01354naa a2200133 a 450000100080000000500110000800800410001910000130006024501120007326000060018552009550019170000190114677300550116516462581993-06-07               bl ---       0--  u    #d1 aAFEK, U.  aAccumulation of Scoparone, a Phytoalexin Associated with Resistance of Citrus to Phytophthora citrophthora.  c0  aCitrus 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 (maximim 440 mg/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 mg/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 incorprated into scoparone in infected citrus bark that had been treted with ^14 C-phenylalanine. Resistant citrus species, treated with the inhibitor aminooxyacetic acid )AOA) before inoculation, became susceptible to  P. citrophthora.1 aSZTEJNBERG, A.  tThe American Phytopathological Sciety, p.1678-1682