Duplicação do conjunto cromossômico em Coffea canephora Pierre ex A. Froehner e Coffea arabica L.

Abstract

Polyploidy refers to the occurrence of more than two chromosomal sets per nucleus. Synthetic polyploidization may be conducted in vitro under controlled physical and chemical conditions. Different polyploidization strategies may promote genomic alterations and, consequently, new individuals may exhibit different phenotypes regarding physiological, morphological and reproductive aspects when compared to their parents.However, some bottlenecks have been highlighted by different authors, such as the high explant mortality rate, low seedling regeneration rate and large number of mixoploids. In this context, cell aggregate suspensions (CAS), obtained through the indirect somatic embryogenesis (ISE) system, represent a promising plant material for in vitro chromosome doubling (CD) due to the high rate of cell proliferation. In addition, CASs are killed in constant orbital agitation, allowing more cells to have direct contact with the compounds employed for CD than in the semisolid system. In this work, we aimed to regenerate autotetraploid and auto-alloctaploid seedlings of Coffea canephora and Coffea arabica, respectively, from a new in vitro CD procedure for Coffea. Exploring the ISE, the CASs were treated with 0.0 (control), 0.5, 1.5 or 2.5 mM colchicine solution in liquid culture medium under constant orbital agitation for 48, 72 or 96 h. Inoculated in semisolid medium, SACs were renamed cellular mass (CM), which showed distinct morphogenic responses among Coffea species, treatment time and colchicine concentration. Mature cotyledonary somatic embryos were only regenerated from cellular masses treated with 2.5 mM / 48 h and 2.5 mM / 72 h treated CM for C. canephora and 0.5 mM / 48 h for C. arabica. Evaluating the DNA ploidy level, 36 (34.9%) C. canephora seedlings were classified as autotetraploid (2n = 4x = 44) and 61 (21.1%) of C. arabica as auto-alloctaploid (2n = 8x = 88).The DC procedure exploiting the CASs and ISE promoted duplication of the entire genome and resulted in a relatively high number of stable polyploids of the two Coffea species. Therefore, considering the results obtained, the methodology adopted for in vitro CD is reproducible for induction, regeneration and in vitro propagation of polyploids to Coffea and can be adapted to other shrub and woody species. Given the novelty and importance of this procedure for generating new germplasm, we show the basis and steps of the CD procedure.