O uso do estufim e a sazonalidade na produção de mudas de materiais genéticos recalcitrantes ao enraizamento

Abstract

The general aim of this study is to evaluate the effect of the management of the clonal minigarden on the ministumps productivity indexes, survival, rooting of minicuttings and physiological quality of ministumps related to the species of the genera Corymbia and Eucalyptus. The research was carried out at the CMPC Company – Celulose Riograndense, located in Barra do Ribeiro, RS. The experiment was conducted in a randomized block design in a factorial scheme with subdivided plots, in which the main plot is made up of two types of clonal minigarden management (with and without greenhouse) and in the subplot two clones (Eucalyptus saligna and Corymbia torelliana x Corymbia citriodora). The E. saligna clone, served as a reference in view of being a commercially produced clone. In each collection, the productivity assessment of the ministumps was carried out. At 30 days after staking, survival was evaluated and at 45 days the percentage of rooting of the minicuttings. In parallel, the minicuttings were evaluated for the production of hydrogen peroxide (H2O2). In all seasons, the environmental variables of temperature and relative humidity were evaluated.The greenhouse promoted an increase in temperature and relative humidity in all evaluated seasons. The ministumps of the hybrid C. torelliana x C. citriodora, when conducted in a greenhouse, showed an increase in productivity (minicuttings/m²/month) in all seasons, a result that was less evident for E. saligna. In addition, the productivity of the hybrid is significantly higher than that of the commercial clone E. saligna. After driving to rooting, survival is reduced, mainly, in the warmer seasons, in this case with greater intensity for the hybrid clone. Consequently, the rooting of this genetic material was significantly reduced in the summer, when the cuttings were collected at MJC Ce. On the other hand, in the winter, cuttings collection at MJC Ce is favorable to the rooting of both clones, although the low rate of the hybrid does not allow it to be considered a commercial clone (minimum rooting  60%). The reduction in temperature, associated with increased rooting, are indicative that high temperatures are less favorable for collection and that the use of the greenhouse should be part of the management during the low temperature period (winter), regardless of the clone. In general, the results suggest that, in subtropical regions, the use of greenhouses should be prioritized in the six months with the lowest temperatures, and not necessarily according to the season, a period in which the temperature variation is wide. Technically, it is recommended to use the greenhouse for the production of seedlings via minicuttings, under lower temperatures, for both clones, as a way to enable greater yield of seedlings available for dispatch.