Modeling Leaf Production and Senescence in Wheat

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 leaf area development of wheat especially in high temperature environments is incomplete. The aim of this study was to quantify leaf production and senescence of 15 spring wheat cultivars. Field experiments were conducted at the research farm of the Islamic Azad University of Ramhormoz Branch, southwestern of Iran in 2006-8 using a Randomized Complete Design with four replications. The relationship between main stem leaf numbers (HS) versus degree-days was described using bilinear model. The results indicated that the leaf appearance rate therewith phylochron had no significant across all data. Mean leaf appearance rate ranged from 0.0076 to 0.0083 leaf/°C d. At thirteen of 15 cultivars, The cession time (degree-days) of effective leaf production on main stem had no significant difference and ranged from 1138.0 to 1169.3°C d. Leaf senescence on the main stem started when the main stem had about 5 leaves on main stem and proceeded at a rate of 0.0495 % per each one degree increase in degree-days. Leaf production per plant versus main stem leaf number occurred in two phases: phase 1 when plant leaf number increased with a slower (1.38 leaves per leaf) and phase 2 with a higher (4.97 leaves per leaf). A close relationship was found between the fraction of senesced leaves per plant and the same fraction on the main stem. The average leaf size on main stem was increased from 5.65 cm when there were 6 leaves on the main stem 2 and stabilized at 33.5 cm when there were 9-10 leaves on the main stem. The parameters related to leaf size had 2 no difference across all data (p<0.05). Plant leaf area was also predictable directly from main stem leaf number. The relationships found in this study can be used in simulation models of wheat.