Macro- and microelement fertilizers influence the severity of Fusarium crown and root rot of tomato in a soilless production system

Host nutritional variables were evaluated for their effects on the severity of crown and root rot of tomato caused by Fusarium oxysporum f.sp. radicis -lycopersici. Tomato (Lycopersicon esculentum Mill.) seedlings (cv. Bonnie Best) were grown in a pathogen-infested, soilless rockwool system in the gr eenhouse and were fertilized with a nutrient solution that was amended with macro- and microelements at various rates. Disease was evaluated after 2 w eeks using an index of 0 to 4, and plant fresh weight was measured. Regress ion analysis indicated that disease severity was significantly increased by ammonium-nitrogen [NH4Cl, (NH4)(6)Mo7O24, and (NH4)(2)SO4], NaH2PO4. H2O, Fe-EDDHA, MnSO4, MoO3, and ZnSO4. 7H(2)O. Disease severity was reduced by n itrate-nitrogen [Ca(NO3)(2). 4H(2)O] and CuSO4. H2O. Low rates of NH4NO3 (3 9 to 79 mg . L-1 N) reduced disease, but rates above 100 mg . L-1 N increas ed it. Disease was not affected by MgSO4. 7H(2)O. In all cases, plant growt h was inversely related to disease severity. Mineral fertilizers had no eff ect on nutrient solution pH. This information sheds new light on environmen tal factors that influence plant-pathogen interactions, and may be applied to develop a management strategy for Fusarium crown and root rot based on h ost nutrition.