Abstract
Twenty-three isolates of Verticillium albo-atrum, sixteen of V. dahliae, two of V. tricorpus, four of V. nigrescens and one of V. nubilum, all produced endopoly-galacturonase (PG), pectin trans-eliminase (PTE) and pectin methylesterase (PME) in amounts that varied as much within species as between them. Maximal production of viscosity-reducing enzymes occurred after 7 days, with peaks of activity at approximately pH 5·0 and 9·0; the former was attributed to the action of endo-PG, and the latter coincided with the optimal pH of PTE. Production of PTE and PG was constitutive but was increased by the presence of pectin in the medium. PME was produced in a pectin-glucose-salts medium but not in a potato extract-pectin medium. Pectic enzyme production and virulence were not closely correlated, although there was some suggestion with the hop isolates of V. albo-atrum that higher PME and PG production was associated with high virulence. When isolates of V. albo-atrum or V. dahliae, grown on pectin-glucose-salts medium, were ranked according to PG or PME activity they tended to fall into groups having in common the species, variety or locality of the host from which they were isolated.
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