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IntroductionE. purpurea is a plant that blooms in North America during the summer. It is essential for the pharmaceutical industry because it boosts the immune system and can be used for various external and internal ailments. Abiotic stresses like drought are significant problems for plant productivity. Many studies have been done on how these stresses affect agricultural plants because they cause economic losses. Drought affects plant growth and development by reducing crop growth rate, biomass accumulation, cell division and expansion, leaf size, stem elongation, root proliferation, and stomata oscillations. Although the effect of drought stress on various characteristics of coneflower has been studied in many research, few researchers have investigated the changes in the essential oil content of this important medicinal plant under drought stress. Due to a water shortage in Iran and the growing use of herbal medicines, studying how drought stress affects the composition of coneflower essential oil is crucial.Materials and methodsThis research was carried out in 2021 in the greenhouse of the Department of Horticultural Sciences, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran. The study was done as a factorial based on a completely random design with two factors of drought stress (80, 60, and 40% FC) and growth stage (10 leaves, pre-flowering, and flowering stage) in three replications. Took coneflower seeds were planted in cultivation trays. After 60 days, the seeds germinated, and the seedlings were prepared and transferred to pots. The weight method was used to determine soil moisture content. The pots were weighed daily and watered to maintain the intended level of irrigation. After the drought stress period ended, the plants with their roots were transferred to the lab, and some growth, biochemical, and phytochemical characteristics were measured.Results and discussionThe results of the analysis of variance showed that the interaction effect of irrigation levels and phenological stages was significant for the characteristics of leaf area, stem length, flower diameter, flower dry weight, chlorophyll a, chlorophyll b, carotenoid and total phenol and flavonoid of the flower and root. The results showed that drought stress caused a significant decrease in the growth characteristics, chlorophyll a, carotenoid, and increased chlorophyll b content of coneflower in different stages of growth. The concentration of coneflower's total phenol and flavonoid under severe drought stress increased by 37.58 and 25.67, respectively. Also, the antioxidant capacity of the coneflower flower increased under severe drought stress, but drought stress did not affect the antioxidant capacity of the roots. In addition, the results showed that more than 70% of the essential oil components at the time of applying the control in the 10-leaf and pre-flowering stage, and severe stress in all three stages of growth consisted of four compounds: Germacrene D, n-Dodecane, n-Tridecane, and n-Undecane. Compared to the control, most of the essential compounds of coneflower under severe drought stress decreased in the 10-leaf growth stages and pre-flowering but increased in the flowering stage. Severe drought stress caused a decrease in Germacrene D in the 10-leaf and flowering stages (41.6 and 41.3%, respectively) and increased it in the pre-flowering stage (77.2%). During drought conditions, plants reduce the number and area of their leaves as an adaptation strategy and first defense mechanism. Plants exposed to environmental stress can increase their stress tolerance by producing more phenol, flavonoid, and antioxidants. These non-enzymatic antioxidants help reduce the adverse effects of stress on plants. Based on the findings of various research, it can be said that Germacrene D, Spathulenol, β-Caryophyllene, and α-Humulene are the main components of the essential oil of coneflower. In agreement with our results, the research findings showed that severe drought stress (40% FC) caused a significant decrease in the phytochemical compounds of coneflower. Secondary metabolites are influenced not only by genetics but also by changing environmental patterns.ConclusionWith increasing drought stress levels, growth characteristics, chlorophyll a, carotenoid, and root total phenolic content of coneflower decreased significantly. Also, drought stress increased stem diameter, chlorophyll b, total phenol content, total flavonoid, and antioxidant capacity of flowers. Under severe drought stress, four compounds of Germacern D, N-dodecane, N-tridecane, and N-one-decane, which are the dominant components of the root essential oil of this plant in the present study, decreased in the 10-leaf and flowering stages but increased in the pre-flowering stage. In general, it can be concluded from the current research results that applying drought stress can help improve coneflower root essential oil composition.

Contamination of ecosystems upon excessive use of pesticides and emergence of resistance in pathogens to these chemicals makes continuous research on development of new control methods and strategies to combat plant pathogens an essential task. Plant disease resistant genes are useful genetic resources that can be employed to develop resistant varieties as the best alternative to other control measures. The present investigation was carried out to analyze the interaction of two major rice cultivars grown in Northern provinces, with Rhizoctonia solani, the causative agent of rice sheath blight disease. Binam and Khazar known as the resistant and susceptible cultivars, respectively, were inoculated and their reaction to R. solani determined. The lesions in the sheath of the susceptible cultivar were twice in length compared to those on the resistant cultivar. Analysis of data by the Student’s T test showed existence of significant difference (P value < 0.05) between the two cultivars. To determine the expression profile of the genes involved in resistance to R. solani, samples were taken from leaves of two weeks old seedlings in different time courses post inoculation. RNA was extracted from the samples and analyzed by quantitative real time PCR. Results of the present study indicated that expression rates of PR-5, Proxidase, PR-10, Defensin, Thionin, and NH-1 in resistant genotype (Binam) increased greatly after inoculation with R. solani when compared to Khazar cultivar. The outcomes of this study also suggest that the genes under study are involved in resistance mechanisms of rice against sheath blight disease.

Chilling temperatures lead to numerous physiological disturbances in the cells of chilling-sensitive plants and result in chilling injury and death of tropical and subtropical plants such as watermelon. In this study, the possibility of cold stress tolerance enhancing of watermelon seedling (Citrullus lanatus) by exogenous application of Salicylic acid (SA) was investigated. SA was applied through seed soaking or foliar spray at 0, 0.5, 1 and 1.5 mM concentration. After SA treatment, the seedlings were subjected to chilling 5 h/day at 4°C for 5 days. Statistical analysis showed significant effects of the application methods and SA concentrations on plant growth parameters, photosynthetic pigments, electrolyte leakage, proline and chilling injury index. SA application improved growth parameters and increased chlorophyll content of watermelon seedling subjected to chilling stress and provided significant protection against chilling stress compared to non-SA-treated seedlings. Although two SA application methods improved chilling stress tolerance, seed soaking method provided better protection compared to foliar spray method. SA ameliorated the injury caused by chilling stress via inhibiting proline accumulation and leaf electrolyte leakage. The highest cold tolerance was obtained with 0.5 mM SA application. Results indicate that SA could be used effectively to protect watermelon seedling from damaging effects of chilling stress at the early stages of growth.

Chilling temperatures lead to numerous physiological disturbances in the cells of chilling-sensitive plants and result in chilling injury and death of tropical and subtropical plants such as watermelon. In this study, the possibility of cold stress tolerance enhancing of watermelon seedling (Citrullus lanatus) by exogenous application of Salicylic acid (SA) was investigated. SA was applied through seed soaking or foliar spray at 0, 0.5, 1 and 1.5 mM concentration. After SA treatment, the seedlings were subjected to chilling 5 h/day at 4°C for 5 days. Statistical analysis showed significant effects of the application methods and SA concentrations on plant growth parameters, photosynthetic pigments, electrolyte leakage, proline and chilling injury index. SA application improved growth parameters and increased chlorophyll content of watermelon seedling subjected to chilling stress and provided significant protection against chilling stress compared to non-SA-treated seedlings. Although two SA application methods improved chilling stress tolerance, seed soaking method provided better protection compared to foliar spray method. SA ameliorated the injury caused by chilling stress via inhibiting proline accumulation and leaf electrolyte leakage. The highest cold tolerance was obtained with 0.5 mM SA application. Results indicate that SA could be used effectively to protect watermelon seedling from damaging effects of chilling stress at the early stages of growth.