Root peroxidases and Rhizobium, Bradyrhizobium nodulation affinities of Phaseolus vulgaris L. and P. acutifolius A. Gray congruity backcross populations

Four parents [P. acutifolius var. acutifolius (A₁₉), P a. var. latifolius 'Serowi' (A₉), P a. var. latifolius (A₁₀), and P. vulgaris 'Red Cloud' kidney (V₁)] were used to create six interspecific recurrent and congruity backcross pedigrees (V₁ × A₉, A₉ × V₁, V₁ × A₁₀, A₁₀ × V₁, V₁ × A₁₉, A₁₉ × V₁) for evaluation of Rhizobium, Bradyrhizobium nodulation affinities and root peroxidase banding patterns. Most primary hybrids nodulated with all Rhizobium, Bradyrhizobium strains, while recurrent generations nodulated with strains of the recurrent parent, suggesting a number of independent loci and random assortment for strain-specific nodulation. A proximity matrix of nodulation phenotypes produced a cluster with V₁, two recurrent and two congruity backcross hybrids with V₁ as the cytoplasmic parent; a separate cluster with all primary interspecific and balanced, congruity backcross hybrids. A₉ and A₁₀ were clustered the farthest away from V₁. Root peroxidase zymograms of primary hybrids were the summation of the parents and controlled by independent loci. Advanced hybrids exhibited new root peroxidases, matching those found for other Phaseolus spp., including ancestral P. coccineus. A proximity matrix of root peroxidase phenotypes produced a cluster with only A₉³V₁ F₁, a cluster containing only A₁₉³V₁ F₂, and a large cluster with all P. acutifolius parents and hybrids with P acutifolius as the cytoplasmic parent in balanced hybrids or the majority parent in unbalanced hybrids. Estimation of genetic distances showed primary, interspecific hybrids to be more closely related with the cytoplasmic parent. Recurrent and congruity backcross generations varied in genetic distances between each respective parent. This is the first report of congruity backcrossing creating hybrids with biochemical traits of nonparental species.