Effects of Root Temperature under Forcing Conditions on Carbohydrate Contents of ‘Muscat of Alexandria’ Vines

Abstract

Investigations were carried out to clarify the effects of root temperature on carbohydrate contents in potted or benched ‘Muscat of Alexandria’ vines grafted on ‘Hybrid Franc’ rootstock. Root temperature was controlled to 13°C and 27°C from December nd from February, under forcing conditions. Seasonal changes in carbohydrate contents in unheated vines were also determined for comparison.
1. In vines heated from both December and February, the higher the root temperature, the fewer days to budbreak, the higher the budbreak percentage, and the more vigorous the shoot growth, especially in forcing from December. When forced from December, development of flower clusters was more vigorous at 27°C than at 13°C, while there was little difference between the two temperatures from February forcing.
2. In unheated vines, starch content decreased toward bursting stage in all parts, including rootlets (below 2mm in diameter), lateral roots, trunk and cane, especially in the rootlets. However, total sugar content in each part increased up to Junuary or February; after reaching a maximum level, it decreased rapidly toward bursting, especially in canes. When forced from December, total sugar content in canes increased after the start of the treatments at both 13°C and 27°C, and decreased toward bursting, especially at 27°C, where budbreak was promoted. On the other hand, there was a marked decline just after the start of the treatments on total sugar content at either temperature forced from February. Starch content in rootlets decreased markedly toward bursting at 27°C with forcing from both December and February, whereas no notable difference between the two temperatures was observed in canes. The pattern of seasonal changes in trunk and lateral roots corresponded to that in canes and rootlets, respectively.
3. The lowest concentration of total sugar in sap bled from canes was observed at bursting stage in unheated vines, whereas in heated vines it occurred just after the start of the treatments in all plots. Sugar concentration in sap was always lower at 27°C than at 13°C, regardless of time of forcing. When heated from December, content of starch and sugars in shoots was less at 27°C, at which growth of shoots and clusters was vigorous, than at 13°C, but little difference was found between the two temperatures from February.
4. From these results, it was considered that the poor growth of shoots and clusters which occurred at the low root temperature of 13°C in vines heated from December, due to the fact that the seasonal change in carbohydrate nutrients in vines was small throughout the short growing period, and that the utilization of carbohydrates in shoots was also small.