Heterozygosity level and its relationship with genetic variability mechanisms in beans

Resumo

Heterozygosity is an extremely important resource in early breeding programs using autogamous plants because
it is usually associated with the presence of genetic variability. Induced mutation and artificial hybridization can increase
distinctly the proportion of loci in heterozygosis. This study aimed to compare segregating and mutant populations and relate the
mechanisms used to generate variability with their respective heterozygosity levels tested. The treatments mutant populations
(M2
, M3
, M4
, M5
, M6
and M7
), segregating populations (F4
, F5
and F6
) and lines (BRS Pérola and IPR Uirapuru) were evaluated
by multivariate analysis and compared by orthogonal contrasts. The canonical discriminant analysis revealed which response
variables contributed to differentiate the treatments assessed. All orthogonal contrasts involving the mutant populations showed
significant differences, except the contrast between M2
vs. M3
, M4
, M5
, M6
, M7
. The orthogonal contrast between the mutant and
segregating populations denotes a significant variation in the interest in genetic breeding. The traits stem diameter (1.41) and
number of legumes per plant (2.72) showed the highest canonical weight in this contrast. Conversely, number of grains per plant
(-3.58) approached the mutant and segregating populations. No significant difference was observed in the linear comparison of
means F5
vs. F6
. The traits are fixed early in the segregant populations, unlike the mutant populations. Comparatively, induced
mutation provides more loci in heterozygosis than artificial hybridization. Selection pressure should vary according to the
variability creation mechanism used at the beginning of the breeding program.