RESUMO
Although basal medium optimization is a key factor in the success of tissue culture, its mineral composition is frequently disregarded when optimizing in vitro propagation protocols. A previous work on Eucalyptus dunnii micropropagation suggests that excessive callus formation and leaf chlorosis are related to specific nutritional conditions of the basal media. Recently, a novel basal medium based on the mineral nutrient analysis of E. dunnii young stump shoots was developed and successfully tested in plant regeneration and micropropagation of E. dunnii, avoiding all these issues. Considering this basal medium as an ideal growth condition, a mild deprivation of each macro and micronutrient and of the total organic fraction was imposed to E. dunnii in vitro cultures for 30 d. As a result, K, Mg, Mn, Cl, Zn, Mo, Ni or Co deprivation quantitatively affected growth and development of axillary shoots. Moreover, leaf chlorosis and the development of organogenic callus under Fe deficiency, and leaf drop along with shoot tip necrosis under N deficiency were observed. These symptoms suggest that nutrient content in E. dunnii tissues needs to be above 420.3 mg kg-1 for Fe and 27.7 g kg-1 for N to avoid the symptoms of leaf chlorosis and shoot tip necrosis. Additionally, the main role of Mn in quantitative responses and the antagonism between ions, especially for Mg/K and Mg/Zn, were denoted by the multivariate analysis. Overall, these results make a relevant contribution to the optimization of in vitro propagation of E. dunnii and other hard-to-propagate related species.
RESUMO
Com o objetivo de avaliar o controle genético da regeneração direta in vitro a partir de plântulas de Eucalyptus grandis, foram utilizadas sementes de 10 progênies de polinização aberta da população base, origem Atherton, localizada em Anhembi, Estado de São Paulo. Vinte dias de cultivo após a germinação, 196 segmentos distais dos hipocótilos por progênie foram inoculados in vitro num Delineamento em Blocos Completos Aleatorizado Generalizado, com duas unidades experimentais por bloco e sete repetições por bloco, usando a interação blocos por progênie como estimadora do erro experimental. Após 14 semanas de cultivo, foram feitas avaliações da regeneração. Houve diferenças significativas de regeneração entre as progênies (P<0,0001) com extremos de regeneração de 11 por cento a 60 por cento. A herdabilidade no sentido restrito entre as médias das unidades experimentais do caráter foi alta (h2m=0,94), indicando que houve um forte controle genético na regeneração in vitro dentro da população. Houve também alta variabilidade dentro da amostra estudada, assim como um forte efeito do progenitor materno sobre a regeneração.
The genetic control of in vitro direct regeneration was tested on seedlings of ten open-pollinated progenies from the base population of Atherton origin of Eucalyptus grandis at University of São Paulo (Brazil). Seeds were germinated in vitro, after twenty days, distal hypocotyls segments from 196 seedlings per progeny were inoculated in culture media at Generalized Complete Randomized Block Design, with two experimental units per block and seven repetitions, using the interaction blocks by progenies as an estimate of the experimental error. At week 14 from the inoculation bud induction was evaluated. Regeneration among progenies were significantly different (P<0.0001). Regeneration varied from 11 to 60 percent. The narrow-sense heritability between means of experimental units for in vitro regeneration was height. (h2m=0.94), indicating a strong genetic control of the trait within the population and also a high maternal effect. High variability within the study sample was found.
