2017 ASHS Annual Conference

Seedlessness is one of the most important traits of table grapes, as consumer demand for seedless grapes has increased yearly in the global market. Thus, many grape breeders have strived to develop seedless varieties. Economic usefulness of aneuploid plants is rarely evaluated because aneuploid plants often exhibit developmental abnormalities, sterility, or lethality. Male or female sterility in grapes, however, can provide the opportunity to induce seedless fruits via a one-time application of a plant growth regulator during the full blooming period. Since polyploid plants generally have larger fruit, better disease resistance, and greater adaptability than diploid plants, fostering hypo- or hyper-tetraploid (2n=4x±1 or 4x±2) hybrids is an effective way to develop new seedless grape varieties with highly desirable traits. In Vitis, a small number of hypo- or hyper-tetraploid seedlings were reported to result from para-fluorophenylalanine treatment and cross-pollination of tetraploid grape cultivars. Therefore, the low occurrence of hypo- and hyper-tetraploid seedlings is the main barrier to developing new hypo- or hyper-tetraploid grape varieties. In this study, we investigated the chromosome numbers in the progenies of hypo- and hyper-tetraploid grapes obtained from open-, self-, and cross-pollination to evaluate whether this technique could be applied to develop new seedless grape cultivars. Three of the five seedlings (60%) from ‘Takao’ were aneuploid, including one with 74 chromosomes (2n=4x-2) and two with 75 chromosomes (2n=4x-1). In ‘RB9127K’, 26 of the 193 seedlings (13.5%) were aneuploid, including three seedlings with 75 chromosomes (2n=4x-1), 18 with 77 chromosomes (2n=4x+1), and five with 78 chromosomes (2n=4x+2). The high frequency of aneuploids from ‘Takao’ and ‘RB9127K’ grape indicates that meiosis in hypo- and hyper-tetraploid female parents is prone to segregation error. These results suggest that various hypo- or hyper-tetraploid seedlings can be successfully produced using hypo- or hyper-tetraploid grapes as female parents, which can contribute to the development of new seedless grape varieties with large berries.