ブドウ‘マスカット•オブ•アレキサンドリア’の萌芽に必要な積算温度に影響を及ぼす低温の時期と程度

Abstract

The purpose of this study was to determine the accumulated chilling temperature necessary for sprouting of‘Muscat of Alexandria’(Vitis vinifera L.) grapevines. Mature grapevines in greenhouses were subjected to various cold temperatures at different times of the winter.1. When the start of heating was delayed, which prolonged the duration of natural chilling, the accumulated temperatures from the beginning of heating to budbreak, as well as those calculated from November 21, were low. The accumulated temperatures were considerably decreased when vines were subjected to low chilling temperatures during the period from late November to late December. Thereafter, however, the low temperature did not reduce the accumulated temperatures.2. The winter season from November 21 to February 28 was divided into 9 periods and the simple correlation coefficient between the mean temperature of each period and the accumulated temperature, which was summed up from the first day of each period to the day of budbreak, was calculated. The correlation coefficient was positive until early January but become negative thereafter. From November 21 to January 10, the lower temperature of each period contributed to a decrease in the accumulated temperature while after January 11, the higher temperatures caused the accumulated temperature to decrease.3. Five periods were set from November 21 to January 10, and to each period was assigned a weighted seasonal factor. The hourly temperatures were collected to make a frequency distribution with a class interval of 2.5°C. A weighted chilling factor was given to each class of temperature, and the chill unit was then calculated as follows;Chill unit=Number of hours of classified temperature×Weighted seasonal factor×Weighted chilling temperature factor.A high negative correlation coefficient (r=-0.968) was recorded between the chill unit and the accumulated temperatures for budbreak. When heating was started on any day from early December to mid April, the chill unit was highly effective for predicting the accumulated temperatures from the beginning of heating to budbreak.