Fungal Endophytes Enhance Wheat and Tomato Drought Tolerance in Terms of Plant Growth and Biochemical Parameters.

Drought is a major threat to plant growth in many parts of the world. During periods of drought, multiple aspects of plant physiology are negatively affected. For instance, water shortages induce osmotic imbalance, inhibit photosynthesis, decrease nutrient uptake, and increases the production of reactive oxygen species (ROS). In this context, it is necessary to develop sustainable strategies for crops that would help mitigate these conditions. In previous studies, endophytic Zopfiella erostrata strains were found to extensively colonize plant roots, forming a profuse melanized mycelium in the rhizosphere, which could be involved in improving water uptake and nutrient mineralization in plants. The aim of this study is to evaluate the effect of different strains of Z. erostrata on stress mitigation in wheat and tomato plants grown under water deficit conditions. General plant growth variables, as well as physiological and biochemical parameters, related to oxidative status were determined. Our data demonstrate that inoculation with both Zopfiella strains had a very significant effect on plant growth, even under water deficit conditions. However, we observed an even more pronounced impact, depending on the plant and strain involved, suggesting a certain degree of plant/strain compatibility. The biochemical aspects, the accumulation of proline, the oxidative damage to lipids, and the activity of antioxidant enzymes varied considerably depending on the endophyte and the plant evaluated.

Arbuscular mycorrhiza effects on plant performance under osmotic stress.

At present, drought and soil salinity are among the most severe environmental stresses that affect the growth of plants through marked reduction of water uptake which lowers water potential, leading to osmotic stress. In general, osmotic stress causes a series of morphological, physiological, biochemical, and molecular changes that affect plant performance. Several studies have found that diverse types of soil microorganisms improve plant growth, especially when plants are under stressful conditions. Most important are the arbuscular mycorrhizal fungi (AMF) which form arbuscular mycorrhizas (AM) with approximately 80% of plant species and are present in almost all terrestrial ecosystems. Beyond the well-known role of AM in improving plant nutrient uptake, the contributions of AM to plants coping with osmotic stress merit analysis. With this review, we describe the principal direct and indirect mechanisms by which AM modify plant responses to osmotic stress, highlighting the role of AM in photosynthetic activity, water use efficiency, osmoprotectant production, antioxidant activities, and gene expression. We also discuss the potential for using AMF to improve plant performance under osmotic stress conditions and the lines of research needed to optimize AM use in plant production.

Azospirillum and arbuscular mycorrhizal colonization enhance rice growth and physiological traits under well-watered and drought conditions.

The response of rice plants to inoculation with an arbuscular mycorrhizal (AM) fungus, Azospirillum brasilense, or combination of both microorganisms, was assayed under well-watered or drought stress conditions. Water deficit treatment was imposed by reducing the amount of water added, but AM plants, with a significantly higher biomass, received the same amount of water as non-AM plants, with a poor biomass. Thus, the water stress treatment was more severe for AM plants than for non-AM plants. The results showed that AM colonization significantly enhanced rice growth under both water conditions, although the greatest rice development was reached in plants dually inoculated under well-watered conditions. Water level did not affect the efficiency of photosystem II, but both AM and A. brasilense inoculations increased this value. AM colonization increased stomatal conductance, particularly when associated with A. brasilense, which enhanced this parameter by 80% under drought conditions and by 35% under well-watered conditions as compared to single AM plants. Exposure of AM rice to drought stress decreased the high levels of glutathione that AM plants exhibited under well-watered conditions, while drought had no effect on the ascorbate content. The decrease of glutathione content in AM plants under drought stress conditions led to enhance lipid peroxidation. On the other hand, inoculation with the AM fungus itself increased ascorbate and proline as protective compounds to cope with the harmful effects of water limitation. Inoculation with A. brasilense also enhanced ascorbate accumulation, reaching a similar level as in AM plants. These results showed that, in spite of the fact that drought stress imposed by AM treatments was considerably more severe than non-AM treatments, rice plants benefited not only from the AM symbiosis but also from A. brasilense root colonization, regardless of the watering level. However, the beneficial effects of A. brasilense on most of the physiological and biochemical traits of rice plants were only clearly visible when the plants were mycorrhized. This microbial consortium was effective for rice plants as an acceptable and ecofriendly technology to improve plant performance and development.