Utilização de recursos genéticos do gênero Manihot no pré-melhoramento genético de mandioca

Abstract

The cassava (Manihot esculenta Crantz) native to the American continent is used in the human and animal feeding or as raw material for several industries. Actions directed to the pre-improvement are relevant in order to subsidize the obtainment of hybrids with superior characteristics. The objective of this work was to characterize the production, the size and the viability of pollen grains of accessions of different species of the genus Manihot, as well as to evaluate procedures to preserve pollen grains of wild cassava. The estimate of the pollen production was accomplished by the number of pollen grains produced per flower bud and the diameter was determined by the transversal length of the grain. The viability of the pollen was evaluated by ‘in vitro’, ‘in vivo’ and colorimetric tests. The average production observed among all the accessions was 1.253 pollen grains. The highest production was observed in the accession DIC 587-05, with a mean production of 3.638 pollen grains/flower, while the lowest was in the accession FLA-029-01 with a mean production of 579 grains. Regarding the size of the pollen grain, it was verified that in the wild accessions the size ranged from 132 to 163 Ym and from 129 to 146 Ym in the cultivated ones. The viability of the pollen grains was high through the colorimetric tests, medium in the ‘in vivo’ tests and there was no germination in the culture medium. Studies of the pollen ultrastructure were accomplished by sweeping electronic microscopy evidencing structural differences among the wild species. Pollen of the wild accession FLA- 005-07 was stored in four different temperatures (27ºC, 4ºC, -20ºC, -80ºC) and for two different periods (three months and six months). The stored pollen grains of the wild accessions suffered significant losses of viability, being necessary new studies on that subject.