Selection and characterization of pectinase-deficient mutants of the vascular wilt pathogen Verticillium albo-atrum

Three putative pectinase-deficient mutants of the vascular parasite Verticillium albo-atrum which produced, 3, 9 and 43% of wild type pectin lyase were isolated on solid selection media specific for polygalacturonase and pectin lyase detection. The mutants (which were identical to the wild type in growth, morphology and sporulation, apart from 34i which grew poorly on pectic polymers) were grown on pectin, host cell walls, galacturonic acid and glucose to determine changes in production and regulation of pectin lyase, polygalacturonase, cellulase (Cx), β-d-galactosidase, β-d-glucosidase and l-leucine arylamidase. Analysis of culture fluids revealed isolate C23 to be defective in secretion of all enzymes and pectin lyase accumulated intracellularly; isolate 34i was unable to utilize galacturonides and was therefore jointly deficient in production of inducible polygalacturonase and pectin lyase. Analysis of isozyme patterns revealed that mutant 24d produced reduced levels of five of the six pectin lyase isozymes.