Embryogenèse précoce comparative lors des croisements entre Phaseolus coccineus L. et Phaseolus vulgaris L.

Comparative early embryogenesis in crossings between Phaseolus coccineus L. and Phaseolus vulgaris L. Theinterspecifi c hybridization between Phaseolus coccineus L. and Phaseolus vulgaris L. is useful for the genetic improvementof the common bean. The use of the P. vulgaris cytoplasm for such hybridizations leads usually to a rather fast return tothe maternal form in the subsequent generations. When P. vulgaris is the pollinator, crosses result in early embryo abortion(globular or heart-shaped embryos). A competition between the endosperm and the embryo, on the one hand, and between thesuspensor and the embryo, on the other hand, could generate diffi culties of feeding young embryos. Histological sections usingthe 2-Hydroxyethyl Methacrylate (HEMA) resin method on the embryos of P. coccineus (NI16) and P. vulgaris (NI637 andX707) genotypes, as well as on their genotypic combination (NI16 × NI637 and NI16 × X707 and reciprocal crosses) enableus to explain partially these abortion cases. Observations concern embryos from 3 to 6 days after pollination (DAP). Embryodevelopment (suspensor and embryo proper) of the hybrids is slower than that of the parents whatever the crossing. Ingrowthsof suspensor basal cells observed when P. coccineus is the maternal parent are characteristic of the presence of the cytoplasmof these species. Endothelium deterioration (or proliferation) in hybrid embryos would rather be related to the degree reachedby the process of abortion in the embryo concerned