Effect of drought Stresses and aerosols on yield and some physiological traits of grain sorghum (Sorghum bicolar L.)

Introduction

Abiotic stresses, in particular, water shortage pose immense challenges to crop production and can decrease crop yields by 50% worldwide (Mahajan Tuteja, 2005). Water deficit has negative impacts on growth, development and production of legumes, which may result in decreased chlorophyll a and b and increased proline content of leaf (Karimi et al., 2016). Aerosols are principal air pollutants that can greatly impact human health and plant development. This natural phenomenon, which mainly occurs in Iraq and Iran`s western regions, has exacerbated in recent years and caused a lot of damage (Marsafari, 2011). The objective of this study was to evaluate the effects of aerosol particles and drought stress on grain sorghum photosynthetic pigments, soluble sugars, proline, relative water content of flag leaf, leaf temperature and grain yield.

The research was conducted to investigate the effect of drought and aerosol stresses on morpho-physiological traits of grain sorghum (Sorghum bicolar L.) at Lorestan Agricultural and Natural Resources Research and Education Center in 2015. A split plot design based on RCBD was used with four replications. The main plots were allocated to four different irrigation regimes: watering after 60, 90 and 120 mm evaporation from pan class A. The subplots were assigned to three levels of aerosols derived from clay soil source) control treatment, 50 and 100 mg m-3 aerosol particles (. Chlorophyll a, chlorophyll b, soluble sugars, proline content, relative water content and leaf temperature were measured at flowering period and yield components and grain yield were measured at harvest time.

The results of the first year of the experiment showed that chlorophylls a and b were only affected by drought stress where they were linearly significantly decreased from 0.017 and 0.012 mg/g FW, respectively, in control treatment, to 0.0068 and 0.0065 mg/g FW in I120 treatment with increasing drought stress. Water stress triggered the production of active oxygen along with the reduction and decomposition of chlorophyll (Karimi et al., 2016). Soluble sugars and proline leaf concentration were not affected by aerosols, but were significantly affected by drought stress. Sugar content linearly and significantly increased from 4.3 mg/g under normal moisture conditions to 7.9 mg/g fresh leaf weight in I120 treatment. Proline concentrations were linearly and significantly increased from 0.25 mg/g under normal moisture conditions to 0.66 mg / g leaf fresh weight in I120 treatment. The results of two-year compound variance analysis indicated that grain number per panicle decreased but thousand grain weight increased due to drought stress. The change in grain yield was attributed to significant linear relationship and negative correlations with increasing drought stress. The highest average grain yield (8257 kg/ha) was obtained from the normal irrigation, which decreased to 6393 kg/ha under drought stress. The highest average relative content of flag leaf water was obtained from the normal irrigation, which was 2.80% and was reduced to 70.3% under drought stress.

In general, it was found that the amount of chlorophylls a and b and the relative water content of flag leaf and, as a result, grain yield were significantly decreased with increasing drought stress, but osmotic compounds (sugars solution and proline content of leaf) and leaf temperature increased significantly. Increasing drought stress decreased the number of grains per panicle and increased 1000-grain weight, but the increase in 1000-grain weight could not compensate for the decrease in the number of grains per panicle and consequently led to the decreased grain yield. Low concentration of aerosols on the sorghum leaves due to being vertical and waxy caused no serious damage to the plant's photosynthetic system and as a consequence to grain production.