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Histological Changes in the Roots of an Avocado Cultivar, Duke 7, Infected with Phytophthora cinnamomi. Darren Phillips, School of Botany, University of Melbourne, Parkville 3052 Australia; B. R. Grant(2), and Gretna Weste(3). (2)Russell Grimwade School of Biochemistry, University of Melbourne, Parkville 3052 Australia; (3)School of Botany, University of Melbourne, Parkville 3052 Australia. Phytopathology 77:691-698. Accepted for publication 6 October 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-691.

Roots of the moderately resistant avocado cultivar, Duke 7, formed limited lesions when inoculated with the fungal pathogen, Phytophthora cinnamomi. Histological examination of tissue changes revealed two distinct anatomical responses at the lesion boundary; the formation of necrophylactic periderm in the cortex and whorls of cells walling off infected phloem bundles in the stele. Necrophylactic periderm divided necrotic, infected tissue from nonnecrotic, uninfected cortical tissue from the epidermis through to the endodermis and always coincided with the very rapid disappearance of infected cortical tissue. Phloem bundles, the site of intensive hyphal colonization in lesioned tissue, were devoid of hyphae after the formation of cell whorling and cell wall thickening at the lesion boundary. These anatomical responses appear to be an important component in determining the resistance response of this rootstock.