Introgression in common bean x tepary bean interspecific congruity-backcross line as measured by AFLP markers

Congruity and recurrent backcross interspecific hybrids between common bean (Phaseolus vulgaris L.) and tepary bean (P. acutifolius A. Gray) were compared for the amount of introgression occurring between genomes by amplified fragment length polymorphism (AFLP) markers. A total of 60 genotypes were analyzed of which 34 were obtained by congruity backcrossing, four by single backcrossing and 14 by recurrent backcrossing, with parental and representative tepary and common bean genotypes used as controls. The level of introgression of tepary bean marker bands into the common bean genome background was higher in the congruity backcross lines than in the recurrent backcross derived genotypes. Congruity backcross lines derived from five cycles of interspecific hybridization showed an average introgression of 8.8% of AFLP bands while lines derived from a single backcross with the same parents showed an average introgression of only 5.2% of the bands. For both types of backcrossing, these levels of introgression were significantly below those expected. A multiple correspondence analysis showed three major clusters consisting of the common bean accessions and interspecifics with low rates of introgression, an intermediate group of interspecific congruity backcross lines with higher rates of introgression and a more distant group that included all the tepary bean accessions. These results suggest that congruity backcrossing can be used to increase introgression rates between the species and to transfer favorable oligogenic traits from tepary bean to common bean but that levels of introgression between the species remains low.