Heterothallism among South Australian clonal lines of Uncinula necator

The existence of two mating types and heterothallism among South Australian clonal lines of Uncinula necator was confirmed. An in vitro mating system for U. necator was established for identifying mating type and for future use in genetic studies. Cleistothecia, containing viable ascospores, formed on micropropagated grapevines in vitro following co-inoculation of two clonal lines of U, necator of opposite mating type. Specific incubation conditions were required, however, for the initiation of cleistothecia. These findings are discussed in relation to potential mechanisms regulating sexual reproduction. Among 20 clonal lines from South Australia tested, ten lines were identified as the 'plus' mating type and seven lines were identified as the 'minus' mating type. The mating type of the remaining three clonal lines has not been confirmed. Six of the 17 lines were paired in all possible combinations, and cleistothecia formed in all pairings where they were expected to occur for a heterothallic ascomycete with two mating types. Ascospores recovered from these controlled crosses produced typical colonies of U. necator when germinated on detached grapevine leaves.