Base Temperatures for Growth Processes of Lychee, a Recurrently Flushing Tree, Are Similar but Optima Differ

Abstract

Potted plants of cultivars 'Haak Yip' (Hei Ye), 'Tai So' (Da Zao) and 'Bengal' were grown in temperature-controlled glasshouse rooms at 10, 15, 20, 25, 30 or 35�C to determine cardinal temperatures for various growth processes. At other times plants of cvv. 'Brewster' (Chen Zi), 'Kwai May Pink' and 'Wai Chee' (Huai Zhi) were grown at various constant temperatures and cvv. 'Tai So' and 'Wai Chee' were grown at 27/21�C and 18/12�C (12 h day/12 h night). A modified Richards' function accurately described leaflet elongation with time. Functions fitted to derived parameters of maximum relative elongation rate and duration allowed the accurate determination of minimum and optimum cardinal temperatures for leaflet elongation. The maximum temperature for leaf elongation was well in excess of 35�C. Other processes studied included shoot elongation, increase in leaf area per plant, dry matter (DM) production, new shoot DM, DM partitioning between roots, shoots and leaves, flush periodicity, leaf morphology and total non-structural carbohydrate (TNSC) status. The minimum temperatures were similar for different processes whereas the optimum temperatures determined were different. These are compared, along with data from published studies on other physiological processes of lychee. Leaflet elongation occurred at a significantly higher optimum temperature than DM accumulation, a difference which could not be attributed to effects of temperature on partitioning, and is probably facilitated by the recurrent flushing mode of growth of lychee. There were few differences between the cultivars. 'Haak Yip' growth appeared to be more tolerant of high temperatures than 'Tai So' or 'Bengal' and 'Bengal' had higher leaf concentrations of TNSC at moderate to high temperatures. A model relating shoot periodicity to temperature (heat units) is suggested which could help in studying the relationship between flushing and flower initiation.