Fermentação líquida como estratégia para produção massal de conídios de Trichoderma

Abstract

The demand for biological products for the control of plant diseases is in constant growth. Among the main agents for the biocontrol of plant diseases, the Trichoderma spp. is prominent. The commercial products based on this antagonist are obtained by means of the fermentation in solid medium, which, despite presenting good quality spores, cannot meet the demand and is presented with lack of standardization. Fermentation in liquid medium is a more adequate method when compared to solid medium for the large-scale production of Trichoderma spp. In this work, the objective was to optimize the combination of variables that interfere in the production process of Trichoderma asperellum conidia, making its production in liquid medium feasible. Trials in Erlenmeyers were used to establish the best condition and composition of factors: pH, photoperiod, temperature, C:N relation and water activity for the production of conidia, colony forming units and increment of fungal biomass of the LQC-96 T. asperellum isolate. After optimization of the cultivation medium, the growth curve of the LQC-96 isolate was established, and new Trichoderma spp. isolates were tested under these conditions. Erlenmeyers of 250 mL of capacity, containing 90 mL of modified Czapek-Dox medium and 10 mL of T. asperellum inoculum suspension (3 x 106 conidia mL-1) were used. The Erlenmeyers were maintained in orbital agitation at 160 rpm under different temperatures and photoperiods, for seven days. After this period. the number of conidia in the suspension and the dry biomass weight were evaluated, also determining the number of colony forming units (CFU). Each Erlenmeyer represented a distinct treatment, submitted to the different levels of factors, as determined by the Plackett-Burman design (PB 12) and, posteriorly, by the Rotational Central Composite Design (RCCD). Of the five variables tested, only pH and C:N relation were significant to the production of conidia and submitted to the second design. The remaining variables were fixed. The best conditions for the production of T. asperellum conidia by liquid fermentation were under initial pH of 3.5 and C:N relation of 200:1, at 30oC, with no glycerol and under light for 24 hours. In addition to the conidia, the production of chlamydospores. The highest concentration of conidia was observed after seven days of agitation. The Trichoderma erinaceum isolates, T12 and T18, and T. harzianum isolate, T15, also produced high concentrations of conidia (108 conidia mL-1) under optimized conditions.