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Spore Germination and Mode of Cotton Infection by Ramularia areola. Y. Rathaiah, Laboratoire de Pathologie végétale, Institut National Agronomique Paris-Grignon, 78850-Thiverval-Grignon, France, Present address: Scientist in Plant Pathology, Regional & District Research Station, Diphu-782460, Karbi Anglong District, Assam, India; Phytopathology 67:351-357. Accepted for publication 27 April 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-351.

Conidia of Ramularia areola germinated at temperatures ranging from 16 to 30 C, but the most rapid germination and germ tube development occurred at 25-30 C. Germination and germ tube development were greatly decreased at high spore concentrations. Host penetration by this pathogen was studied under (i) nightly wetting and day drying and (ii) continuous wetting regimes. Excellent penetrations, almost always accompanied by appressorium formation, occurred under nightly wetting and day drying. Severe infection occurred after four consecutive nightly wettings (48 hours) interrupted by daytime drying. Under a regime of continuous wetting there was little penetration and appressoria were not formed. Circumvention of stomatal opening by a germ tube prior to penetration was frequent under continuous wetting. Precocious sporulation of conidial inoculum occurred. Resumption of germ tube growth after the drying period was regulated by the relative humidity of the drying atmosphere.

Additional keywords: Cercospora musae, C. beticola, rust fungi.