USE OF THE MULTI-ALLELIC SELF-INCOMPATIBILITY GENE IN APPLE TO ASSESSHOMOZYGOCITY IN SHOOTS OBTAINED THROUGH HAPLOID INDUCTION

To obtain homozygous genotypes of apple, we have induced haploid devel opment of either the female or the male gametes by parthenogenesis in situ and anther culture, respectively. Of the shoots obtained, which w ere mainly of a non-haploid nature, some could be derived from fertili sed egg cells or from sporophytic anther tissue. In order to select th e shoots having a true haploid origin, and thus homozygotes, we decide d to use the single multi-allelic self-incompatibility gene as a molec ular marker to discriminate homozygous from heterozygous individuals. The rationale behind this approach was that diploid apple cultivars co ntain 2 different alleles of the S-gene and therefore the haploid indu ced shoots obtained from them should have only one of the alleles of t he single parent. The parental cultivars used were 'Idared' (parthenog enesis in situ) and 'Braeburn' (androgenesis), and their S-genotypes w ere known, except for 1 of the 'Braeburn' S-alleles. To stimulate part henogenetic development 'Idared' styles were pollinated with irradiate d 'Baskatong' pollen, the S-alleles of the latter (2n) cultivar were a lso unknown. The cloning and sequence analysis of these 3 unidentified S-alleles, 1 from 'Braeburn' and 2 from 'Baskatong' is described, and we show that they correspond to the S-24-, S-26- and S-27- alleles. W e have optimised a method for analysis of the S-alleles of 'Idared/Bas katong'- or 'Braeburn'-derived in vitro plant tissues and have shown t hat this approach can be applied for the screening of the in vitro sho ots for their haploid origin.