Cell wall degrading enzymes and their impact on Fusarium proliferatum pathogenicity

Fusarium proliferatum is one of the most pathogenic Fusarium species on date palm worldwide. We evaluated the colonization ability of 42 F. proliferatum strains collected from date palm trees with disease symptoms on detached leaflets of cvs Sheeshee and Sukkary. Cell wall degrading enzyme (CWDE) production by these strains was assessed with multiple relative enzyme activity (RA) indices. The ability of F. proliferatum strains to colonize leaflet cuttings varied, and there were significant differences (P < 0.05) in susceptibility between the Sheeshee and Sukkary cvs. All F. proliferatum strains tested could hydrolyze carboxymethylcellulose (CMC), citrus pectin and starch, with different capabilities. RA indices calculated from direct assessment of halo zones were consistent with fungal strain colonization ability, but ratio-based RA indices were not. Based on RA(4) index of cellulases, F. proliferatum strains were divided into three groups. The first group (33% of strains) showed very strong reaction in hydrolysing CMC, the second group (62% of strains) showed strong reaction in hydrolysing CMC, and the third group (5%) showed moderate reaction in hydrolysing CMC. Most strains had moderate pectin-hydrolysis activities. Starch-hydrolysis activities ranged from weak to strong. Overall, there was a positive correlation between cellulase production and a strain's colonization ability. Thus, CWDEs produced by F. proliferatum play a role in the colonization of date palm leaflets and hence may be important pathogenicity factors.