Embriogênese somática indireta e poliploidia no gênero Coffea : base e aplicação

Abstract

Indirect somatic embryogenesis (ISE) is one of the tissue culture applications that allow the maintenance, propagation and generation of new germplasms. Thus, from the establishment of ISE in four Coffea with different ploidy levels (diploids Coffea canephora Pierre ex Froehner and Coffea eugenioides Moore; allotriploid "Híbrido de Timor" – HT, and allotetraploid Coffea arabica L.), the aims of the present study were: (a) to verify the relation between karyotype features (chromosome number, ploidy level and nuclear DNA content) and ISE; and (b) doubling the chromosome number of the allotriploid HT 'CIFC 4106'. Under the same in vitro conditions, the four Coffea varieties differed from each other during all steps of the ISE. The allopolyploids provided the highest mean number of friable embryogenic calli (FEC), in relatively short time, and visually exhibiting more pronounced cell proliferation. FEC of C. arabica resulted in the highest mean number of mature cotyledonary somatic embryos, followed by HT and C. eugenioides with the same mean value, and C. canephora with the lowest amount. Regarding the ISE data, chromosome number, ploidy level and nuclear 2C value, in vitro responses in Coffea were related to ploidy level. From established ISE, chromosome doubling of the allotriploid HT 'CIFC 4106', an anorthoploid with 2n = 3x = 33 chromosomes, was conducted by associating this in vitro system with colchicine treatment. A total of 65 plantlets were regenerated from the FEC treated with colchicine (0.5, 1.5 or 2.5 mM) for 96 h. Independently of the applied xv colchicine concentration, a rate of 49.3% of hexaploids (2n = 6x = 66 chromosomes, 2C = 4.20 pg) was obtained. In addition, the established strategy (ISE/colchicine) solved the main bottlenecks of in vitro chromosome doubling: low rate of polyploids, high number of mixoploids and high mortality. This study provided new data on the basics of ISE, understanding and contributing with a new strategy of chromosome doubling. In addition, a new Coffea germplasm, the HT 'CIFC 4106' hexaploids, was generated.