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Pisatin Production in Powdery Mildewed Pea Seedlings. H. Oku, Professor, Laboratory of Plant Pathology, College of Agriculture, Okayama University, Tsushima, Okayama 700, Japan; S. Ouchi(2), T. Shiraishi(3), and T. Baba(4). (2)(3)(4)Associate Professor, Instructor, and Graduate Student, respectively, Laboratory of Plant Pathology, College of Agriculture, Okayama University, Tsushima, Okayama 700, Japan. Phytopathology 65:1263-1267. Accepted for publication 9 June 1975. DOI: 10.1094/Phyto-65-1263.

An antifungal principle isolated from powdery mildewed seedlings of pea was identified as pisatin by physico-chemical analyses. Pisatin was first detected 2 days after inoculation of leaves with the pathogenic powdery mildew fungus, Erysiphe pisi at a concentration of 3 µg/g fresh weight and then increased logarithmically, reaching 300 µg/g fresh weight by 4th day. When inoculated with a nonpathogenic fungus, E. graminis hordei, pisatin was detected much earlier, 15 hours after inoculation, although concentration was low (0.3 µg/g fresh weight). The conidia of the pea pathogen, E. pisi were 13 times more tolerant to pisatin than those of the nonpathogen, E. graminis hordei; the ED₅₀ for conidia germination was 530 µg/ml for E. pisi and 40 µg/ml for E. graminis hordei.