Degree of abortion and germination rates in triploid seeds from crosses between diploid and tetraploid grapes (Vitis vinifera L. and V. complex)

Interploid crosses were carried out using seven diploid and four tetraploid grape cultivars to examine the degree of triploid seed development. The average number of seeds per pollinated flower was 0.42 for 2x×4x, 0.51 for 4x×2x, 0.78 for 4x×4x and 1.21 for 2x×2x crosses. About 47% of seeds from the 2x×4x crosses and 44% of seeds from the 4x×2x crosses were sinkers. Nineteen of 1012 seeds from the 2x×4x crosses and 32 of 1170 seeds from the 4x×2x crosses germinated. Among these crosses, 'Yufu'×'Sekirei' and its reciprocal cross exhibited the highest (4.4%) and next highest (3.6%) rates of seedling production per flower. All of the seedlings examined were triploid (2n=3x=57). In comparison with diploid and tetraplid seeds from the intraploid crosses, reduction of seed size was prominent in seeds from the 4x×2x crosses but not in seeds from the 2x×4x crosses. About 10% to 30% of seeds from the interploid crosses had fully developed endosperm and 80% of seeds with the fully developed endosperm contained embryos at globular to torpedo stages. The rate of seeds with embryo was higher in the 4x×2x crosses than the 2x×4x crosses. However, difference in embryo and endosperm development was not detected between the 2x×4x and 4x×2x crosses. These results suggested that in the interploid crosses endosperm block is partial or flexible and that germination rates of the triploid seeds are very low but different in different crosses.