A Modified Method for Inducing Precocious Flowering in Grape Seedlings

Abstract

Breeders of woody perennials seek to shorten the time from propagation to flowering and the turnover time between generations. Grapevines usually flower and fruit no earlier than their third season. Onset of flowering occurs when anlagen, undifferentiated primordia arising from axillary and terminal bud meristems, begin to develop into inflorescences as well as tendrils. This occurs in response to hormonal stimuli; high levels of gibberellins in juvenile tissue favor vegetative growth, whereas increased cytokinin levels in physiologically mature tissue favor reproductive growth. We modified a method developed for Vitis vinifera for use on grape rootstock seedlings. Exogenous applications of chlormequat and N-benzyl-9-(2-tetrahydropyranyl) adenine (PBA, a cytokinin) were used induce precocious flowering by increasing the cytokinin:gibberellin ratio, triggering anlagen to develop into inflorescences on physiologically juvenile vines. The optimum treatment was a single application of 3000 micromolar chlormequat and 250 micromolar PBA, followed by 10 subsequent daily applications of PBA alone. Lower concentrations of treatments resulted in a loss of efficacy, and higher treatment concentrations and/or longer durations resulted in phytotoxicity. Abnormalities in flower and leaf morphology were observed with all treatments. Grape rootstock seedlings are dioecious and staminate vines were more responsive to the treatments than pistillate vines. We did not observe production of hermaphroditic flowers on staminate vines. Pollen collected from flowering staminate seedlings was successfully used in crosses that produced fruit and viable seeds. The ability to induce precocious flowering in juvenile grape seedlings has many applications in grape breeding and genetic research.