Fusarium oxysporum f. sp. radicis-lycopersici (FORL) is a problematic soil-borne pathogen that is widely reported to cause severe losses in tomatoes. Studies on the use of trace elements to suppress different F. oxysporum biotypes and various other soil-borne diseases has yielded contrasting results. This study was carried out to analyze differential response of FORL to different ZnNO3 concentrations. Four concentration levels of ZnNO3: 0, 86, 172 and 258 mg/ml were investigated. Malt Extract

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... ar media plated petri dishes were infused with 1 ml of the respective four ZnNO3 concentrations These treatments were replicated three (3) times making a total of twelve experimental units. Ten (10) mm diameter mycelial discs of FORL were placed at the center of each of respective experimental units. Mycelial growth in the experimental units incubated at 27 0 C was assessed by measuring mycelial discs diameters. The mycelial radial growth assessment indicated a general trend of increasing growth inhibition with increasing ZnNO3 concentration. Regression analysis was carried out to determine statistically significant differential response of FORL to different ZnNO3 concentrations. There were statistically significant responses (P<0.05) to ZnNO3 concentrations, with LC50 established at 170mg/ml. As this LC50 was established based on FORL it would not assumed to be the same for other FO biotypes. There is therefore the need to establish LC50 for the various FO biotypes i.e., FOL (races 1,2,3) and the endophytic FO. With Zn reported to have phyto-toxicity effect on some plants at certain levels, it is further recommended that LC50 of ZnNO3 for tomato, and various other vegetable seeds should be determined.