Fertilização in vitro: uma estratégia para o melhoramento genético da bananeira

Abstract

Banana is one of the most important fruit crops in Brazil. Although Prata type cultivars are the mainly produced and commercialized cultivars in the internal market, the cultivars from the Cavendish subgroup are the most accepted in the international market. The Nanica, Ninicão and Grande Naine cultivars of the Cavendish subgroup are susceptible to black-Sigatoka. One of the great limitations of genetic breeding of Cavendish is the difficulty in the obtainment of seeds in crosses, due to physical and/or biochemical barriers that occur during the fertilization process. The objective of the present study was to develop an in vitro methodology of fertilization for the obtainment of banana hybrids from the Cavendish subgroup. The in vitro germination and the viability of pollen grains of diploid (AA) hybrids improved through the banana genetic breeding program at Embrapa Cassava and Tropical Fruits, were initially evaluated. The germination percentage varied from 2.98 to 90% and the growth of the pollen tube from 0.67 to 4.25 mm, when cultivated in medium with pH 7.0. Most genotypes presented pollen viability above 90%. The genotypes with greater percentage of germination and longer pollen length were used in the in vitro and in vivo fertilization experiments. Daily pollinations were carried out in twenty diploid and twenty triploid plants and in both ploidy levels the development of the ovules were evaluated through comparisons. It was observed that in the diploids the ovules increased in volume starting from the second day after pollination, whereas for the triploid cultivars, a smaller reduction in size was observed. Many in vitro fertilization methodologies were evaluated but the effective occurrence of the process was not verified.