Leaf Gas Exchange, Yield and Yield Components of Wheat (Triticum aestivum L.) Cultivars as Affected by Plant Density

Determination of optimal plant density is one of the main factors that may affect crop growth and seed yield when planting is performed in the plant residues especially in conservation tillage systems. To investigate the effect of plant density on leaf gas exchange of wheat cultivars, a field split plot experiment based on randomized complete blocks design with three replications was carried out at Karaj Research Farm of Seed and Plant Improvement Institute in Iran. In this study, the main factor was three levels at plant densities (400, 500 and 600 seed per m2) assigned to main plots and five wheat cultivars (Sivand, Sirvan, Pishtaz, Pishgam and Parsi) to sub-plots. Results of analysis of variance showed that transpiration rate (E) (p<0.05), stomatal conductance (Gs) (p<0.01), net photosynthetic rate (Pn) (p<0.01) and Quantum yield (Qy) (p<0.01), number of grain per spike (GPS), seed weight (SW), seed yield (SY), biological yield (BY) and harvest index (HI) were affected by plant density and cultivar significantly. In addition, interaction effect of plant density×cultivar was significant on leaf temperature (LT) (p<0.01), intercellular CO2 concentration (Ci) (p<0.05) and biological yield (BY) (p<0.01). The results also indicated that increment of plant densities of 400 to 600 seed per m2 decreased E, Gs, Pn and Qy. Increasing plant density decreased GPS and HI. The Pishgam cultivar had the highest E and Gs, while higher values of Pn, Qy and water use efficiency belonged to Parsi cultivar. The highest value of SY was obtained from Sirvan cultivar.