Sexual recombination in Phytophthora cinnamomi in vitro and aggressivenessof single-oospore progeny to Eucalyptus

Fifty single oospore progeny were established from an in vitro mating of A1 and A2 mating type isolates of Phytophthora cinnamomi from South Africa. F orty-nine progeny were identified as F-1 hybrids using seven random amplifi ed polymorphic DNA (RAPD) primers, and one was a selfed isolate of the A1 m ating type parent. Among the hybrid progeny, 24 and 25 were A1 and A2 matin g type, respectively. Aggressiveness of progeny and parental isolates was a ssessed on 1-year-old seedlings of Eucalyptus smithii. The mean aggressiven ess of hybrid oosporic isolates, expressed as lesion length, was significan tly (P = 0.0001) lower than that of the parental isolates. No significant d ifference in aggressiveness of A1 and A2 mating type F-1 hybrid isolates wa s observed. This is the first report demonstrating sexual recombination in vitro in P. cinnamomi.