Origin of polyembryonic seeds and production of haploids in asparagus

The population of asparagus has high heterogeneity because of its dioecious nature, and it is difficult and time consuming to produce inbred lines. Production of doubled haploid lines is actually commonly used by plant breeders in order to obtain pure lines in the shortest possible time. In this study, production of haploid plants was attempted by means of polyembryonic seeds, and origin of polyembyonic seeds was also investigated through simple sequence repeat (SSR) and flow cytometric analyses. Seeds obtained from 18 combinations of crosses were provided. The frequency of seed germination was 92.9% (2,718 seeds germinated out of 2,925 seeds sown). Twenty polyembryonic seeds were obtained with the frequency of 0.7% (20 polyembryonic seeds out of 2,718 seeds germinated). All polyembryonic seeds had two seedlings. Survived 20 seedlings from ten polyembryonic seeds were used for investigation of ploidy levels and SSR analysis. Out of 20 seedlings three were haploids (2n=2x=10), one triploid (2n=3x=30) and 16 were diploids (2n=2x=20). SSR analysis proved that occurrence mechanism of polyembryonic seeds was various, and it was classified into types 1 to 10 in the current study. Four types of the mechanism of the occurrence of polyembryonic seeds were suggested in the case that twin seedlings were both diploids. Two and one types of the mechanism were indicated in the cases of the combinations of diploid and triploid and of diploid and haploid, respectively. Three types were estimated for the occurrence of polyembryonic seed that both seedlings showed haploids.