This work was conducted to elucidate the pH effect on the conidia germination and on the mycelium growth of F. oxysporum f. sp. lycopersici and the effect of N sources on the infection process of the tomato (Lycopersicon esculentum) roots. Initially, the quantification of conidia germination and the mycelium growth were performed in liquid culture medium with pH ranging from 2,0 to 11,0. The medium pH at 14 day after fungi growth was also measured. Cultivar 'Kada Gigante' was grown in a nutrient solution containing three N sources, NH4+, NO3- and NH4NO3, with or without addition of Fusarium conidia in the solution. The solution pH, root morphological alterations and pathogen colonization were measured up to 240 h after infestation. N-NO3- application resulted in higher pH values and favored root development, with significant increase of root hair number. It also reduced the conidia attachment rate and Fusarium colonization rate compared to N-NH4NO3 and N-NH4+. These results are mostly due to the ionic imbalance of N-NH4+ fed plants than to the single rhizospheric pH change pH. The pathogen was able to develop on a wide range of pH - 3,0 to 9,0 in medium culture.
fusarium wilt; rhizosphere; NO3-; NH4+
