Effects of exogenous application of plant growth regulators on the development of ovule and subsequent embryo rescue of stenospermic grape (Vitis vinifera L.)

Seedless grapevine cultivars (Vitis vinifera L.) are widely grown in Europe, America and Asia. Abortion of zygotic embryos in seedless grapes largely limits the efficiency of breeding of seedless cultivars through genetic crossing. The present study was designed to investigate effects of exogenously applied plant growth regulators (PGRs) to the grapevines in field condition on ovule and subsequent embryo rescue of seedless grapes of small seed traces. First experiment was performed by measuring ovules weight, proportion of each category ovules in maturity and embryo development in vitro of seedless grape cv. Centennial Seedless, Thompson Seedless and Crimson Seedless sprayed by chlormequat (CCC), benzyladenine (BA), ethephon (CEPA) and putrescine (Put). The effects of different application concentration and date of CCC were further evaluated in Centennial Seedless in later experiment. The results showed that exogenous application of all PGRs did not affect the total number of ovules per berries in maturity. CCC increased the ovules weight and proportion of ovules >4 mm in length of three varieties in maturity. The effects of two application times of PGRs on weight of berries and ovules and proportion of each category ovules in maturity were not significantly different. In the proceeding of embryo rescue, CCC at 100 and 1000 mg l⁻¹, BA at 100 mg l⁻¹ and Put at 20 mg l⁻¹ increased the percentage of developed embryos of Centennial Seedless and Thompson Seedless. The results showed that the size of ovules excised for embryo rescue significantly affected embryo formation and plant regeneration. The percentage of embryos formation in ovules >4 mm in length was significantly more than in ovules 2–4 mm in length, no embryo was found in ovules <2 mm in length. Exogenous application of CCC at 100–500 mg l⁻¹ significantly increased percentage of ovules >2 mm in length by 80.0–82.7% in Centennial Seedless, therefore improving embryo formation. The statistical correlation was found between the proportion of ovules >2 mm and embryo formation (r = 0.92) in Centennial Seedless. Among the different spraying time in Centennial Seedless, CCC applied 14 days before bloom produced significantly more ovules >2 mm in length and embryos formation.