BIOCHEMICAL-STUDIES ON THE CELL-WALL DEGRADATION OF FUSARIUM-OXYSPORUM F-SP LYCOPERSICI RACE-2 BY ITS OWN LYTIC ENZYMES FOR ITS BIOCONTROL

An exhaustive cell wall fractionation of Fusarium oxysporum f. sp. lycopersici race 2 (Fol2) with alkali in a sequential procedure yields only three polysaccharide fractions: Fl(S) (alkali and water soluble), Fl(I) (alkali soluble and water insoluble) and F4 (alkali-insoluble residue). These fractions amounted respectively to 15, 1.3 and 52% of the cell wall and have been characterized by infra-red spectroscopy and gas liquid chromatography-mass spectrometry (GLC-MS). Fl(S) is a beta-gluco-galacto-mannan, Fl(I) is mainly composed of a beta-1,3-glucan and F4 is a beta-1,3-glucan-chitin complex. The Fl(S) is a very complex polysaccharide and its hydrolysis requires the action of different enzymes. The lysis of the cell wall and its three fractions with lyric enzymes from Fol2 has been studied and a correlation between the lysis of the cell wall and the lysis of these fractions was found. The amount of glucose, galactose and mannose in Fl(S) and cell wall hydrolysates were quantified by GLC and they indicated the hydrolysis of the gluco-galacto-mannan polysaccharide. In the hydrolysis of F4 and cell walls N-acetylglucosamine was also found and quantified. When chlamydospores of this fungus were treated with Fol2 lyric enzymes, the sugars liberated were principally mannose and N-acetylglucosamine. These results indicate that Fol2 produces during its autolysis the necessary enzymes to hydrolyse its own cell walls. This fact suggests that a biological control of Fol2 with its own lyric enzymes, conveniently immobilized, could be developed.