The influence of site environment and the effects of varying light and temperature on inflorescence development and flowering in grapevines, Vitis vinifera L. Cabernet Sauvignon

Abstract

Seven vineyards representing three viticultural regions from throughout New Zealand were selected to investigate the influence of site environment on cropping potential, inflorescence development and fruit set of grapevines (Vitis vinifera L. Cabernet Sauvignon). The number and size of inflorescence primordia at bud positions 2-6 from the base of randomly selected canes were determined by dormant bud dissection. Differences between sites were assessed in relation to heat accumulation, bud size and the growth of miniature grapevines from cuttings collected at each site. Site had a significant effect on many of the factors being assessed. Warmer sites are expected to have larger buds, greater numbers of inflorescence primordia within the buds and, in general, to exhibit larger inflorescences with enhanced success of pollination and fertilisation at flowering, resulting in increased yields.

In a second series of experiments the effects of modifying the light and temperature environment of developing shoots and inflorescences, as well as that of well developed inflorescences was investigated in two field trials established at Lincoln University. Light and temperature were shown to have a combined effect on early shoot growth and inflorescence development, probably as a consequence of differences in the photosynthetic activity of the developing leaves. The same treatments had few significant effects on the futher development of inflorescences treated 20 days preanthesis to 5-7 days post anthesis. Fruit set in treated inflorescences was reduced by excessively high or cool temperatures. It is suggested that a combination of high light intensity and warm temperature has its greatest effect on the development of the grape inflorescence, in the two weeks following bud break.

During the course of this study an investigation into the concept of ‘fitness to flower’ was explored. It was proposed that the limiting factor for inflorescence development and increased fruit set was the size of the peduncle and associated vascular tissues. Evidence is presented which suggests that the grapevine controls flowering by regulating the allocation of available carbohydrates to the developing inflorescence.