Comparison of old and new dryland wheat cultivars in response to different planting dates

Sowing date is the variable with the largest effect on crop growth and its yield (Hundal et al., 1997). Planting the suitable variety at the right time results in flowering phase when the risk for freeze damage is the lowest and before heat stress during flowering and grain filling stages (Khichar & Niwas, 2006). Adequate soil moisture especially in dryland conditions are also important. Correctly matching the time at which growth stages of crop occur with the environmental requirements is key to maximize growth and yield (Hay et al., 1986; Dadashi & Khajehpour, 2004). Thus, producers have to choose the appropriate variety for a specific planting time for the optimum flowering time and thereby, the highest possible yield. Early planting can improve crop establishment but may cause early flowering, which increases the risk for frost damage. Early planting is more prone to pests and diseases. Delayed planting will reduce yield and growth as flowering and maturity stages may occur in hot, dry conditions. Generally, the time of planting varies depending on the climatic condition of the region and the variety to be grown. Different varieties of wheat are sensitive to change in environmental conditions where the crop is being grown. Therefore, it is necessary to study the genotype × environment interaction to identify the varieties which are stable in different environments especially under dryland farming.
Wheat (Triticum aestivum L.) is the third leading crop in the world after rice (Oryza sativa L.) and corn (Zea mays L.). The rising population and the rapid growth of the economy have resulted in an increasing demand for wheat in the following decades.  

This experiment was conducted as split plot based on complete randomized block design (CRD) in with three replications at the Dryland Research Station of North Khorasan, Shirvan during the growing season of 2015-2016. The main and sub factors were allocated to planting methods (2 October (T1), 1 November (T2) and 1 December (T3)) and seven cultivars (such as sardari (old cultivar), Sabalan (old cultivar), Ohadi (modern cultivar), Homa (modern cultivar), Karim (modern cultivar), Azar II (old cultivar) and Cross Sabalan (old cultivar)), respectively. Investigated traits were plant height, days No. to flowering, days No. to maturity, No. of fertile spike per m2, No. of grain per spike, No. of grain per m2, 1000-grain weight, grain yield, biological yield and harvest index.
The treatments were run as an analysis of variance (ANOVA) to determine if significant differences existed among treatments means. Multiple comparison tests were conducted for significant effects using the Duncan test.

Results showed that the simple effect of planting date was significant on plant height, days No. to flowering, days No. to maturity. Plant height, days No. to flowering, days No. to maturity, No. grain per m2, 1000-grain weight, grain yield and biological yield were significantly affected by cultivar. Interaction effect between planting date and cultivar had significant effect on No. of fertile spike per m2, No. of grain per m2, 1000-grain weight and grain yield. The highest and the lowest No. of grain per m2 were observed for Ohadi+T2 with 4149 grain.m-2 and Karim+T1 with 1309 grain.m-2, respectively. The highest biological yield was related to Ohadi with 3465 kg.ha-1. The maximum and the minimum grain yield was obtained in Ohadi+T2 with 1639 kg.ha-1 and Karim+T1 with 297.8 kg.ha-1, respectively.

Growth, yield and yield components of wheat were significantly influenced by planting time and cultivar. Early plantings experienced low early season temperatures which reduced biomass and yield. Conversely, late plantings experienced higher summer temperatures that reduced time to reach maturity. Planting date of 1 November had the highest grain yield to other planting dates. The early or late planting significantly reduced the crop yield and yield components. The maximum yield and yield components was related to Ohadi