Multiple forms of pectin-degrading enzymes produced by intersterile groups P, S and F of Heterobasidion annosum (Fr.) Bref.

The time-course of polygalacturonase (PG) and pectin lyase (PNL) activities shown in vitro by several isolates belonging to the intersterile groups (IGs) S and F of Heterobasidion annosum are reported and discussed in relation to their mycelial growth and the changes in the pH and viscosity of the growth medium they produce. IG-S, characterized by a narrow host range, always produced low levels of enzymatic activity. IG-F grew more abundantly and faster than IG-P and IG-S. In the nutrient medium containing pectin as the sole carbon source. PG activity shown by IG-F per unit of mycelial mass was similar to that of IG-P, but different from that of IG-S; by contrast, the specific PNL activity of IG-F was comparable to that of IG-S, but not to that of IG-P. PG, PNL and pectin methylesterase (PME) activities were separated by non-denaturing isoelectric focusing-polyacrylamide gel electrophoresis; to detect the isozymes, agarose overlays containing the appropriate substrate were stained, in a ruthenium red solution. Each IGs behaved differently from the others, and the variations among them were statistically significant. The isozymatic patterns were also very strongly influenced by the culture period. IG-S, unlike the two other IGs, always showed a single PG band with pI 4.7; an attempt to carry out a partial purification of the PG band with pI 4.7 is shown. The results of the present study open the avenue to obtaining more information about the role of pectinolytic enzymes in the root rot caused by H. annosum.