Observações citológicas em Coffea: XI - Métodos de tratamento pela colchicina

Colchicine treated seeds of Coffea canephora (2n = 22), C. Dewevrei (2n = 22) and C. arabica (2n=44) produced plants with doubled chromosome numbers (2n = 44 in the first two and 2n = 88 in the last mentioned species)! The strength of the solutions varied from 0,15 to 0,60% ; the treatment was given when the seeds were already germinating. The immersion of seeds in the solution even for many days did not affect the embryo. Colchicine in lanolin (0,10 to 0,60%) did not produce doubling of chromosomes when applied to buds of the same three species. A new method has been devised for the treatment of sterile plants. This is the case of the triploid (2n = 33) hybrids between Coffea arabica and C. canephora and of the di-haploid (2n = 22) form of Coffea arabica known as the monosperma variety : both are highly sterile producing only a few round seeds whose embryos are of varied chromosome numbers. The method is the following : twigs of the plants are taken to the laboratory where they are placed in individual vials containing a solution of colchicine ; after having absorbed a certain amount of the liquid, they are grafted. In the case of Coffee the strength of the solution was of 0,25 and 0,50%. Through this method, 66 - chromosome branches have been obtained on these grafts by treating original triploid (2n=33) tissue. Many 44 - chromosome branches were also obtained from a di-haploid (2n=22) variety. In the first case the sterility was almost entirely eliminated ; in the second case a complete change from sterility to fertility has occurred. This method is also applicable to other plants, when the treatment of seeds is not possible and grafting is an usual means of propagation.