Breeding new seedless grapes using in ovulo embryo rescue and marker-assisted selection

Abstract

A program for producing new seedless table and raisin grape cultivars was initiated using embryo culture methods. F1 descendants of the cross Delight × Ruby Seedless (DRs) were used as the female parent and crossed with various seedless cultivars. The berries of DRs have excellent table traits but they retain small seed traces at maturity. Blush Seedless and DRs were used as female parents, and 354 ovules from five crosses were tested. The percentage of embryos that developed using DRs as the female parent was higher (26.7–35.8%) than when a seedless cultivar was the female parent (5.9–6.7%). The best ovule excision time [days after flowering (DAF)] for ovule inoculation was tested in another set of crosses and found to be DAF 48, 50, and 50 for DR1 × Monukka, DR6 × Thompson Seedless, and DR7 × Zhengguo Seedless, respectively. A total of 569 hybrid progeny were obtained from 13 hybrid combinations; 311 of these survived and were established in soil after hardening. We used three molecular markers (SCC8, SCF27, and GSLP1) to analyze 15 parents used in the hybrid combinations. SCC8 had a 1018-bp band in the seedless parents and in some of the DR parents, while SCF27 had a 2000-bp band in all seedless and DR parents. GSLP1 had a 569-bp band in all of the seedless parents tested, whereas the seeded and DR parents had no bands of this size. Therefore, GSLP1 was used to screen the progeny for possible seedlessness. Eight strains had the 569-bp band; these were preliminarily identified as being seedless since they are in juvenile phase, but they have not yet been evaluated for fruiting characteristics. If the strains identified by using GSLP1 are confirmed to be seedless, this marker will be a valuable tool in breeding for seedlessness in grape.