Effects of Mycorrhizal Symbiosis on Nutrient Uptake and Water Use Efficiency of Tomato under Drought Stress

Tomato is one of the most important vegetables that are used by human. High price of tomato due to its out of season production in Bushehr province has made a great tendency for farmers of this area to cultivate it in fall and winter in nearly 12000 hectares in the province. Mean annual precipitation is about 250 mm per year. Maximum and minimum annual temperatures are 51 and -1 Celsius degrees. Mean annual evaporation is 3000 mm. Recent droughts and going down of water table because of over usage of underground water are main problems of this region that have enforced farmers to decrease irrigation water utilization and try to increase water use efficiency by using new technologies. Therefore, any new technical methods which can increase water use efficiency will help crop production quality and quantity and result in yield stability in the region. Many researchers have proved that mycorrhizal fungi can improve agricultural systems sustainability because of their ability to increase water absorption due to their long and expanded hyphae. Also they are known to increase nutrient uptake from soils even poor in minerals. Therefore, a greenhouse project was designed to
determine the effect of Arbuscular mycorrhizal fungi on nutrients uptake and water use efficiency of tomato under drought stress in Bushehr province in southern Iran. The experiment was carried out on completely randomized block design in factorial with three replications during 2016-2017 in the greenhouse of Bushehr agricultural and natural resources research organization located in Southern Iran. Factors were as follows: 1) four Arbuscularmycorrhizal fungi (Glomus mosseae، Glomus intraradices ،Glomus vsersiform and Glomus caledonium) and a control (without inoculation), 2) irrigation at three levels based on soil moisture depletion at I1=25, I2=50 and I3=70 percent of available water to show stress (from non-stress to low and high stress levels). Soil used for this experiment was dried in sunshine for one month to be evacuated from any native fungi. Soils of the region are calcareous ones with low salinity limitation (EC= 3. 70 dS/m) and poor nutrition elements and slightly alkali (pH=7. 9). Inoculation of roots by fungi was done by pouring one spoon of fungi near tomato roots while cultivating the transported seedlings in the pot. This would help the roots to be exposed to fungi directly while spreading through growing. Irrigation water used were 22. 3, 20. 1 and 17. 7 liter for each pot filled with 10 kg soil during the season. The experiment lasted 100 days and tomato properties were measured such as yield,  colonization percent, nutrition elements concentration and also, water use efficiency. Dried leaves were milled and put in furnace at 550 Celsius degrees. Roots were soaked in water for five minutes to be detached from soil and cleaned toughly. Detached roots were maintained in small glass jars filled with alcohol and were kept inrefrigerator at 5 Celsius degrees. Roots were then colored by Try pan blue method and root colonization percent was measured by Grid line intersect method. Results showed that interaction effect of mycorrhizal fungi and irrigation levels was significant at 1% level on tomato properties (except for N concentration in leaves). Mean comparison with
Duncan`s test proved that increase in drought stress caused decrease in all tomato properties but fungi inoculation could mitigate water shortage in comparison to non-inoculated tomatoes Higher drought stress decreased colonization significantly. Drought stress caused significant deficiency in nutrition elements such as N, P and Fe, however some elements such as K, Zn and Mn were increased in medium drought stress.  Inoculation with all mycorrhizal fungi improved nutrition elements concentration in tomato leaves. Water use efficiency was increased 67. 9, 49. 6 and 52. 1 percent from non to medium and high stress respectively in tomatoes treated with Glomus intraradices. Using of mycorrhizal fungi specially Glomus intraradices and Glomus caledonium increased tomato water use efficiency and improved growth properties due to the increment of water resistance ability in plant. This phenomenon is caused by higher nutrition elements uptake by roots and optimization of water relationship in tomato in the presence of mycorrhizal fungi. According to results, it is suggested tomato roots inoculation with mycorrhizal fungi especially in regions with high water stress potential.