Testing the effect of routine fungicide application on ectomycorrhiza formation on Pinus halepensis seedlings in a nursery

The fungicides benomyl, captan, hymexazol, iprodione, propamocarb hydrochloride and thiram were applied in a combined schedule to Pinus halepensis seedlings grown under nursery conditions to study their effect on mycorrhiza formation and plant growth. The inoculated fungi Pisolithus tinctorius (strains 3SR and Mx) and Lactarius deliciosus formed mycorrhizas when fungicides were applied. However, fungicide application led to a significant decrease of mycorrhizal plants with Pisolithus tinctorius strain 3SR (from 62% without fungicides to 35% with fungicides). This effect could be attributed to a direct effect of fungicides on mycelial growth. The morphometric and nutritional parameters were very similar in plants treated with or without fungicides, and no differences on sanitary status of plants were noted. The use of preventive fungicide treatments in plant production, which may have a harmful effect on the environment, is therefore questioned.