Effects of vermicompost and nano silicon on yield and some physiological and biochemical traits of safflower (Carthamus tinctories L.) under irrigation withholding condition

Drought stress is the most influential factors affecting crop yield particularly in irrigated agriculture in arid and semiarid regions. This stress induces various biochemical and physiological responses in plants as a survival mechanism (Tas and Tas, 2007). Drought stress have a direct impact on the photosynthetic apparatus, essentially by disrupting all major components of photosynthesis including the thylakoid electron transport, the carbon reduction cycle and the stomatal control of the CO2 supply, together with an increased accumulation of carbohydrates, peroxidative destruction of lipids and disturbance of water balance (Allen and Ort, 2001). It breaks down the balance between the productions of reactive oxygen species (ROS) and the antioxidant defense system causing the accumulation of ROS which induces oxidative stress to protein, membrane lipids and disruption of DNA strands (El Tayeb, 2006). Several strategies have been developed in order to decrease the toxic effects caused by severe water limitation on plant growth. Among them the use of vermicompost and nano silicon play a key role in yield improvement. The aim of this study was to investigate the effects of vermicompost and nano silicon application on yield and some physiological and biochemical traits of safflower under irrigation withholding conditon.

In order to study the effect of vermicompost and nano silicon on yield and some physiological and biochemical traits of safflower (Carthamus tinctories L.) under irrigation withholding conditon, an experiment was conducted as factorial based on randomized complete block design with three replications in research farm of University of Mohaghegh Ardabili during 2019-2020. Factors experiment were included irrigation levels (full irrigation as control, irrigation withholding in 50% of heading bud and flowering stages as severe and moderate water limitation respectively) according with 55 and 65 BBCH code, foliar application nano silicon (foliar application with water as control, application of 25 and 50 mg.l-1 nano silicon) and application of vermicompost (no application of vermicompost as control, application of 4 and 8 t.ha-1). Vermicompost was purchased from the Gilda corporation. The safflower cultivar "Padideh" was used in the experiment with plant density of 40 seeds m-2. Chlorophyll and carotenoids were obtained based on method of Arnon (1967). The quantum yield was measured by the uppermost fool expanded leaf using a fluorometer (chlorophyll fluorometer; Optic Science-OS-30 USA). For this purpose, the plants adapted to darkness for 20 minutes by using one special clamp then the fluorescence amounts were measured in 1000 (µM photon m2s), and calculation was performed using following formula (Arnon, 1967):ØPSII = (Fm-F0)/Fm ØPSII; quantum yield amount of photosystem II, Fm or maximum fluorescence after a saturated light pulse on plants adapted to darkness and F0, the minimal fluorescence in the light adapted, which was determined by illumination with far-red light. To measure the enzyme activity, 0.2 g of fresh tissue was crushed by using liquid nitrogen and then one ml of buffer Tris-HCl (0.05 M, pH=7.5) was added. Obtained mixture centrifuged for 20 min (13000 rpm and 4 ºC), then supernatant was used for enzyme activity measurements. Catalase, Peroxidase and Polyphenol Oxidase activity was assayed according to Karo and Mishra (1976). Also, the evaluation of protein carried out by Bradford (1976) method, 0.2 g of plant tissue was squashed with 0.6 ml extraction buffer and was centrifuged at 11500 rpm for 20 minutes at 4 °C. The supernatant was transferred to the new tubes and centrifuged for 20 minutes at 4000 rpm. To measure the protein amount, 10 µl of obtained extract was added to 5 µl Bradford solution and 290 µl extraction buffer and the absorbance rate was read at 595 nm.Statistical analysis: Analysis of variance and mean comparisons were performed using SAS ver 9.1 computer software packages. The main effects and interactions were tested using the least significant difference (LSD) test at the 0.05 probability level.

The results showed that application of the highest nano silicon level under full irrigation increased chlorophyll a and chlorophyll b (74 and 145% respectively) in comparison with no application of nano silicon under irrigation withholding in heading bud stage. Means comparison showed that irrigation withholding in booting bud at the highest vermicompost level increased proline and soluble sugars content (149 and 99% respectively) and antioxidant enzymes activity such as catalase, peroxidase and polyphenol Oxidase (103, 82 and 94% respectively) in comparison with no application of vermicompost under full irrigation. Also, the highest vermicompost level under full irrigation increased chlorophyll a, quantum yield and grain yield (61, 62 and 119% respectively) in comparison with no application of vemicompost under irrigation withholding in heading bud stage.

It seems that the application of vermicompost and nano silicon can increase grain yield of safflower under water limitation conditions due to improving physiological and biochemical traits.