A comparative study of certain soil-borne cereal pathogens with reference to carbohydrate utilisation and polysaccharide hydrolysis
Cochliobolus sativus, Fusarium culmorum and Gaeumannomyces
graminis var tritici isolates produced pectin degrading enzymes,
xylanase and carboxymethylcellulase when grown in a salts medium
with an appropriate carbon source. There was little difference
in the amounts of enzymes produced by the organisms except for
the greatly enhanced endo-poly-rnethylgalacturonase activity when
F. culmorum was grown with citrus pectin as the carbon source.
When grown on powdered wheat straw xylanase and carboxymethylcellulase
activities were not present until the late stages of incubation
,~ereas pectin degrading enzyme activity appeared at an early stage.
Absence of phosphate from culture meduim did not prevent the production
of pectin degrading enzymes by F. culmorum and C. sativus although
its presence influenced early enzyme production. Low nitrate
concentrations did not preclude cell wall polysaccharide degrading
ernzymes production. Multiple forms of pectin degrading enzynes were
produced by F.culmorum and C. sativus when grown on citrus pectin and
and sodium polypectate.
Uptake of glucose fram the culture medium by F culmorum was
fastest, C. sativus was slowest and G. graminis var tritici was
intermediate irrespective of nitrate concentrations. Low levels of
nitrate in culture medium drastically reduced the uptake of glucose
by C. sativus: slightly reduced that of G. graminis var tritici
isolates but increased rate of uptake by F. culmorum.
It is suggested that degradation of pectin and xylan and the
utilisation of the degradation product may be as important as
cellulolysis in the saprophytic survival of these organisms