Development of molecular markers linked to the stenospermocarpic seedlessness of grapvines

Seedlessness is basic requirement in table grape breeding. In a breeding program with multiple resistance genes combined with seedlessness, the number of appropriate combinations is very low. As such, the availability of early selection is crucial. Marker assisted selection (MAS) offers an efficient tool for genotyping stenospermocarpic seedlessness in grapevines. During the last 15 years, several markers were developed for the selection of seedlessness of grapes, from which the cleaved amplified polymorphic sequence SCC8 and the simple sequence repeat p3_VvAGL11 are the two best characterized. Although these markers have been tested on a wide range of seeded and seedless genotypes, the involvement of different disease resistance sources initiated the review of the general applicability of these markers.

Several seeded and seedless varieties with diverse geographical origin, further families with different genetic background for fungal disease resistance (complex hybrids of Vitis vinifera and North-American Vitis species, Muscadinia rotundifolia back cross, V. vinifera 'Kishmish vatkana') were tested with SCC8 and p3_VvAGL11 markers. The investigated genotypes are involved in a breeding program of the Institute of Viticulture and Oenology at the University of Pécs, where seedless grapes with immunity grade resistance against powdery and downy mildew, suitable for organic vine growing are bred.

In the case of SCC8, the high frequency of the SCC8 null allele (which is linked to seededness) and the relatively high number recombinants among seeded resistance sources makes the applicability of the marker limited. p3_VvAGL11 is proposed to be an in-promoter marker of seedlessness located in the very close vicinity of VvAGL11, which is in turn supposed to be the best candidate for the seed development inhibitor gene (SdI), the main genetic determinant of seedlessness. This marker does not suffer from the drawback of null alleles. Seeded varieties however, which are recombinant between SCC8 and SdI (V. vinifera 'Katta kurgan', 'Dshandshal kara'; Muscadinia rotundifolia hybrids), were also recombinant between p3_VvAGL11 and SdI.

Stenospermocarpic seedlessness is a complex trait, where seed development also depends on several minor effect genes. As a consequence, MAS based on SdI is prone to be less reliable by nature. Based on our results, the applicability of available markers for MAS of grapevine seedlessness is even more limited, if modern fungal resistance sources are applied.