Abstract
Pectic enzyme production by three formae speciales of Fusarium oxysporum, two of which (f. sp. niveum and melonis) cause vascular wilts and one (f. sp. radicislycopersici) a root rot, was studied in vitro. The two vascular wilt pathogens produced much higher levels of endo and lyase activities than the root rotting pathogen. Endo activity was greatest for the wilt fungi after 7 d during the growth phase when the pH of the medium was still acidic, but it declined thereafter. By contrast the lyase activity reached a peak after 20 d when growth was complete and the pH was alkaline. It then fell rapidly and was undetectable after 22 d. All the pectic activities degraded pectin and sodium polypectate and presented a similar profile during the incubation time studied. The preferred substrates were pectin for endo activity and polypectate for total and lyase activities. The behaviour of the forma specialis suggests that similar enzymes are produced by each taxon.
Published Version
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