Effect of mycorrhiza fungi and plant growthpromoting rhizobacteria (PGPR) on antioxidant capacity and some morphophysiological traits of medicinal marigold (Calendula officinalis Linn.) under drought stress

Calendula officinalis, the pot marigold, ruddles, common marigold is a plant in the genus Calendula of the family Asteraceae. It is probably native to southern Europe. It is also widely naturalised further north in Europe and elsewhere in warm temperate regions of the world. Calendula is applied to the skin to reduce pain and swelling and to treat poorly healing wounds and leg ulcers. It is also applied to the skin for nosebleeds, varicose veins, hemorrhoids, inflammation of the rectum, ear infection, gum disease, peeling lips, diaper rash, vaginal yeast infection, and inflammation of the lining of the eyelid (conjunctivitis). Essential oil of calendula has been used as an insect repellant. One of the major limiting factors for plant growth is water availability. Drought affects many aspects of plant physiology to reduct plant growth and photosynthesis. Mycorrhiza fungi colonize the roots of host plants and perform absorption services for the plant. Various studies have demonstrated that plants associated with Mycorrhiza fungi show increased uptake of various materials from the soil, including water, and macro and micronutrients. As a result, VAM fungi improve their host plants’ ability to grow under conditions of drought stress or in mineral deficient soils. The bacteria that can promote plant growth, that is, include those that are free-living, those that form specific symbiotic relationships with plants, bacterial endophytes that can colonize some or a portion of a plant’s interior tissues. Growth-promoting bacteria may promote plant growth directly usually by either facilitating resource acquisition or modulating plant hormone levels, or indirectly by decreasing the inhibitory effects of various pathogenic agents on plant growth and development, that is, by acting as biocontrol bacteria.

This research was carried out in order to investigate the effect of Mycorrhiza fungi and some growth-promoting bacteria on Calendula officinalis var. Pacific beauty orange under drought stress conditions in 2017-2018 in Faculty Agriculture, Ferdowsi University of Mashhad in a factorial experiment based on completely randomized design with 4 replications. The first factor was drought stress in two levels (100 and 50% crop capacity) and the second factor was the use of bio fertilizer in 8 levels including: Pseudomonas fluorescens (Ps), 2. Azotobactore chroococcum (Az), 3. Mycorrhizal fungus (M), 4. Ps + M, 5. Az + M, 6 Ps + Az, 7. Az + Ps + M, 8. Control (non-use of bacteria and fungi). At the end of the experiment morphophysiological and biochemical traits of the plant were measured. The height and diameter of the flower were measured by digital caliper. Number of flowers, number of leaves and number of lateral branches were counted. shoot and root fresh weight was weighed after the separation of the plant from the pot in a laboratory with a digital scale of 0.001. then plants were ejected from the pot, root length was recorded. The maximum efficiency of the photocysteine II in the plant was measured by a fluorometer (FL-OS model) and for measuring chlorophyll index (SPAD-502) using Spad. The relative leaf water content, ion leakage and antioxidant capacity were measured.The statistical analysis of the test data and the comparison of the averages at the probability level of 5% error based on the LSD test was performed using JMP-8 statistical software and drawing charts with Excel 2010 software.

 The results showed that drought stress caused a decrease in growth traits in Calendula. So, by decreasing soil capacity from 100 to 50% FC, number of leaves, number of flowers, flower diameter, shoot and root fresh weight, number of lateral branches, Spad and relative leaf water content decreased and Antioxidant capacity increased compared to control treatment. Application of growth stimulating bacteria resulted in improved traits measured in the plant under stress and non-stress conditions. Application of Pseudomonas fluorescens alone or in combination with mycorrhizal fungus under stress conditions (50% FC) resulted in improved growth characteristics in Calendula plant. In terms of number of leaves, number of flowers, flower diameter, number of lateral stems and Spad, improved by application of Pseudomonas fluorescens alone in soil or its combination with mycorrhizal fungus under stress conditions. PGPR directly affects plant growth by facilitating the availability of nutrients such as nitrogen, phosphorus and iron. These nutrients are critical to plant biochemistry, and without them plant growth is limited. While nitrogen, phosphorus and iron may be abundant in the soil, they are often found in a form the plant can’t utilize. PGPR convert those nutrients to the form the plant can use. Actually, PGPR can produce plant hormones like auxins, gibberellins and cytokinins that stimulate plant root and shoot growth in exchange for food sources from the plant. Also, Mycorrhiza fungi can help plants to cope with the detrimental effects of soil water deficit acting, directly or indirectly, on plant functionality both above- and belowground. At the levels of both leaves and roots, the osmotic stress usually caused by drought is counteracted by mycorrhizal plants through biochemical changes that mostly include increased biosynthesis of metabolites (mainly proline and sugars) that act as osmolytes. These compounds contribute to the lowering of the osmotic potential, and in turn, of the leaf water potential. Finally, it seams that the use of Pseudomonas fluorescens in soil alone or in combination with mycorrhizal fungi under drought stress conditions can improve plant growth and increase plant efficiency under drought stress conditions.