HETEROTHALLISM AMONG SOUTH AUSTRALIAN CLONAL LINES OF UNCINULA NECATOR

The existence of two mating types and heterothallism among South Austr alian clonal lines of Uncinula necator was confirmed. An in vitro mati ng system for U. necator was established for identifying mating type a nd for future use in genetic studies. Cleistothecia, containing viable ascospores, formed on micropropagated grapevines in vitro following c o inoculation of two clonal lines of U. necator of opposite mating typ e. Specific incubation conditions were required, however, for the init iation of cleistothecia. These findings are discussed in relation to p otential mechanisms regulating sexual reproduction. Among 20 clonal li nes from South Australia tested, ten lines were identified as the 'plu s' mating type and seven lines were identified as the 'minus' mating t ype. The mating type of the remaining three clonal lines has not been confirmed. Six of the 17 lines were paired in all possible combination s, and cleistothecia formed in all pairings where they were expected t o occur for a heterothallic ascomycete with two mating types. Ascospor es recovered from these controlled crosses produced typical colonies o f U. necator when germinated on detached grapevine leaves.