The relationships between in vitro production of cell wall-degrading enzymes and aggressiveness of three Phaeosphaeria nodorum isolates were investigated. When grown in liquid medium containing 1% cell wall from wheat leaves as the carbon source, the isolates secreted xylanase, a-arabinosidase, b-xylosidase, polygalacturonase, b-galactosidase, cellulase, b-1,3-glucanase, b-glucosidase, acetyl esterase and butyrate esterase. Time-course experiments showed different levels of enzyme production and different kinetics between isolates. A highly aggressive isolate produced more xylanase, cellulase, polygalacturonase and butyrate esterase than did the two weakly aggressive isolates. Xylanase was the most active polymer-degrading enzyme produced, suggesting a key role during pathogenesis by P. nodorum.

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In this study, two Mycosphaerella graminicola isolates produced a range of cell wall-degrading enzymes (CWDE) in vitro that can potentially degrade wheat cell walls. The influence of three carbon sources on CWDE in vitro production was tested: 1) 1 % galactose (w/v), 2) 1% wheat cell walls (w/v) and 3) a mixture of 1% galactose (w/v) and 1% wheat cell walls (w/v). Six major activities produced by both isolates were detected: xylanase, b-1,3-glucanase, polygalacturonase, cellulase, b-xylosidase and b-galactosidase. Time-course experiments showed that different levels of enzyme activities were obtained with isolates 323 and 94269. These activities levels varied also with the type of carbon source used. Principal Component Analysis showed that the enzyme activities are gathered into two groups. None of the activities of the first group was correlated to the activities of the second group. It also showed that the optimal medium that allowed the production of most of the major activities contained both galactose and wheat cell walls.