RESUMO
The most important plant species employed in reforestation programs depend on ectomycorrhizal fungi for their establishment and growth. The exploitation of this symbiosis to improve forest productivity requires fungal inoculants in a large scale level. To develop such a technology it is necessary to define the optimal composition of the culture medium for each fungus. With these objectives in mind, the effect of the composition of the culture medium on biomass production of the ectomycorrhizal fungus Pisolithus microcarpus (isolate UFSC-Pt116) was studied. The original composition of two culture media, already employed for cultivation of ectomycorrhizal fungi, was submitted to several variations with the C/N ratio as the main variable. A variation of the Pridham-Gottlieb medium was the most efficient for the production of biomass. Therefore, it was submitted to a factorial assay where glucose, peptone and yeast extract components were the factors analyzed. Results showed that the glucose concentration may be increased up to 40 percent in order to promote higher biomass production. Peptone had a positive effect on this variable, whereas yeast extract promoted a deleterious effect. These results indicate that it is advisable to eliminate yeast extract from the medium and replace it with peptone prior to use.
RESUMO
The viability and infectivity of an ectomycorrhizal inoculum (isolate UFSC-Rh90, Rhizopogon nigrescens), produced by submerged cultivation in an airlift bioreactor and immobilized in beads of calcium alginate gel, was studied. Inoculum remained 100 percent viable after 18 months in a 0.85 percent NaCl solution at 8 ± 1°C. Mycelium grew from the beads after 48 h when they were placed on a solid culture medium at 25 ± 1°C. Viability of pellets of non-immobilized mycelium stored under the same conditions decreased gradually after the third month of storage, reaching 0 percent by the 12th month. These pellets presented a gradual darkening, which was more intense in those located near the surface of the NaCl solution. In culture medium, these dark pellets showed no viability. Gel immobilization helps to maintain mycelium viability during storage and offers a physical protection when the inoculum is applied to the planting substrate. After eight months refrigeration, the immobilized inoculum was still able to infect Pinus taeda seedlings, colonizing an average of 37 percent of the root tips when inoculated in the plant growth substrate under greenhouse conditions. This inoculum presents a commercial potential to be produced and applied in forest nurseries.
Estudou-se a viabilidade e a infectividade de inoculante fúngico ectomicorrízico (isolado UFSC-Rh90, Rhizopogon nigrescens), produzido através de cultivo submerso em biorreator airlift e encapsulado em gel de alginato de cálcio. O inoculante permaneceu viável após 18 meses em solução de NaCl (0,85 por cento) a 8 ± 1°C. O micélio emergiu dessas cápsulas após 48 h de incubação a 25 ± 1°C em meio de cultura sólido. A viabilidade dos pellets de micélio não imobilizado, armazenados sob as mesmas condições, reduziu-se gradualmente após três meses de armazenamento e atingiu 0 por cento aos 12 meses. Esses pellets apresentaram um escurecimento gradual que foi mais intenso naqueles localizados próximos à superfície da solução de NaCl. Em meio de cultura, os pellets escurecidos mostraram-se inviáveis. A imobilização em gel mantém a viabilidade do micélio durante o armazenamento, além de oferecer uma barreira física quando aplicado ao substrato de plantio. Após oito meses de armazenamento sob refrigeração, o inoculante imobilizado colonizou uma média de 37 por cento das raízes curtas de mudas de Pinustaeda, quando aplicado ao substrato de plantio sob condições de casa-de-vegetação. Esse inoculante apresenta potencial para produção comercial e aplicação nos viveiros florestais.