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Ecology and Epidemiology

Stomatal Tropism of Cercospora beticola in Sugarbeet. Y. Rathaiah, Laboratoire de Pathologie végétale, Institut National Agronomique Paris-Grignon, Centre de Grignon, 78850 Thiverval-Grignon, France, Present address: Scientist in Plant Pathology, Regional & District Research Station, Diphu-782460, Karbi Anglong District, Assam, India; Phytopathology 67:358-362. Accepted for publication 11 May 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-358.

Penetration in sugarbeet by Cercospora beticola was enhanced by interruption of leaf wetting with daily dry intervals of 1 or 6 hours duration; 6 hours of drying was more effective. Three phenomena differentiated the interrupted wetting from continuous wetting: (i) initiation of penetration hyphae from germ tubes over stomata; (ii) production of side branches, directed positively toward stomata, from germ tubes near stomatal openings; and (iii) formation of secondary conidia which subsequently effected penetration. The enhanced penetration under interrupted wetting probably is due to hydrotropism. Frequency of penetration was similar in the resistant and susceptible cultivars, but more leaf spots were produced on the susceptible cultivars.