Propagation, morphophysiological, and anatomical aspects of Bertholletia excelsa genotypes

Abstract

In recent years, there has been an increasing urgency to recover degraded areas, especially in the Amazon region. This brings to light the interest in using native forest species for this purpose, focusing on the production of quality seeds and seedlings. One of the species that serves this purpose is the Brazil nut tree (Bertholletia excelsa Bonpl.), due to its high plasticity in developing and maintaining itself in different soil and climate conditions, and because of her being endangered, it needs technologies related to the propagation and conservation of genetic material to guarantee its existence. However, the main form of propagation of the species occurs via seeds, which has the limitation of low germination rate, and because it is slow and uneven in the natural environment and in the nursery, mainly due to the integumentary and physiological dormancy of the seed, and fungal contamination. An alternative to this is the in vitro micropropagation of zygotic embryos, which provides a high rate of germination, on a large scale in an aseptic environment. Germination is strongly influenced by genotype, since it is associated with the expression of morphophysiological characteristics of seeds and anatomical leaves. Among the genetic improvement initiatives of the species, some genotypes were generated, of which the 606 and Santa Fé stand out, the first of which stands out due to its characteristics of matrix growth, and the second for the productivity of seeds and fruits. Therefore, this work seeks to identify morphophysiological and anatomical markers that differentiate different genotypes of Brazil nut trees, as well as to investigate more efficient propagation methods for the production of seedlings of the species. For this, seeds of the two genotypes were collected at Amazonas state, and of a wild genotype in the state of Pará, which had their integuments removed, and then were taken to the Laboratory of Plant Physiology and Biochemistry, where their morphophysiological variables were measured, sown in expanded vermiculite, and the zygotic embryos of the 606 and wild genotypes were inoculated in full MS (Murashige Skoog) medium; after the complete seedling, the leaf morphoanatomy was described. As for the morphophysiology, all the genotypes had significant differences, and morphoanatomical differences were also detected in the leaves of the seedlings. Genotype 606 stood out in terms of seed size, germination rate, and parameters involving germination speed. With these variables, it was possible to group the two genotypes in a principal component analysis (PCA), where the variable most associated with Santa Fé was the relative amount of water absorbed, while for genotype 606 it was the percentage of germination. As for the morphoanatomical characteristics of the seedlings leaves, there was a difference in the morphology between the wild genotype, and the cultivated genotypes. These data show significant differences between the genotypes, facilitating the differentiation between them, and allowing choosing, within the conditions of this study, genotype 606 as the most suitable to produce quality seeds and seedlings. The in vitro micropropagation proved to be promising in relation to the decrease in germination time and seedling formation, which there was a decrease of 74 days for the formation of a seedling, for the wild genotype, and 161 days for the 606, when comparing in vivo and in vitro cultivation. Germination morphology between genotypes and propagation forms was different, since the zygotic embryos showed a more intense green color, while in the ex vitro culture, only some portions of the seeds turned green, and moreover, some explants of the wild type did not develop roots, only aerial part. Therefore, for Brazil nut trees, it is possible to use the markers related to seed biometry and germination, as well as the morphology of the leaf blade to identify the wild genotype, the cultivated genotype, and in addition, in vitro micropropagation proved to be a promising method for the production of Brazil nut seedlings in a shorter time than that used in propagation via seeds in vivo.