Correlation between hydrolytic enzyme activities measured in bean seedlings after Trichoderma koningii treatment combined with pregermination and the protective effect against Pythium splendens

An experimental protocol consisting in the colonisation of pregerminated bean seeds dressed with Trichoderma sp. was used in order to study the mechanisms correlated with the protective effect against Pythium splendens. Seed dressed with TH-11 (T. koningii) for 24 h presented a higher protective effect and a higher level of seed colonisation as compared to those dressed with TH-13 (T. longibranchiatum). The levels of seed coat colonisation by TH-11 and TH-13 was shown to be correlated with the carboxymethylcellulase activity, as measured in the seed coats retreived from germinating dressed bean seeds. The seed coat colonisation was also associated with an increased activities of endo-1,3-beta-glucanase and endochitinase measured in seed extracts, and an inhibitory effect of seed extracts on Pythium sporangia germination. Pretreatment of TH-13-dressed seeds with a commercial cellulase improved all parameters mentioned above, thus suggesting a role of cellulase activity in the colonisation process and the linked protective effect. The possible role of hydrolytic enzymes in the protective effects is discussed.