TOMATO BREEDING .1. EMBRYO RESCUE OF INTERSPECIFIC HYBRIDS BETWEEN LYCOPERSICON-ESCULENTUM MILL AND LYCOPERSICON-PERUVIANUM (L) MILL

Some introductions of Lycopersicon peruvianum represent promising sour ces of resistance to tomato spotted wilt virus (TSWV) however, a high level of incompatibility has been found between these introductions an d L. esculentum which limits their utilization in tomato breeding prog rams. Culturing of immature hybrid embryos with subsequent shoot forma tion from calli developed from embryogenic cells, permitted the recove ry of F1 interspecific hybrids. Histological analysis of hybrid embryo development demonstrated that at 25 days after pollination nearly all embryos had aborted. Therefore, immature embryos 15-25 days old were used for in vitro culture. Attempts were made to obtain hybrid tomato plants through embryo rescue in interspecific crossings. Culture media with variable concentrations of auxins and cytokinins and with the ad dition of complex additives were tested. The best treatment was the ad dition of 10 muM 6-BA and 2.5 mu IAA, which gave rise to callus format ion in about 20% of the immature embryos. Four callus lines were isola ted which gave normal shoot formation. Rooted plantlets were gradually adapted to greenhouse conditions and a total of 128 hybrid plants wer e transplanted to a field nursery. The hybrid nature of the regenerate d plants was demonstrated by morphological characters, including leaf and fruit color and shape, exerted stigma and hairiness. Isozyme analy sis for acid phosphatase ad phosphoglucoisomerase confirmed the hybrid nature of F1 plants.