The effect of temperature on leaf emergence rates of sunflower genotypes

Abstract

A major component in a crop growth model is leaf area development, which has a major influence on photosynthesis and transpiration. The knowledge about the response of sunflower ( Helianthus annuus L.) development to temperature is incomplete, especially the effects of unusually low and high temperatures. A series of experiments was conducted to quantify the relationships between temperature and development of leaf area in four sunflower hybrids. Plants were grown in the greenhouse until six leaves had appeared and then taken to growth chambers, where rates of leaf appearance were measured under nine temperature regimes that ranged from constant 34°C to 12/5°C (10/14 h). Leaf appearance rate increased with temperature up to 27°C. Combining the data from all the hybrids, the base temperature for leaf appearance was 4°C, which is below previous reported values. Thermal time in degree-days (°Cd) per leaf was between 20 and 25. Contrasting results were obtained in a second experiment where temperature treatments started from sowing and were changed when the sixth leaf appeared. The discrepancies suggest that temperature soon after emergence will affect the subsequent rate of leaf appearance. The relation obtained under controlled conditions was in agreement with data from field experiments at several locations. The information presented will be useful in modelling the appearance of leaves of sunflower in response to environmental conditions.