1975 Volume 43 Issue 4 Pages 387-392
The combination effects of day-length and temperature on the growth and bunch differentiation of grapes were observed with one-year-old grafted vines of Delaware (V. labruscana) and Muscat of Alexandria (V. vinifera) in natural light growth cabinets by treating as follows; i) 20°C-short day (8-hour), ii) 20°C-long day (16-hour), iii) 30°C-short day (8-hour), and iv) 30°C-long day (16-hour).
1) In Delaware, shoot growth and bunch differentiation were greatly retarded on short days regardless of temperature, while promoted remarkably on long days, the trend being more marked at 20°C than at 20°C. However, shoots elongated so rapidly on 30°C-long days that most of lateral buds at their basal part became barren.
2) In Muscat of Alexandria, shoot growth and bunch differentiation were less sensitive to day-length than to temperature. Shoot growth was considerably ensured at 30°C even on short days, though it was greatly retarded on 20°C-short days. Bunch differentiation was best on 30°C-long days, followed by 30°C-short days, 20°C -short days, and 20°C-long days in the order. Particularly no bunch differentiation occurred on 20°C-long days all along the shoot.
3) Therefore, to utilize fully the room space in the vine growing under glass or plastic film, 20°C-long days seem to be best condition for Delaware, and 30°C-long days for Muscat of Alexandria from the stand-points of shoot growth and bunch differentiation. It is, however, noticeable that root growth and wood maturity were generally better on short days than on long days in both cultivars.