Abstract
Causes of low frequency in the production of triploid seeds in grapes were studied using two diploid ('Muscat of Alexandria', MA, 2x and 'July Muscat') and two tetraploid cultivars ('Kyoho' and 'Muscat of Alexandria 4x', MA 4x). The seedlings were obtained by culturing embryos from reciprocal crosses between these diploid and tetraploid culti-vars.
The formation of embryo and endosperm and the germination of the seeds obtainedfrom reciprocal crosses between diploid and tetraploid grapes were inferior to those of seeds obtained from open pollination. The inferiority was remarkably presented when dip-loid grape was used as a female plant. Hence, the development of ovules formed on 'MA, 2 x' and 'July Muscat' pollinated with 'Kyoho' and 'MA, 4x' was superior to those obtained by open pollination. However, the opposite results were obtained when 'Kyoho' and 'MA, 4x' were pollinated with 'MA, 2x' and 'July Muscat' pollens. The embryos at nine weeks after crosses of diploid × tetraploid were similar in size to those of open pol-lination, conversely embryos of the same age resulting between crosses of tetraploid × diploid were significantly smaller than those of open pollination.
The triploid embryos excised aseptically from the seeds 60 to 70 days after pollination were able to germinate on MS medium supplemented with 500 mg•liter-1 of malt extract, and they formed seedlings on the culture medium. Root-tip cells of hybrid seedlings derived from diploid × tetraploid grapes had 57 chromosomes, confirming their triploid status (n=19).
In the production of triploid grapes, the use of tetraploid grapes as a female parent seems to be superior to using diploid female parents.
