Effect of mycorrhiza fungi, Trichoderma and selenium on the crop yield and antioxidant enzyme activity of strawberry

 Strawberry is one of the most economically valuable horticultural species. Strawberry production and consumption has increased due to the fruit's appealing color, flavor, and abundance of essential bioactive compounds, such as vitamin C, sugars, organic acids, anthocyanins, phenolic compounds, and antioxidant activity. Today, consideration is given to environmentally friendly and sustainable production. Due to the depletion of nutrient element accessibility or the improvement of soil organic elements in agricultural soils, as well as replant diseases, bioproducts and beneficial microorganisms must be applied (mycorrhizal fungi, and filamentous fungi). These may increase soil biodiversity, promote plant growth, and have antagonistic effects on microorganisms that reduce plant yield. Arbuscular mycorrhizal fungi (AMF) are among the most widely distributed endotrophic mycorrhizal fungi species. It is considered an eco-friendly biofertilizer because it enhances plant growth, performance, and quality. Furthermore, Trichoderma is a fungus genus commonly recognized as an agricultural biocontrol agent. Plant growth is enhanced by Trichoderma stimulation. It promoted the host's health by inducing systemic resistance and enhancing plant growth, development, and photosynthetic efficiency. In contrast, selenium (Se) is not regarded as an essential element for higher plants, but at low concentrations, it is regarded as beneficial. Se biofortification can enhance plant mineral content, growth, yield, and quality by inducing antioxidative defenses. This study evaluated the effects of AMF, Trichoderma, and Se on the crop yield and antioxidant enzyme activity of the strawberry cultivars Gaviota and Camarosa. This experiment was conducted in the research greenhouse of Shahed University, College of Agriculture in 2017. The experiment was conducted as a factorial based on a completely randomized design with three replications. Treatments included: fungi (Mycorrhiza and Trichoderma), selenium (Se, 0, 0.5, 1, 2 and 4 mg-1 kg soil) and cultivar (Gaviota and Camarosa). Fruit yield was determined at harvest. The fruits were harvested at the same ripening stage (>75% red surface color) and then transported to the laboratory immediately. Within each replication, only identical-sized, -colored, -shaped, and physically unblemished and disease-free fruits were chosen. Physicochemical characteristics of fruit were determined during harvest. 30 strawberries from each replication were used for this purpose. For fruit sampling, tissue samples consisting of both achenes and receptacles were taken from the central portion of the fruit. The samples were quickly sliced, pooled, frozen in liquid nitrogen, and stored at -80°C until their total phenolic content and catalase, superoxide dismutase, and ascorbate peroxidase activities were determined. The data were analyzed as a two-factor linear model using the PROC MIXED procedure by the SAS software. The Duncan's Multiple Range Test (DMRT) at P ≤ 0.05 was calculated to compare the differences between means following a significant ANOVA effect.  The results demonstrated that mycorrhiza and Trichoderma fungus significantly boosted plant performance. Compared to the control, Trichoderma and mycorrhizal fungi treatments increased yield by 39.6% and 27.1%, respectively. Additionally, the application of Se increased yield in comparison to the control. Phenolic compounds, ascorbate peroxidase, catalase, and superoxide dismutase activities were affected by fungi and Se treatments, with ascorbate peroxidase and superoxide dismutase activities found to be 4 mg-1 kg soil when Se was applied. The activity of antioxidant enzymes varied between cultivars, with Gaviota exhibiting greater antioxidant enzyme activity than Camarosa. Trichoderma, mycorrhizae, and Se were utilized to maximize catalase activity (4 mg-1 kg soil). Mycorrhizal fungi and Trichoderma appear to increase enzyme yield and activity by facilitating enhanced element absorption. Based on the results of this study, the use of fungi and Se at concentrations of 4 mg-1 kg soil is recommended to increase the quantity and quality of strawberries.