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A Fluorescent Technique for Studying Growth of Peronospora tabacina on Leaf Surfaces. Yigal Cohen, Professor, Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52 100, Israel; Sara Pe’er(2), Orly Balass(3), and Michael D. Coffey(4). (2)(3)Graduate students, respectively, Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52 100, Israel; (4)Professor, Department of Plant Pathology, University of California, Riverside. Phytopathology 77:201-204. Accepted for publication 8 July 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-201.

Calcofluor was used as a fluorescent nontoxic stain to study germination, appressorial formation, vesicle production, and sporulation of Peronospora tabacina on leaf surfaces. Fungal germination proceeds equally well on leaves of tobacco, pepper, tomato, and potato but not on Nicotiana debneyi in which germ tubes were abnormal and appressorial formation was inhibited. In tobacco, appressorial formation decreased with increasing plant age and gradually decreased in younger leaves of older plants. In tobacco, appressorial formation was not affected as long as 21 days after stem inoculation with P. tabacina but was inhibited at 30 days. Germination and appressorial formation in tobacco were not affected by metalaxyl but were strongly inhibited by β-ionone. The technique is simple, rapid, and reliable and can be used to study effects on fungal ingress in situ of plant genotypes, toxicants, and environmental factors.

Additional keywords: microscopy, resistance.