Investigating the effects of mycorrhizal fungi and drought stress on nutrient absorption efficiency and water relations in green bean plants

Dissertation for Master Degree in Agricultural Engineering

Agricultural Orientation

Abstract:

Drought stress is one of the most important factors limiting the growth of agricultural plants, which adversely affects crop performance. One of the methods that have been used in recent years to deal with dehydration and drought stress in many plants is the use of various types of microorganisms. It is useful like mycorrhizal fungi. Mycorrhizal fungi, having a wide hyphal network and increasing the surface area and speed of root absorption, increase the efficiency of plants in absorbing water and nutrients, especially the less mobile elements phosphorus, zinc, and copper, and improve their growth.

The coexistence of mycorrhizal fungi with plant roots through improving the absorption of nutrients can cause a positive reaction of plants, especially in drought stress conditions. In order to investigate the effect of mycorrhizal fungi on nutrient absorption efficiency and water relations in green bean plants under drought stress, a pot experiment was conducted in 2012 in the form of a completely randomized design in the form of a factorial experiment with three replications in the greenhouse of Semnan Education Center. The test factors included stress treatment at three levels, T0 humidity of field capacity, T1 humidity of 50% of field capacity and T2 humidity of 25% of field capacity and mycorrhizal fungus inoculation treatment at three levels (without inoculation M0, type one M1 and type two M2) was done in 3 replications.

The results showed that drought stress had a significant effect on the evaluated traits. So that with the decrease in soil moisture, leaf area, wet and dry weight of roots and shoots, the amount of chlorophyll and the concentration of nutrients decreased. The comparison of the results showed that inoculation with mycorrhizal fungi significantly increased the growth indicators, leaf area, phosphorus, potassium, and nitrogen content of the green bean plant under drought stress conditions compared to the uninoculated plant, but the amount of chlorophyll a, chlorophyll b, and total chlorophyll decreased. The height of the plant was not affected by any of the treatments. The dry weight of the shoot and root of the plant inoculated with both types of fungi was significantly higher compared to the non-inoculated plants at all humidity levels. The water relations of the plant, including the relative water content of the leaves, were strongly affected by drought and decreased, but the inoculation of mycorrhizal fungi increased the relative water content of the leaves. The effect of GLOMUS intradices fungus in reducing the effect of drought. And the better performance of the plant was more than the GLOMUS mosseae mushroom and it has more symbiosis with the plant root. Therefore, it can be concluded that the use of mycorrhizal fungi increases tolerance to drought stress and increases yield in green bean plants. Keywords: mycorrhizal fungi, Glomus mosseae, Glomus intradices, drought stress, green beans, agricultural capacity, growth characteristics. First: Introduction and Generalities

Introduction:

Environmental stress is the most important factor reducing the yield of agricultural products worldwide. If environmental stresses did not occur, the actual yields should be equal to the potential yields of the plants. While in many crops, the average actual yield of plants is 10-20% of their potential yield. In certain parts of the globe, due to the specific geographical location, stress factors have a greater negative impact on the production of agricultural products, and agriculture in those areas is carried out with higher costs and lower yields. (2013, Wang et al)

Among the environmental stresses, drought is an acute problem, which has affected about two million square kilometers of land that can be used for agriculture, and therefore it is considered a major limiting factor in plant production all over the world. On the other hand, the increase in the drying of agricultural lands is widely expected, so that 30% of lands in the next 25 years and more than 50% of them in 2050 will be removed from the cycle of plant production in the agricultural environment due to the development of drought (Wang et al., 2013). On the other hand, Iran is a dry and semi-arid land with very little rainfall, so that the average annual rainfall is around 274 mm. Compared to the average rainfall on the surface of the earth (about 860 mm), this amount is very low, which indicates that drought in Iran is a climatic reality (Alizadeh, 1999). Bloom stated that drought is a multidimensional stress that affects plants at different organizational levels.At the plant level, the response to drought stress is complex, because it is a reflection of the integration of stress effects and related responses at all lower organizational levels, in space and time. Blum, 1996). Singh et al. reported that drought as the most important factor controlling the yield of crops affects almost all plant growth processes. Drought is considered as the most important non-living factor limiting the growth and performance of plants (Singh et al., 1997).

To overcome the problem of soil dryness, biological solutions are one of the basic solutions that should be considered. Arbuscular mycorrhizal fungi play an important role in improving the nutrition and growth of plants in dry conditions (Singh et al., 1997). Mycorrhizal fungi, having a wide hyphal network and increasing the surface and absorption rate of the roots, increase the efficiency of plants in absorbing water and nutrients, especially phosphorus, zinc, and copper, and improve their growth (Marschner & Dell, 1994). Cereals are considered the second source of food for humans (Shahram and Danshi, 2004). Beans are one of the most important groups of plants. About 60% of beans are produced in developing countries under drought conditions (Costa Francesa et al., 2005). Beans are one of the most important species of the Leguminous family. Vigna is native to America and Asia respectively. Beans are cultivated in five continents of the world, and the world's cultivated area is about 24 million hectares and its average yield is about 500 kg per hectare.

Bean is one of the most important crops of the legume family, which is considered one of the most important sources of protein and calories in human nutrition in the modern world (Phaseolus vulgaris L.), so that bean seeds contain 20-25% protein and 50-56% carbohydrates (Graham). and Ranalli, 1997) compared to other grains, beans have 2 to 3 times more protein and 10 to 20 times more protein compared to starchy plants (Magnoon Hosseini, 1375). Currently, due to the mentioned importance, the cultivated area of ??this plant is increasing in the world, according to published statistics, the cultivated area of ??this plant is more than 24 million hectares with an average global yield of about 600 kg per hectare, and the cultivated area of ??this plant is increasing. In Iran, 125 thousand hectares have been reported with an average yield higher than the world average yield of about 1470 kg per hectare (Ghafari Khaliq, 1379)

The mechanisms of concentration and transfer of nutrients in plants, such as mass flow, diffusion or concentration and transfer by osmosis, are all a function of the amount of moisture in the soil and roots, and in case of a decrease in humidity, the intensity and concentration of nutrients undergo changes and transformations. (Taiz and Zeiger, 1998)

Mycorrhizal fungi will be able to moderate the adverse effects of drought stress in plants (Auge, 2001)

1-1- Objectives of the research project:

In this research, considering the sensitivity of the bean plant to drought stress and the effects of mycorrhization of beans, the effect of two species of Glomus intradices and Glomus mosseae fungi on drought stress tolerance conditions is investigated and It should be determined whether both types have the same effects on the plant. Will the absorption of water and nutrients increase in the conditions of symbiosis under stress? Will the performance of the plant be affected by the symbiosis and will it improve? 1. Investigating the effect of mycorrhizal fungi on the improvement of plant root growth and the efficiency of absorbing water and nutrients under drought stress conditions. 2. Determining the appropriate mycorrhizal fungus species that is able to increase the plant's tolerance to drought stress. Beans increase root growth and reduce drought stress. 2- The symbiosis of mycorrhizal fungi increases the absorption of useful elements. 3- There is a difference between mushroom species in terms of their effect on plant growth. 4- The symbiosis of mycorrhizal fungi increases water absorption. Green

Bean is a herbaceous plant from the legume family. Its leaves are green, broad, large and pointed, heart-shaped. Its flowers are white, yellowish or purple, and its fruit is narrow and pod-like, in which bean seeds are located. Legumes are considered as the second source of human food after grains.