In Vitro Induction of Aneuploid Forms of Tetraploid Grapes by para-Fluorophynylalanine

Abstract

Mutation or somaclonal variation is one of the most useful tools in breeding of vegetatively propagated plants such as fruit trees. Mutation mainly occurs at the gene or chromosome level in a given plant. Para–fluorophenylalanine (PFP), which is an amino acid analogue, alters amino acid metabolism (Widholm, 1977), inhibits mitotic spindle formation (Thao et al., 2003) and, subsequently, reduces chromosome number to haploid number in the daughter cells (Lhoas, 1961). The effect of PFP on the reduction of chromosome number has been firstly reported in diploid Aspergillus niger from which haploid cells were induced (Lhoas, 1961). After this report, similar effects of PFP have been described in many plants such as Ribes (Knight et al., 1963), Allium (Sinha and Bhojwani, 1976), Fragaria (Niizeki and Fukui, 1983) and Alocasia (Thao et al., 2003). In Vitis, it has been reported that PFP effected on the change of chromosome number in the root cells of seedlings (Omura and Akihama, 1980; Omura et al., 1985) and induction of a triploid from PFP–treated shoots of tetraploid ‘Kyoho’ (Omura and Akihama, 1981). However, there are no reports as to somaclonal induction of hyper– and hypo–tetraploid grapes by PFP treatment. Hyper– and hypo–tetraploid grapes (2n=4x±1 or 4x±2) resulting from failure or irregularity of meiosis were found as a spontaneous (probably S1) seedling of ‘Kyoho’ (Yamane et al., 1978), appeared in selfed seedlings with abnormal cotyledons in ‘Kyoho’ (Park et al., 1999a) and rarely found in hybrid seedlings from interploid crosses between triploid and tetraploid grapes (Park et al., 1999b, 2002). ‘Takao’, a spontaneous hypotetraploid seedling of ‘Kyoho’, produces almost seedless berries of small size, but it produces large seedless berries with the aid of gibberellin treated at full bloom (Ashikawa, 1972). Thus, the crossing between tetraploid cultivars, followed by selection of the resultant seedlings with abnormal cotyledons, is an excellent method to obtain hyper– and hypo–tetraploid hybrid grapes for breeding of seedless cultivars. On the other hand, direct induction of hyper– and hypo–tetraploid forms from excellent but seeded tetraploid grape cultivars without crossings may be useful for establishing seedlessness in the seeded cultivars without greatly loosing their high tree vigor and other characters such as productivity, large berry size (Reisch and Pratt, 1996; Notsuka et al., 2000) and berry quality, although high parthenocarpy is required for the original cultivars to set and produce large–sized seedless berries without gibberellin treatment. To establish the efficient method to produce hyper– and hypo–tetraploid forms, we studied the effect of in vitro PFP treatment on the small change in tetraploid chromosome number in cultured shoots of ‘Kyoho’, colchiploid of ‘Rozaki’ and ‘Kyoho’ hybrids, all of which are tetraploid plants with relatively high parthenocarpic ability.