Abstract

In order to work out an effective haploidization method in lettuce (Lactuca sativa), we attempted to induce the development of haploid embryos by chemical treatment of pistils or through wide crossing of lettuce with 25 species (mostly of the Asteraceae family). The highest frequency of embryos was achieved after crosses withHelianthus annuus (16%) or H. tuberosum (19%). All the embryos, developed up to the globular or heart stage, were haploid (n = 9). Stigma treatment with seven of the eight tested chemical inductors resulted in the development of only several celled embryos, of which the most effective were: 0.05% Dicamba (15%), 0.05% Picloram (14%), and 0.05% 2, 4-D (13%). Embryo haploidy was verified by: counting of chromosomes in dividing cells and comparison of nucleus perimeter. The processes of pollination and embryogenesis were analysed under light and fluorescence microscopes.

Key words: Intergeneric crossing, lettuce, parthenogenesis, chemical induction, haploidization.