Physiological bases of shade tolerance in wheat varieties

Light is the main environmental factor which regulates growth and development of crop plants. Decrease in light intensity due to shading adversely affects plant growth and development. The present study was conducted to analyze the effect of varying degree of shades on physiological characteristics and yield of wheat crop. Two shading treatments were applied i. e. 33% shading (L1) and 66% shading (L2) with full sunlight as control (L0). The experiment was conducted for 2 years during the winter seasons of 2010-2011 and 2011-2012 in a split-plot design with three replications with shading treatments in the main plot and five varieties of wheat in the sub plots. The findings of the study showed that photosynthetic rate, stomatal conductance and transpiration rate at 10 days after anthesis (DAA) were significantly reduced while the intracellular CO2 concentration (Ci) increased with increase in shading during both the years. Grain yield of all the wheat varieties decreased with increase in shading during both the years. Varietal differences in grain yield under shading are discussed in relation to Pn rates and stomatal conductance.