Naturally occurring variation in the inducibility of pisatin demethylating activity in Nectria haematococca mating population VI

Fifty-nine field isolates of Nectria haematococca mating population VI, all of which were able to demethylate pisatin, were assayed for the rate of demethylation over a short time interval after a prior treatment with pisatin. Isolates showed a continuous gradation in their demethylation rates, but all isolates highly virulent on pea demonstrated a measurable rate of pisatin demethylation in response to pisatin. This suggested that regulatory control of pisatin demethylation in N. haematococca might influence the virulence of this organism on pea.

An attempt to identify further differences in regulatory phenotypes, based on differential induction of pisatin demethylating activity by pisatin versus 6-methoxy-1-tetralone (a known inducer of pisatin demethylation), was unsuccessful. However, the time course of pisatin demethylation by freshly harvested mycelium in the absence of a previous pisatin treatment did differ among the isolates tested. The length of the lag period before initiation of pisatin demethylation might be used as an additional parameter to distinguish different regulatory phenotypes in N. haematococca.