The invention concerns the use of compounds selected among 1,4 .beta.-D-glucuronans, and/or glycuronic polysaccharides derived from polymers of formula (I), and whereof the number of saccharide units is less than about 30, and/or esters and/or ethers corresponding to polymers of formula (I) or said oligosccahride derivatives, as phytosanitary products in applications related to their activity for amplifying the 1,3 .beta.-D-glucanase enzyme; and/or as biofertilisers in applications related to their activity amplifying the 1,3 .beta.-D-glucanase enzyme, and/or the 1,4 .beta.-D-glucanase, and/or the xyloglucan endotransglycolase.