Soil borne pathogens have become a strong limitation to the cultivation of melons under the prevailing edaphic-climatic conditions of the lower San Francisco River valley. Since control of this group of pathogens using fungicides hás been ineffective, it is necessary to develop alternatives that can be applied to the integrated management of diseases caused by these pathogens. To this end, four isolates of Trichodema sp. were evaluated for their ability to colonise the rhizosphere of melon plants under controlled conditions, and their efficiency in the control of pathogens under field conditions. The experiments were carried out using melon seeds treated with formulations of conidia of the fungi T. harzianum LCB47, T. viridae LCB48, T. koningii LCB49 and T. polysporum LCB50. Under the experimental conditions, the treatments LCB47, LCB48 and LCB49 presented propagule counts in the rhizosphere, statistically similar to one another (of 4.54, 5.81 and 5.66 log10 CFU g-1 root, respectively) and significantly higher than LCB50 (3.21 log10 CFU g-1 root). In the field experiment, it was found that the treatments inoculated with the isolates LCB50 and LCB49, showed an incidence of disease similar to each other (24.7 and 28.6% of symptomatic plants, respectively) and a greater effective control than the others. These treatments resulted in a larger number of plants in the planter at the end of the experiment and a consequently higher fruit yield. Thus, it can be concluded that the isolates, T. koningii LCB49 and T. polysporum LCB50, show potential for use in the biological control of soil pathogens in the melon in the San Francisco River valley.
