FJHST INTERNATIONAL CONFERENCE, IN EGYPT, ON PLANT TlSSUE CULTURE AND ITS APPLICATION BIOTECHNOLOGICAL STUDIES ON.INTERSPECIFIC CROSSES AMONG SOME CUCURBITA SPECIES . By Ahmed R. Aggou r , Lotfy A. Badr and Mahran M. Ashry Department of Horticulture, College of Agriculture Moshtohor, Zagazig University Benha Branch- Egypt . ABSTRACT Crosses were inade between eight different genotypes which belong to different species of genus Cucurbita. It was observed that young fruit sets . _ obtained from the interspecific crosses Green Striped Cushaw (C. argyrosperma) X Eskandaran i (C. pepo ), Butter Nut (C. maxima) X Arizona Synthetic No. l ( C.foetidissima ), Eskand arani (C. pepo ) X Arizona . Synthetic No . I (C. foetidissima ) , and Eskandaran i (C. pepo ) X Green Hubbard (C. mccd ma), began to desiccate 7 to 10 days after pollination, which cou ld be due to embryo abortion. In addition , the interspecific crosses Eskandarani (C. pepo ) X Pink Ban ana (C. maxima) and Eskandarani (C. pepo ) X Green Striped Cushaw (C. argyrosperma) gave mature fruits . However, the dry ·seeds inside these fruits contained mature embryos and rudimentary or undeveloped cotyledons. Embryo culture technique was employed to rescue such embryos . Significant differences among irnmatu re hybrid embryos of the interspecific crosses concerning weight of i1nmature embryos 30 .days after culture, and percentages of callus formation, shooting, rooting, chlorophyll formation, browning, and surviv.al were observed . The physical state of the culture medium had a significant effect on callus formed by the cultured immature hybrid embryos of the cross Eskandaran i (C. pepo ) X Green Hubbard (C. maxima). The genotype of the cultured hybrid embryos excised from the dry seeds wh ich contained mature embryos and undeveloped cotyledons, had significant effects on tl}.e different aspects of embryo culture. A successful protocol for acclimatization of plantlets resulted from culture of the interspecific hybrid embryos of the cross Eskandarani (C. pepo ) X Green Striped Cushaw (C. argyrosperma)was used. Esterase isozyme analysis using polyacrylamide gel electrophoresis indicated that the resulted banding patterns· ·were efficient in distinguish ing the plants of the interspecific F 1 hybrid Eskandarani (C. pepo ) X Green Striped Cushaw (C. argyrosperma), from the pl ants of the related parental genotypes.