Quantifying Leaf Development in Different Wheat Cultivars: Leaf Lifetime

A major component in a crop growth model is leaf area development, which has crucial influence on photosynthesis and transpiration. Leaf area development involves the appearance of new leaves, expansion of the newly emerged leaves and senescence of old leaves. Modeling leaf growth has been extensively studied in many crops including cereals. Methods of predicting leaf area development are diverse from those dealing with the individual component processes of leaf growth, viz., leaf appearance, leaf expansion and leaf death to the models predicting leaf growth at the whole plant or whole crop levels. The concept of leaf lifetime is used in some crop simulations models to quantify the aging of the leaves after reaching thermal time to a certain amount. There is very little information about wheat aging time in the field, and most estimates of leaf lifetime are related to this observation that says on the main stem of wheat, at least 3 to 5 green leaves remains until pollination; one leaf is in the early stages of development, another leaf is completely developed and one to three leaves are aging. Quantitative information regarding leaf area development in wheat especially in environmental conditions with high temperatures for the purpose of crop modeling is scarce. Furthermore, genotypic variations have not been evaluated. Therefore, the goal of this research was to determine parameters related to leaf lifetime in wheat cultivars in warm environmental conditions.

The aim of this study was to quantify leaf lifetime of 15 different wheat cultivars. Two field experiments with 15 wheat cultivars (Atrak, Bayat, Chamran, Chenab, Dez, Ineia, Kavir, Marvdasht, Shiraz, S78-18, Yavaroos and shova-Mald) were conducted at the research farm of the Islamic Azad University of Ramhormoz Branch, south-western of Iran during 2008-9 and 2009-10 using a randomized complete block design with four replications. To determine leaf lifetime, a logistic model (Amax/[(1+exp)-a(x-b)]) was used in two stages. At first phase, changes in total plant leaf number versus growing degree days was determined, then, changes in plant senesced leaf number versus growing degree days were investigated.

The results indicate that the average of leaf lifetime based on growing degree days was 468.8 C dᵒ. This conclusion shows at optimum condition in terms of temperature, on average, a leaf lasts 468.8 C dᵒ. The average of phyllochron (the interval time between the sequential emergence of leaves on the main stem of a plant) was 84 C dᵒ in studied cultivars, upon which, the average of leaf lifetime in cultivars was 5.5 phyllochron. Hence, knowing the differences among hybrids in leaf area attributes may be useful in plant breeding, crop management and in wheat growth modeling.

 Based on the results, there were no significant differences between wheat cultivars in terms of parameters related to leaf lifetime on stem. The relationships presented in this study describe leaf lifetime under well-watered condition and reflect the effects of carbon and nitrogen availability and remobilization under these conditions. However, they do not account for the effects of shortage of carbon, nitrogen or water on leaf development. Other relationships are required to predict these effects.