Introgression into the allotetraploid coffee (Coffea arabica L.): segregation and recombination of the C. canephora genome in the tetraploid interspecific hybrid (C. arabicaxC. canephora)

Transfer of desired characters from the diploid relative species such as Coffea canephora into the cultivated allotetraploid coffee species (Coffea arabica L.) is essential to the continued improvement of varieties. Behaviour of the C. canephora genome and its interaction with the C. arabica genome were investigated in tetraploid interspecific hybrids (C. arabica x C. canephora 4x) resulting from a cross between an accession of C. arabica and a tetraploid plant of C. canephora obtained following colchicine treatment. Segregation and co-segregation of restriction fragment length polymorphism (RFLP) and microsatellite loci-markers were studied in two BC1 populations. These two populations of 28 and 45 individuals, respectively, resulted from the backcross of two tetraploid F1 plants to C. arabica. The presence in BC1 plants of specific C. canephora markers was scored for 24 loci (11 RFLP and 13 microsatellites) distributed on at least 7 of the 11 linkage groups identified in C. canephora. At almost all loci analysed, the segregation of C. canephora alleles transmitted by the (C. arabica x C. canephora 4x) hybrids conformed to the expected ratio assuming random chromosome segregation and the absence of selection. The recombination fractions of C. canephora chromosome segments were estimated for seven marker intervals, and compared with the recombination fractions previously observed in C. canephora for the equivalent marker intervals. The recombination frequencies estimated in both plant materials were rather similar, suggesting that recombination in the (C. arabica x C. canephora 4x) hybrid is not significantly restricted by the genetic differentiation between chromosomes belonging to the different genomes. The hybrid (C. arabica x C. canephora 4x) therefore appeared particularly favourable to intergenomic recombination events and gene introgressions.