Induction of resistance in Yali pear (Pyrus bretschneideri Rehd.) fruit against postharvest diseases by acibenzolar-S-methyl sprays on trees during fruit growth

The objective of this work was to evaluate how disease resistance in harvested fruit of Yali pears (Pyrus bretschneideri Rehd.) may be affected by acibenzolar-S-methyl (ASM) sprays on trees. Results showed that disease incidence and lesion diameter in mature pears from trees sprayed with ASM for three times during growth and inoculated with Penicillium expansum or Alternaria alternata after harvest were 27.9 and 42.7%, or 29.1 and 23.4% lower, respectively, than in control fruit 17 days after inoculation. Mature fruit from ASM-treated trees exhibited higher activities of defense enzymes including phenytalanine ammonia-lyase (PAL), chitinase and beta-1,3-glucanase than in control at harvest. In young pears, activities of peroxidase, polyphenoloxidase, PAL, chitinase and beta-1,3-glucanase were significantly enhanced by ASM after first spray on trees. The ASM spray also significantly increased H2O2 level and glutathione reductase activity, but reduced activities of catalase and ascorbate peroxidase in young pears. The study indicated that enhancement of disease resistance in harvested Yali pear fruit could be the result of multiple effects of several factors related to plant defenses induced by ASM sprays on trees during fruit growth. Application of ASM in the field holds great promise for controlling postharvest diseases of the fruit. (c) 2006 Elsevier B.V. All rights reserved.