Response of Agronomic and Phenological Characteristics of Bread Wheat (Triticum aestivum L.) Cultivars with Different Growth Habit to Delayed Planting

Wheat (Triticum aestivum L.) is one of the most important crops in the world as well as in Iran. It has experienced many improvements in terms of yield and quality traits during recent decades. Wheat, like energy, is known as a strategic commodity and is one of the important indicators of agriculture. This plant has the highest area under cultivation and production among other cereals in the world. Planting date is an important factor in crop production because meteorological parameters vary with changes in planting date. Delay in planting is one of the problems that is common in almost all wheat growing areas of Iran and is one of the main causes of reduced yields of wheat cultivars. Yield reduction rate varies depending on the delay in planting and cultivars, and the results of some experiments indicate that this amount sometimes reaches more than 35% of potential grain yield. Phenology and growth rate due to their effect on duration and the occurrence of different stages of development and the environmental conditions prevailing in each of these stages, are the key point of adaptation to various environmental conditions such as delayed planting date. This experiment was designed to identify the changes in yield and yield components and phenological stages of new bread wheat cultivars with different growth habits and to investigate the possibility of introducing cultivars compatible with delayed planting date in the region.

This research was conducted in two separate experiments based on a complete randomized block design with optimum planting date (6th November) and delayed planting date (6th December) on 10 new bread wheat cultivars with three replications on the research farm of the Seed and Plant Improvement Research Institute in Karaj in two years (2016-2018). The bread wheat cultivars include Pishgam, Heidari, Rakhshan, Sivand, Baharan, Sirvan, Parsi, Mehregan, Chamran 2 and Chamran. Yield and yield components such as number spike per m2, number of grain per spike, 1000-grain weight were measured at the end of the growing season to evaluate responses of the cultivars to the various planting dates. In addition, the phenological stage was recorded during the growing season.

Results indicated that delayed planting date from 15th Nov. to 15th Dec. caused a significant reduction on grain yield (from 7485 to 6066 kg.ha-1), number of spikes per m2 (from 698 to 605), number of grain per spike (from 28.5 to 25.8 seed), and 1000 grain weight (from 41.1 to 38.4 g). The interaction effects of planting date and cultivars were significant on grain yield and yield components. The highest and lowest grain yield belonged to Pishgam (7436 kg. ha-1) on optimum planting date and Chamran (5842 kg.ha-1) on delayed planting date, respectively. Delayed planting date reduced duration of planting to double ridge (from 736 to 641 GDD), planting to terminal spikelet (from 982 to 886 GDD), planting to anthesis (from 1608 to 1457 GDD) and planting to maturity (from 2456 to 2265 GDD).

Duration of different developmental stage is very important for the formation of yield components that determine the final grain yield. Although these stages are a genetic trait, but they are affected by plant growth conditions and environmental stresses, climatic factors, especially temperature and day length. Our research showed that delay in planting reduced grain yield by 18% compared to the optimum planting date because of the reduced number of spikes per m2 and vegetative and grain-filling periods.Based on the results, in cases of delayed planting date (unfavorable weather conditions, insufficient planting equipment, etc.) in Karaj region or similar climatic regions, early maturity cultivars such as Mehregan and Chamran 2 and moderate maturity cultivar like Sivand are recommended in order to minimize yield loss.