Possible role of colonization and cell wall-degrading enzymes in the differential ability of three Ulocladium atrum strains to control Botrytis cinerea on necrotic strawberry leaves

Ulocladium atrum (strain 385) consistently reduced Botrytis cinerea sporula tion on necrotic fragments of strawberry leaves. On these tissues, two stra ins of U. atrum (isolates 18558 and 18559) showed lower antagonistic activi ties than the reference strain 385. Colonization of strawberry leaflets by the three U. atrum strains appeared similar in the absence of B. cinerea, w hether quantified by chitin or immunological assays. The second method (bas ed on anti-U. atrum antibodies) revealed that strawberry leaflet colonizati on by U. atrum 385 was better than by the other U. atrum strains in the pre sence of A cinerea. An immunoassay using anti-B. cinerea antibodies reveale d that the colonization of B. cinerea in tissues was lower in the presence of U. atrum 385 than with the two other U. atrum strains. The enzymatic act ivities produced by U. atrum 385 during the colonization phases of necrotic tissues were compared to B. cinerea and U. atrum strains 18558 and 18559. U. atrum 385 had the highest lipase, pectate lyase, and cellobiase activiti es while B. cinerea had the highest endo-beta -1,4-glucanase activity. The study of lytic activities hydrolyzing the fungal cell wall revealed higher beta -1,3-glucanase activity with U. atrum 385, which was stimulated by B. cinerea on necrotic strawberry leaflets. These results suggest that plant a nd fungal cell wall-degrading enzymes produced by U. atrum 385 may play a c omplementary role in the competitive colonization of dead strawberry leaves against B. cinerea.