No abstract

No abstract

Sunflower plants were inoculated with a virulent isolate of Sclerotinia sclerotiorum and with the same isolate nutritionally conditioned to produce small amounts of oxalic acid. The preconditioned isolate behaved as hypovirulent. Tomato plants were inoculated with four S. sclerotiorum isolates of increasing virulence. A close correlation among disease severity, accumulation of oxalic acid, decrease in pH and inhibition of polyphenoloxidase in both infected host tissues was demonstrated. Oxalic acid production as an important factor of virulence in S. sclerotiorum is emphasized and its effect on the phenolic metabolism of the host via inhibition of polyphenoloxidase is suggested.

Acetone precipitates from culture filtrates of three isolates of Botrytis cinerea were resolved by isoelectric focusing on polyacrylamide gels to detect differences in the polygalacturonase and protein patterns. Only a few bands -four in the protein patterns and two in the polygalacturonase patterns -were common to all the isolates. Differences were also detected in polygalacturonase and protein patterns of the same isolate at different ages of culture (7, 14 and 2 1 d). Identical polygalacturonase patterns were obtained when isoelectric focusing was applied to an acetone precipitate either directly or after further purification by ion-exchange chromatography.

Extracts of Allium cepa and A. porrum‐ contain factors that inhibit to various extents polygalacturonases (PGs) produced in vitro by Sclerotinia sclerotiorum, Botrytis cinerea, Fusarium moniliforme, Phoma terrestris, Sclerotium cepivorum, Macrophomina phaseolina, Didymella bryoniae andPhoma lycopersici. The PG inhibition rank changed using leek or onion extract. The inhibition factors are possibly proteins, do not present particular specificity and act against PGs of fungi pathogens and non pathogens for these plant species.