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Types of Germination and Differentiation of Vesicles by Basidiospores of Cronartium ribicola. Everett M. Hansen, Former Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706, Present address of senior author: Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; Robert F. Patton, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 65:1061-1071. Accepted for publication 16 April 1975. DOI: 10.1094/Phyto-65-1061.

Germination of basidiospores of Cronartium ribicola on artificial substrates and eastern white pine needle surfaces resulted in various types of germ tube growth and development. In what was considered normal germination, one to several thin germ tubes, 1-3 µm in diameter, grew from each spore. Only one continued to elongate, usually reaching a length of 100-300 µm, and occasionally forming one or two short branches. Germ tubes usually grew along the surface of the substrate, but in moisture chambers often grew into the air from both needles and artificial substrates. Elongation was greatest between 9 and 15 C, but dropped sharply at higher temperatures. Intercalary or terminal swellings (vesicles) often were developed, which closely resembled the infection vesicle that was produced in the substomatal chamber during successful needle penetrations. On collodion membranes at 16 C, less than 5% of germ tubes differentiated vesicles. Fluctuating temperatures, high temperature (28 C) shocks of 1 or 2 hours duration, and changes in osmotic concentration of a supporting solution, significantly increased the proportion of vesicles formed. The duration of incubation at 16 C prior to temperature shock affected both the number and type (terminal or intercalary) of vesicles. Vesicle formation was hypothesized to be a result of disrupted growth following a change in the germ tube environment. Basidiospores associated with water droplets usually formed thick (3- to 5-µm) germ tubes or sterigmata and secondary basidiospores. Sometimes a zigzag type of germ tube growth occurred, characterized by an angular pattern of the main germ tube axis and the presence of numerous short side branches. Such development was induced by a volatile substance associated with germinating spores and was modified by the nature of the substrate and an unknown factor associated with the time of year. Zigzag growth prevented vesicle formation, reduced effective germ tube length, and inhibited nuclear migration and division.

Additional keywords: spore germination, white pine blister rust, zigzag growth, secondary spores.