14 Introgression of the corresponding S - locus region of chromosome 1 from L . esculentum into L . hirsutum and effects on reproduction Bernatzky, R . , Glaven, R . H . Department of Plant and Soil Sciences, University of Massachusetts, Amherst, MA 01003 The corresponding S - locus region of chromosome 1 from L . esculentum (cv Vendor) was introgressed into L . hirsutum (LA1777) by backcrossing to study the effects on self - incompatibility and the unilateral breeding barrier .   The initial interspecific hybrid was self - sterile (though male and female fertile), did not accept pollen from L . esculentum , but was compatible with pollen from the L . hirsutum parent .   The hybrid was backcrossed to the L . hirsutum parent and offspring were selected for the L . esculentum chromosome 1 region from RFLP markers TG125 to TG21 (approximately 8 cM) .   This region contains the self - incompatibility locus (S - locus) for the genus .   Backcrossing and selection for this chromosome region was carried out for five generations .   The selected plants remained self - sterile for all generations .   A single BC5 individual was crossed to L . esculentum (cv Vendor) to create an interspecific hybrid that was homozygous for the L . esculentum region from TG125 to TG21 .   This hybrid substitution line was self - fertile by controlled pollination and 70 seeds were collected and sown .   Sixty seedlings emerged and 45 plants were established in the greenhouse . Thirty of these plants were tested for self - fertility, compatibility with L . esculentum pollen, and for compatibility with pollen from the L . hirsutum parent .   All pollinations were done at least twice .   Pollinations were considered compatible if developing fruit had what appeared to be normally developing seeds .   Quantity and final quality of seed was not determined .   Flowers pollinated with L . esculentum pollen were emasculated; those pollinated with L . hirsutum pollen were not .   Eighteen plants did not set fruit or had fruit with poorly developed or no seed when self - pollinated .   Nineteen plants pollinated with L . esculentum pollen did not set fruit or had fruit with poorly developed or no seed .   Most plants that were self - sterile were also plants that would not accept L . esculentum pollen .   There were a few exceptions but they were not tested further .   In contrast, all plants pollinated with pollen from the L . hirsutum parent set well - developed fruit . The forty five progeny of the substituted hybrid