The Effects of Drought Stress and Humic Acid on Morphological Traits, Yield and Anthocyanin of Roselle (Hibiscus sabdariffa L.)

Introduction Roselle (Hibiscus sabdariffa L.) as a medicinal plant belongs to the Malvacea family. Their active ingredient increases under water stress. Humic acid bacteria derived from humus and other natural resources have hormonal effects and can improve nutrient absorption to enhance performance especially under stress conditions .
Materials and methods This experiment was conducted in the research of agricultural education centre Jiroft in 2013. Field experiment was carried out as split plot design with three replications. Water deficit stress set as main factor with three levels (A1= Irrigation after 50, A2= 100 and A3= 150 mm evaporation from pan class A) and humic acid was in four manners (B1= non humic acid, B2= once with Irrigation, B3= once with Irrigation Once spraying, B4= once with Irrigation twice Spraying). Humic acid was used to form Irrigation spray in order to arrange with compactness (10 kg.ha-1), (250 ml/100L). In late September, which coincides with the end of the heading, plant height, inflorescence length, number of branches, stem diameter, fresh and dry weight of plant, fresh and dry weight of sepals, were examined. Wagner method was used to measure anthocyanin content sepals (Wagner, 1979). Finally, data was analyzed using SAS 9.1 and means were compared by Duncan’s multiple range test at 5% level of probability.
Results and discussion The analysis of variance showed that drought stress and humic acid had significant effect on growth parameters, vegetative and generative yield and anthocyanin. Drought stress decreased plant height, inflorescence length, stem diameterand fresh and dry weight sepals. The highest values of these traits was obtained in the first level of stress (50 mm evaporation from pan class A). Due to the reduction in mentioned properties, reducing the pressure tolerance and the subsequent reduction in drought conditions was considered as division and cell enlargement. The reduction in growth parameters by drought stress can be due to disorder in photosynthesis and reduction in photosynthetic. The impact of drought on each of growth parameters could finally lead to a change in the performance of the roselle calyx production.
Drought stress increased anthocyanin content. The highest phenolic compounds anthocyanins (0.49 μmol.g1) was obtained in three level stress (150 mm evaporation from pan class A). Antioxidant flavonoids had protective effect during drought stress and due to the role of anthocyanin in protection from sun during oxidative stress, ROS was directly removed. The results showed a significant interaction between stress and humic acid on number of branches, fresh and dry weight of plants. The highest value of these traits treatment was observed in first level stress (irrigation after 50 mm evaporation from pan class A) and in four level of humic acid (once with irrigation twice spraying). Plant height, inflorescence length, stem diameter, fresh and dry weight of sepals and anthocyanin were significantly affected by humic acid. The highest value of these traits was obtained in four humic acid (once with irrigation twice spraying). Humic acid can reduce the effects of drought, increase absorption of water and nutrient and the growth of plants by physiological changes in plant and by improving the physical, chemical and biological characteristics of soil, in order to improve growth parameters, vegetative and generative yield and anthocyanin in the experiment.
Conclusion Sufficient moisture in the soil and high genetic potential for optimum usage of the potential environment are essential for plants. The amount of humic acid due to its role in improving the nutritional conditions of the plant can play an important role in offseting the harmful effects of drought stress on the plant