The effect of symbiotic endophytic fungi in improving drought tolerance in tall fescue (Festuca arundinacea Schreb.)

Background and objectives
Endophytic fungi belong to the genus Epichloë (Neotyphodium=Acremonium), have a symbiotic relationship with many cool-season grasses. More than 100 species from 80 genera of the grass family, including tall fescue (Festuca arundinacea Schreb.), are known to be hosts of endophytic fungi. Endophytic fungi as biological agents alter vegetative, morphological and physiological traits of host plants, improve growth and increase their stability against biotic and abiotic stresses. In this research, the role of symbiotic endophyte fungi in increasing the tolerance of tall fescue against drought stress in hydroponic culture was investigated.
Materials and methods
In order to evaluate the role of Epichloë endophytic fungi in drought tolerance of tall fescue, the infected plants were identified by rose bengal staining method and microscopic observation. Endophyte-infected plant tillers were divided into two groups; one of which was treated with Fulicur and Propiconazol fungicides. After three months, the new tillers of the plants were examined after ensuring the removal of the endophyte fungus from the treated plants; the new tillers were propagated from endophyte-infected and endophyte-free clones. Then they transferred to Johnson’s nutrient solutions with half concentration. Drought stress was applied by adding polyethylene glycol 6000 (PEG-6000) to the nutrient solution. Drought stress treatments included the control treatment with zero osmotic potential and the others with -3, -6 and -8 Bar, osmotic potentials. The factorial experiment was done using a completely randomized design with six replications. The first factor was the presence and absence of endophyte fungi in two levels and the second factor was drought stress in five levels. Data were collected for tiller number, shoot weight, root weight, crown weight, and biomass weight per plant.
Results
The results of variance analysis showed the significant effect of endophyte fungus on all traits except leaf length (P<0.01), as well as the significant effect of drought treatments on all traits (P<0.01). The endophyte fungus by drought stress was significant for root length (P<0.05), aerial fresh weight and crown weight (P<0.05). The result of mean comparison showed that in most of the studied traits, such as tiller numbers and root and crown weight, the endophyte-infected plants had higher mean values than that for endophyte-free plants. The mean comparing between endophyte infected and free fungi plants showed that the number of tillers in endophyte-infected plants was 15.12 and in endophyte-free plants, it was 5.95, which indicates a 3-times increase in the number of tillers in endophyte-infected plants. The mean comparison in different drought treatments showed that the increase in drought stress caused a significant decrease in most traits. For example, the highest tiller number with a value of 17.25 was observed in the control, but it decreased to 8.66 tillers per plant in the -8 Bar treatment. The root weight was strongly affected by drought stress and its value was 14.44 g/plant in the control treatment, and it decreased to 3.80 g/plant in drought stress of the -8 Bar treatment. The result of endophyte fungus by drought stress interaction showed that the difference between treatments was more noticeable in high stresses. For example, the root weight in the endophyte-infected plants has decreased from 5.08 to 2.52 g/plant in endophyte-free plants in -8 Bar drought stress.
Conclusion
The results of this research showed that the native endophytic fungi play an effective role in the improvement of host plant tolerance against drought stress. Therefore, in such conditions of climate change, where drought stress is one of its main problems, the use of symbiotic endophytes of plants could be one of the effective factors in facing climate change.