VIEW ARTICLE

Resistance

Accumulation of Scoparone, a Phytoalexin Associated with Resistance of Citrus to Phytophthora citrophthora. U. Afek, The Hebrew University of Jerusalem, Department of Plant Pathology and Microbiology, Faculty of Agriculture, P. O. Box 12, Rehovot 76100; A. Sztejnberg, The Hebrew University of Jerusalem, Department of Plant Pathology and Microbiology, Faculty of Agriculture, P. O. Box 12, Rehovot 76100. Phytopathology 78:1678-1682. Accepted for publication 18 July 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1678.

Citrus species resistant and susceptible to Phytophthora citrophthora were compared for production of scoparone in the bark 1–8 days after inoculation with the pathogen. Concentrations of scoparone were higher (maximum 440 μg/g fr wt after 4 days) and increased more rapidly in the resistant species within 24 hr after inoculation. In the susceptible species the maximum concentration was 41.6 μg/g fr wt. The lesion length caused by P. citrophthora in citrus bark 4 days after inoculation was 2.5–5.0 mm in the resistant, compared with more than 11 mm in the susceptible. Scoparone inhibited mycelial growth of P. citrophthora and spore germination of six other phytopathogenic fungi in vitro. Radioactivity was incorporated into scoparone in infected citrus bark that had been treated with ¹⁴C-phenylalanine. Resistant citrus species, treated with the inhibitor aminooxyacetic acid (AOA) before inoculation, became susceptible to P. citrophthora.