COMPARISON OF INOCULATION METHODS WITH MYCOSPHAERELLA-BRASSICICOLA ONBRASSICA-OLERACEA VAR CAPITATA - ASCOSPORES VERSUS MYCELIAL FRAGMENTS

Ascospores can be collected from dried leaves of white cabbage from th e previous season, carrying lesions of the fungus. Discharge of ascosp ores is stimulated by light and takes place within a broad temperature range (5-20-degrees-C) under humid conditions. A method is described to isolate single ascospores, or to collect sufficient ascospores for small inoculation experiments. In order to screen large numbers of pla nts under controlled conditions, mycelial fragments can be used as ino culum. Using mycelial fragments requires a long (4-5 days) duration of leaf wetness necessary for infection. Ascospores infected the host pl ant with a much shorter duration of leaf wetness (< 2 days). The resul ts of this study show that the use of mycelial fragments as the inocul um type in infection studies may lead to erroneous conclusions and fal se recommendations. Results of inoculation with ascospores indicate th at the minimum humidity requirement for infection in the field is lowe r (< 2 days) than generally assumed, and that the temperature range fo r infection by ascospores is at least 10-20-degrees-C.