Effect of mycorrhizal fungi on growth and absorption of nutrients of Mexican marigold (Tagetes minuta L.) under salinity stress

Introduction Salinity stress is one of the factors reducing yield and production in crops, horticulture and medicinal plants in the world. One of the suitable solutions for improving salinity tolerance in horticultural products is the use of arbuscular mycorrhiza. They have the stimulant effect of plant growth. They increase resistance to drought stress, salinity, pathogenic agents, soil contamination and heavy metals by increasing the absorption of nutrients such as phosphorus, nitrogen and some elements of low consumption, increasing water absorption and production of hormones. Materials and methods In order to evaluate the effect of mycorrhizal fungi on morphophysiological and biochemical characteristics of Mexican marigold (Tagetes minuta) under salinity stress, a pot factorial experiment based on completely randomized design with three replications was performed in the horticulture greenhouse of Agriculture Faculty, Ferdowsi University of Mashhad in 2017. The first factor using mycorrhizal fungi at three levels (without inoculation, Rhizophagus intradices and Funnetiformis mosseae) and the second factor included four levels of irrigation with salinity water (0, 40, 80 and 120 mM NaCl. The inoculum of mycorrhiza was mixed before planting the seedlings. Afterwards, the seedlings were transferred to the pot. Saline treatment was started at the four-leaf stage and performed three days a week. Saline treatment was done forty days. Measurement of the traits was performed forty days after beginning stress on the plant. The plant height, number of lateral branches, number of nodes, stem diameter were measured. Also, at the end of the experiment, nitrogen, sodium, potassium, magnesium, iron, phosphorus, manganese, zinc, calcium and chlorine were measured. Result and discussion The results showed that all of the growth characteristics significantly decreased under salinity and application of mycorrhiza cause to adjustment harmful effects of salinity and tolerance of plant to salinity. The highest nodule number (12.89), stem diameter (7.49 mm), height (65.75 cm) and lateral branches number (23.33) were obtained at the treatment without salinity with using mycorrhizal fungus Rhizophagus intradices. Salinity increased the amount of phosphorus, calcium, sodium, chlorine and nitrogen in the leaf and decreased the amount of potassium, manganese, zinc and leaf iron. The highest amount of phosphorus of leaf (8.5 mg / g of leaf dry weight) was observed in the highest salinity stress and application of Funnetiformis mosseae, the highest sodium content (12.33 mg/g leaf dry weight) and chlorine (63.09 mg Kg dry weight of leaves) was observed in 120 mM salinity without mycorrhizal. However, the highest amount of potassium (6.23 mg /g leaf dry weight) was observed in the treatment without salinity and without mycorrhizal application, the highest amount of manganese (143.91 mg/kg dry weight) in 40 mM salinity and application of Funnetiformis mosseae and the highest amount of zinc (7.12 mg/kg dry leaf) were recorded in salt free treatment and application of Funnetiformis mosseae. Salinity stress reduces cell growth through restrictions on the absorption of nutrients, plant nutrient deficiency and toxicity of food elements. In addition, salt stress reduces the production of carbohydrates and thus reduces the growth of various plant components. The higher the salt concentration, the more significant the growth is. Mycorrhizal plants have better growth compared to non-microscopic plants in soil salinity conditions. Mycorrhiza fungus stimulates plant growth by increasing the absorption of nutrients such as phosphorus, nitrogen, and some elements of low consumption, increasing water absorption and production of plant hormones and increasing plant resistance under stress conditions. Conclusion The results showed that all vegetative traits reduced due to salt stress and mycorrhizal application reduce the harmful effects of salinity and increase the resistance of the plant to salinity. Mycorrhizal has an irritating effect on plant growth. Increases plant resistance to salinity by increasing the absorption of nutrients such as phosphorus, nitrogen and some elements of low consumption, increasing water absorption and production of plant hormones. According to the results of this study, the use of mycorrhizal is an appropriate strategy to increase the resistance to salinity in plants.