Abstract:
Interspecific hybridization between Phaseolus vulgaris and P.
coccineus results in the formation of either mature F₁ seeds or abnormal
embryos, depending on the direction of the cross. However, normal as
well as abnormal embryos occur in the reciprocal F₂ populations. The
exact cause of abnormal embryo development is unknown. To determine if
there is a correlation between the genomic composition and embryo
development (normal vs. abnormal), isozyme banding patterns were
examined in the reciprocal F₁ and F₂ progenies of P. vulgaris cv. Great
Northern (GN) and P. coccineus cv. Scarlet Runner (SR). Three enzyme
systems, acid phosphatase (AP), esterase (EST), and malate dehydrogenase
(MDH) were analysed in extracts of immature embryos at the cotyledonary
stage. Parental species and reciprocal F₁ and F₂ embryos exhibited
clear differences in electrophoretic patterns. The embryos of
reciprocal crosses displayed banding patterns characteristic for their
developmental type (normal or abnormal). AP and MDH zymograms of normal
embryos were closer to those of the GN parent, whereas abnormal embryos
had isozyme bands similar to those of SR. Differences in EST banding
patterns were apparent between normal and abnormal F₂ embryos, however,
these patterns did not resemble either parent. The results indicate
that embryo development can be correlated with particular isozyme
patterns which may at least in part reflect the genetic combination.
They also seem to substantiate the hypothesis that the skewed
distributions of quantitative traits in interspecific progeny
populations could be related to selective survival of seeds containing
normal embryos.
