Eco-physiological, Biochemical and Herbicidal Characteristics of Lavandula stricta, Cassia obovata, Cocculus pendulus and Solanum xanthocarpum

Introduction  Lavandula stricta, Cassia obovata, Cocculus pendulus, and Solanum xanthocarpum are among the species that can be grown in Bushehr province, and so far, there is no report describing the ecophysiological, herbicidal and biochemical characteristics of these species in Iran. In recent decades, many chemical herbicides have been used to control weeds in agricultural ecosystems. Despite the many benefits of these herbicides, their improper use has caused devastating effects on the environment and agricultural production and ultimately has harmed human health. At present, the approach of developed countries is to use non-chemical methods and natural materials (biocides) to control weeds. Bushehr province with an area of about 252,653 Km2 in southern Iran and the Persian Gulf and at an altitude of 0 to195 meters above sea level. The average rainfall in Bushehr province is 250 mm. Bushehr province has a great variety in terms of having medicinal plants that allopathic substances and secondary metabolites of these plants have received less attention. Therefore, the identification of secondary metabolites and plants with allopathic properties is very important for the production of biological herbicides.   Materials and Methods  This study was conducted to evaluate the eco-physiological, biochemical and herbicidal characteristics of Lavandula stricta, Cassia obovata, Cocculus pendulus and Solanum xanthocarpum. The plants were collected in April and May 2019. The location was situated in Kangan and Dashti, Bushehr Province, Iran. The ecological characteristics of the four areas such as latitude and longitude (UTM) and altitude were also recorded. Also, in order to determine the physicochemical properties of the soil in the collection areas of the studied plants, samples were taken from 15 different points of plant growth, from a depth of 0-30 cm and their properties were reported. In order to investigate the phytotoxic activity of the studied plants on germination and growth characteristics of Malva sylvestris and Chenopodium album in laboratory conditions, the seeds were first disinfected in 5% sodium hypochlorite for 5 minutes. Then the seeds were washed for 15 minutes and then dried at room temperature. In this study, Solanum xanthocarpum juice and alcoholic extracts of Lavandula stricta, Cassia obovata and Cocculus pendulus were used to investigate the phytotoxic properties and biochemical traits. From the extracts, concentrations of 0 (distilled water), 200, 400, 600, 800 and 1000 µl.L-1 were prepared and added to Petri dishes containing 25 seeds. In order to germinate the seeds, Petri dishes containing the extracts related to the extract were placed in suitable light conditions at a temperature of 25°C. Two weeks after treatment, germination percentage (%), germination rate index (number of day), radicle and plumule length (cm) and allopathic index were measured. Determination of free radical scavenging was performed by using the DPPH test. The samples’ absorptions were read at a wavelength of 517 nm with Epoch Microplate Spectrophotometer, BioTek Instruments, Inc., USA. Measuring the total phenols was performed according to Folin’s reagent method and the use of gallic acid as standard by using a spectrophotometer at the wavelength of 765 nm. Total flavonoid content was measured using a spectrophotometer at a wavelength of 510 nm through a standard curve of quercetin from Sigma-Aldrich. Flavones and flavonols were measured using 2% aluminum chloride and methanol at 425 nm. To isolate and measure the amount of polyphenols, an HPLC Agilent HPLC 1200 series model was used. Data were analyzed by using Duncan’s multiple range test (P< 0.05) by SAS, version 9.4 for Windows.   Results and Discussion  Among the studied plants, the highest  and lowest amount of total phenol was found in Cocculus pendulus and Cassia obovata, respectively. The results showed, the highest amount of the total flavonoid in the extract, was achieved in Lavandula stricta plants collected in Kangan. The lowest (0.37 mg QUE. 100 g-1 DW) and highest (2.79 mg QUE. 100 g-1 DW) amount of flavon and flavonol was found in Cassia obovata and Cocculus pendulus, respectively. Also, antioxidant activity (I%) for Cocculus pendulus, Lavandula stricta and Solanum xanthocarpum were 77, 57 and 35%, respectively. Although, the lowest amount of antioxidant activity was found in Cassia obovata plants collected in Dashti. The results showed, the Lavandula stricta plants collected in Kangan had p-coumaric acid (PC) and ellagic acid (EA) by 0.565 and 1.28 mg g-1 DW. Among the phenolic acids evaluated, only catechin (0.262 mg g-1 DW) and p-coumaric acid (0.163 mg g-1 DW) were observed in the Cocculus pendulus plants collected in Kangan. The Cassia obovata plants collected in Dashti, had ellagic acid by 0.915 mg g-1 DW. The results of this study showed that the phenolic compounds identified in Solanum xanthocarpum juice were caffeic acid, chlorogenic acid, pi-coumaric acid, vanillin and hesperidin. Chlorogenic acid was the predominant phenolic compound by 457 mg g-1 DW. Laboratory results showed Cocculus pendulus and Solanum xanthocarpum extracts had the most inhibition effect on the germination and growth of Malva sylvestris at the concentration of 1000 µl L-1.   Conclusion  In this study, as the concentration of the extracts increased, the germination percentage, germination rate index (GRI), radicle and plumule lengths of Chenopodium album decreased significantly. Moreover, Solanum xanthocarpum juice showed the highest inhibition effect on Chenopodium album growth and germination at 1000 µl L-1. Due to the high potential allelopathy of the Cocculus pendulus and Solanum xanthocarpum, they can be used for Malva sylvestris and Chenopodium album control. Also, Cocculus pendulus extract can be used as a natural antioxidant source in related industries.