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Physiology and Biochemistry

Relationship of Wound-Induced Peroxidase Activity to Epicarp Lesion Development in Maturing Pistachio Fruit. R. M. Bostock, Assistant professor, Department of Plant Pathology, University of California, Davis 95616; C. S. Thomas(2), J. M. Ogawa(3), R. E. Rice(4), and J. K. Uyemoto(5). (2)(3)(5)Postgraduate research assistant, professor, and visiting scientist, respectively, Department of Plant Pathology, University of California, Davis 95616; (4)Professor, Department of Entomology, University of California, Davis 95616. Phytopathology 77:275-282. Accepted for publication 23 July 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-275.

Needle-puncture through the pericarp of maturing pistachio (Pistacia vera) fruit induced symptoms similar to those observed in fruit with epicarp lesion after insect feeding. Mechanical or insect wounds through the pericarp markedly stimulated peroxidase activity (as much as 3- to 10-fold relative to unwounded fruit) in the fruits of cultivars Kerman and Trabonella. The induced peroxidase activity was apparent histochemically within 24 hr of wounding, before symptom development, and at a distance several millimeters from the wound site. Penetration of the inner surface of the endocarp was essential for stimulation of peroxidase activity and lesion development. Both events were inducible during April and May but that capability diminished after the onset of endocarp lignification. Wounding induced at least three cathodic isoperoxidases not present in unwounded fruit. Gallic acid, methyl gallate, and other gallotannins were the principal phenols present in ethanol extracts of the pericarp and their concentrations declined early in the season. The data indicate that injury to the endocarp is essential for symptom expression and are consistent with the hypothesis that epicarp lesions result from the wound-induced peroxidation of components in the pericarp.