1, 2, 4, 7 and 14 days after treatment, and inoculated in the greenhouse within 2–3 hours with a constant dose of a virulent strain of Erwinia amylovora. After inoculation, the pears were stored in a moist chamber at 25±2°C in a greenhouse, and after 8 days the diameter of each surface lesion was measured as well as its width and depth inside the pulp. In the fruits of ASM treated trees there was a reduction in the lesion diameter of the peripheral tissues around the inoculation holes, but not in the deep pulp tissues. Specifically, the symptoms appeared to be milder in the peripheral tissues even 7 and 14 days after treatment with ASM, especially at the lower concentration. The copper compound gave protection to the immature pears for not more than 4 days. These results justify the use of ASM for the protection of unripe fruit in the spring-early summer period to control bacterial fire blight in pear orchards.