Abstract
Introduction: Analysis of plant response to environmental changes and agronomic management including changes in planting history based on mathematical models is an efficient method for predicting performance. Achieving high yield in wheat is possible by matching plant growth and reproductive stages with favorable environmental conditions by choosing planting dates and appropriate genotypes. Observance of agricultural technical principles such as seed rate, planting date, growth period and suitable cultivar are important factors that have a significant impact on cultivar efficiency. So that the set of environmental factors that occurred at that time would be appropriate for the emergence, establishment and survival of the seedling, while each stage of plant growth with conditions desirable. The best cultivar in each region is the number that will complete its growth stages in the current time or season of growth in the region and when considering the type of cultivar used and the planting decision, the potential risks should be considered.
Materials and methods: Field experiment was conducted as a factorial based on randomized complete block design with three replications in 2010-2011 in rainfed conditions in Agricultural Research Station of Gonbad-e-Kavous. The test factors included: sowing date (December 17, January 3, January 20 and February 6) and spring genotypes (Kohdasht, Zagros, Line 17, Pearl and N-80-19). For measure growth factors including dry matter, leaf area and crop growth rate 6 to 7 plants per 14 days intervals during the growing season were collected. Dry weight of green, yellow and fallen leaves, stems and clusters were individually measured after placing the samples in the oven at 75°C for 48 hours (to reach constant weight).
Results: The results revealed that the growth indices like cumulative dry matter, maximum leaf area and crop growth rate were decreased with a delay in planting. The highest leaf area index (4.98) and crop growth rate (29.64 g/m2/day) were produced at December 17th planting date belonging to Line 17. The results of this study showed that in all genotypes from emergence stage to pollination, with increasing the temperature mean and day length, the rate of development increased and the number of days required for each development stage decreased. Also, in all genotypes by delayed planting and increasing of temperature, the minimum number of days for each developmental stage decreased. The maximum leaf area index in different genotypes on the planting dates in this study was before clustering (pregnancy stage). In different planting dates, with increasing day length and temperature increase, the time to reach 50% of the maximum dry matter decreased, so that in the Koohdasht, Line 17, Zagros, Morvarid and N-80-19 genotypes at sowing date February 6 compared to the planting date of December 17th was 34.59, 24.31, 35.71, 30.32 and 27.92%, respectively. In all genotypes, the maximum crop growth rate (CGR) and the time to reach the maximum CGR with delayed planting decreased. The highest CGR was observed on the December 17th planting date on the Line 17 (29.64 g/m2) and the lowest CGR on the February 6th planting date on Line 17 (14.7 g/m2/day).
Conclusions: In general, the results of this experiment showed that there is a difference between the different wheat cultivars proposed in the same climate in terms of length of phonological stages. Although differences between cultivars are partly due to genetic differences between them, but the effect of environmental factors on their growth and development, especially in the late stages of growth, should not be neglected. Since the main difference of the product in different planting dates is due to in different light and temperature conditions at least in the early stages of growth and development. These cultivars have more flexibility and self-control in responding to changing environmental conditions using different mechanisms.
Keywords: Maximum leaf area, Crop growth rate, Wheat bread, Cumulative dry matter |
