2 METHODS OF HAPLOIDIZATION IN PEAR, PYRUS-COMMUNIS L - GREENHOUSE SEEDLING SELECTION AND IN-SITU PARTHENOGENESIS INDUCED BY IRRADIATED POLLEN

Seedlings of 12 crosses involving pear varieties or hybrids were obser ved for the presence of haploid plants. On the basis of phenotypic cha racteristics, 17 plants corresponded to the haploid condition and, of these, 12 were determined by chromosome counting to be haploid (2n = x = 17). In addition, and in order to induce in situ parthenogenesis, s everal pear varieties were pollinated with a selected clone carrying a homozygous dominant marker gene for the colour of red. This pollen ha d previously been irradiated with gamma-rays of cobalt 60 at 0, 200, 2 50 and 500 Grays. The immature embryos were cultured in vitro, whereby 1 haploid and two mixoploid plants were obtained. Numerous diploid pl ants with the maternal phenotype were also obtained, and their genetic origin was subsequently studied by means of isozyme analysis.