CHARACTERIZATION OF TWIN EMBRYOS IN ALMOND

Twin seeds (multiple embryos within the same seedcoat) occur spontaneously in certain almond cultivars including ‘Nonpareil’ and ‘Mission’. The occurrence of these multiple embryos varies greatly and is strongly influenced by environmental conditions. Seedlings from the same twin seed are frequently viable, though often, one of the seedlings shows weak growth and develops poorly. These dwarf seedlings are generally thought to be haploid. In this work, we characterized several seedlings from 'Nonpareil' almond twin seed, including their germination and later growth. Isozyme and Simple Sequence Repeat (SSR) markers were utilized to genetically analyze seedling genetic structure. For isozymes, AAT and PGM were analyzed using horizontal starch gel systems. For SSRs, 3 different markers were assayed using Metaphor agarose gel. In addition, individual (mitotic) karyotypes were determined from staining of root tips. Results suggest that the percentage of twin embryos showing aberrant growth was approximately 36% and that the majority of these aberrant seedlings appear to be aneuploids. The possible origin of these multiple embryos is discussed.