A NEW, HIGHLY ASSERTIVE SCAR MARKER POTENTIALLY USEFUL TO ASSIST SELECTION FOR SEEDLESSNESS IN TABLE GRAPE BREEDING

Genetic changes in the genus Vitis and the domestication of vine

The genus Vitis belongs to the Vitaceae family and is divided into two subgenera: Muscadinia and Vitis, the main difference between these subgenera being the number of chromosomes. There are many hypotheses about the origin of the genus, which have been formed with archaeological studies and lately with molecular analyses. Even though there is no consensus on the place of origin, these studies have shown that grapes have been used by man since ancient times, starting later on its domestication. Most studies point to the Near East and Greece as the beginning of domestication, current research suggests it took place in parallel in different sites, but in all cases Vitis vinifera (L.) subsp. sylvestris [Vitis vinifera (L.) subsp. sylvestris (Gmelin) Hagi] seems to be the species chosen by our ancestors to give rise to the now known Vitis vinifera (L.) subsp. vinifera [=sativa (Hegi)= caucasica (Vavilov)]. Its evolution and expansion into other territories followed the formation of new empires and their expansion, and this is where the historical importance of this crop lies. In this process, plants with hermaphrodite flowers were preferentially selected, with firmer, sweeter, larger fruits of different colors, thus favoring the selection of genes associated with these traits, also resulting in a change in seed morphology. Currently, genetic improvement programs have made use of wild species for the introgression of disease resistance genes and tolerance to diverse soil and climate environments. In addition, the mapping of genes of interest, both linked to agronomic and fruit quality traits, has allowed the use of molecular markers for assisted selection. Information on the domestication process and genetic resources help to understand the gene pool available for the development of cultivars that respond to producer and consumer requirements.

New disease-resistant, seedless grapes are developed using embryo rescue and molecular markers

Improving the operation of embryo rescue technology is a highly efficient way to breed new high-quality cultivars of seedless, disease-resistant grapes when using a stenospermocarpic Vitis vinifera L. (female parents) hybrid with Chinese wild Vitis (male parents). In this study, sampling time had a significant effect on embryo recovery. Four crosses were investigated to improve the embryo rescue efficiency by determining the best sampling time, which was found to be 40, 50, 55, and 57 days after pollination (DAP) for 'Flame seedless' × 'Ruby seedless', 'Kunxiang seedless' × 'Flame seedless', 'Ruby seedless' self-pollination and 'Ruby seedless' × 'Flame seedless', respectively. The highest percentage embryo germination ranged from 60.83 to 89.10% for four cross-combinations when the embryo was germinated on woody plant medium (WPM), with 1.0-μM thidiazuron (TDZ, a potent cytokinin). For 11 cross-combinations, the embryo recovery rate varied from 4.8 to 29.6% and the plant development rate varied from 17.1 to 78.9%. 'Ruby seedless' was the best female parent followed by 'Flame seedless'. The Grape Seedless gene Probe 1 (GSLP1) and SCF27 molecular markers were used to assist the identification of the seedless traits of the 388 progeny. A total of 309 plantlets were amplified, with the specific bands at 569-bp and 2k-bp being preliminarily considered as seedless. The S382-615 marker was used to identify the downy mildew resistance of the 'Ruby seedless' × 'Beichun' cross. Two F1 progeny were amplified, with the specific band at 615-bp being identified as downy mildew resistance.

Using SCC8, SCF27 and VMC7f2 markers in grapevine breeding for seedlessness via marker assisted selection

We used molecular markers associated with seedlessness in grapes, namely SCC8, SCF27 and VMC7f2, to improve the efficiency of seedless grapevine breeding via marker assisted selection (MAS). DNA from 372 F₁ hybrid progeny from the cross between seeded "Alphonse Lavallée" and seedless "Sultani" was amplified by PCR using three markers. After digestion of SCC8 marker amplification products by restriction enzyme BgIII, 40 individuals showed homozygous SCC8+/SCC8+ alleles at the seed development inhibitor (SdI) locus. DNA from 80 of the progeny amplified with the SCF27 marker produced bands; 174 individuals had 198-bp alleles of the VMC7f2 marker associated with seedlessness. In the second year, based on MAS, 183 F₁ hybrids were designated as seedless grapevine candidates because they were positive for a minimum of one marker. Twenty individuals were selected as genetic resources for future studies on seedless grapevine breeding because they carried alleles for the three markers associated with seedlessness. The VMC7f2 SSR marker was identified as the marker most associated with seedlessness.