Influence of sucrose and medium consistency on in vitro multiplication and photosynthetic pigment profile of Eucalyptus saligna

Resumo

In southern Brazil, Eucalyptus saligna is one of the most cultivated species within the Eucalyptus genus for forest plantations, thanks to genetic improvement programs. Among the primary vegetative propagation methods for recalcitrant genotypes is micropropagation. This study aimed to investigate the effects of two variables in the culture medium on the micropropagation of E. saligna. Nodal segments of 2 cm were introduced into a Murashige and Skoog medium supplemented with 0, 15, 30, and 45 g L^-1 of sucrose, considering two different medium consistencies: semi-solid (7.5 g L^-1 of agar), and liquid with a spherical solid support. The experiment followed a completely randomized design, with eight treatments in a factorial scheme and four replicates, each containing 10 explants. After 30 days, several parameters were measured, including the mortality rate, number of shoots per explant, average shoot length, chlorophyll a, b, and total chlorophyll content. The results indicated that the survival and multiplication rates of explants were higher in the semi-solid medium. In contrast, the liquid medium with solid support proved inefficient, as it failed to establish adequate contact between the explants and the culture medium, compromising the nutrient supply. Generally, survival rates were higher in treatments with increased sucrose concentrations, as higher sucrose levels provide metabolic energy and carbon skeletons essential for the biosynthesis of amino acids, proteins, polysaccharides, and other organic compounds required for growth. Furthermore, the higher sucrose concentration promoted shoot formation, although there was no statistically significant difference among the treatments supplemented with sucrose concentrations of 15, 30, and 45 g L^-1. The higher sucrose concentration resulted in a significantly reduced chlorophyll content in the semi-solid medium.