Flushing and Leaf Growth of Cacao Under Controlled Temperature Conditions

Abstract

Young clonal cacao trees have been grown for nine months in controlled- environment rooms at 74° F.,80°F. or 86° F. (23·3° C., 26·7° C., or 30·0° C.), or at one of these temperatures during the day and another during the night. No specific temperature requirements for leaf flushing, which occurred in all the treatments, were found. Flushing was considerably greater at the higher temperatures, partly as a result of the loss of apical dominance, and was especially sensitive to day temperature. The number of expanded leaves per flush and mean area per leaf increased with a decrease in day or night temperature, as did the duration of the leaves on the trees. The biggest net leaf area increases were made by plants given a day at 80° F. and a night at either 80° F. or 74° F. A night temperature of 86° F. resulted in a rapid turn-over of small unhealthy leaves having a low chlorophyll content. The gain in total plant dry weight was greatest at a night temperature of 74° F., smallest at a night temperature of 86° F., and the plants which maintained the greatest leaf areas also gained the most dry weight. Leaf dry weight per unit leaf area was greatest at the lowest temperatures, as was the ratio of total plant dry weight to leaf area. The ratio of leaf weight to plant weight showed a small but significant increase with increase in day temperature.