Effect of Root Temperatures under Forced Conditions on Budbreak, Shoot Growth, and Development of Flower Cluster of ‘Muscat of Alexandria’ Vines

Abstract

Investigations were carried out in order to clarify the effect of root temperature conditions on budbreak, shoot growth, and the development of flower clusters of ‘Muscat of Alexandria’ vines. Root temperatures were controlled under forced conditions. One year old potted non-fruiting vines, 2 to 3 years old potted fruiting ones, and 5 years old benched fruiting vines were used. All the vines were on the H. F. rootstock.
In the plots where heating was started in December and in February, the amount of sap bled through the cane was larger at 27°C than at 13°C, especially just after the start of forcing, when the amount of sap in the 27°C treated plants was twice that in 13°C treated ones.
The number of new roots which were measured at the sprouting date of the 27°C plot was very large in vines treated at 20 and 27°C, and quite large in vines treated at 34°C. Rooting at 13°C was scarcely observed throughout the experiment.
When vines were forced from January, higher root temperatures resulted in fewer days being required for budbreak. The percentage of budbreak was also higher in the plots at 25 and 30°C than in those below 15°C. When forced from December, the budbreak percentage increased and also the number of days required for budbreak was reduced. In vines forced from February and from March there were no differences among the treatments.
The shoot growth of potted vines was more vigorous at 20 and 27°C than at 13°C. However, in the case of benched vines the difference in shoot growth between the plots at 13 and 27°C was small. These results were obtained for all durations of heating. In the potted vines heated from both December and February, the number of flower clusters per shoot and the cluster development were greater at 27°C than at 13°C. In the benched vines, forcing from December resulted in more vigorous development of flower clusters at 27°C than at 13°C. Only slight differences between the plots were observed when vines were forced from February.
Although the temperature control of roots was terminated three weeks after blooming, the berry size at harvest was larger in vines treated at 27°C than at 13°C for all durations of heating.