Effect Of Arbuscular Mycorrhizal Fungi On Growth And Drought Resistance Of Pear Seedlings Under Water Stress

With the development of science and technology,drought is still one of the main natural disasters facing mankind.It has high frequency,long duration and wide influence range,which seriously affects the growth,development and reproduction of plants.In recent years,the fruit industry has developed rapidly,and water is one of the important factors affecting the quality and yield of fruit trees.Pear tree is one of the most important economic planting fruit trees in north and south of China.At present,the natural precipitation and artificial irrigation in many pear producing areas in China can not meet the needs of pear tree growth.Arbuscular mycorrhizal fungi（arbuscular mycorrhizal fungi,AMF）can form mycorrhizal symbiotic relationship with most higher plants and improve plant drought resistance.Although many studies have shown that AMF plays a certain role in plant drought resistance,there are few studies on the effects of AMF on the growth and drought resistance of pear trees under different degrees of drought stress,so it is necessary to study this.This experiment selected Funneliformis mosseae（recorded as:F.m）and Glo mus etunicatum（recorded as:G.e）as test bacteria.Potted―Cuiyu‖pear saplings（Pyrus.pyrofolia cv.cuiyu.）were used as test materials,different water treatment s of pear seedlings by artificial drought simulation,A total of 12 treatments we re set up in the test:（1）well watered and non-mycorrhizal（WW-NAM）,（2）we ll watered and F.m（WW-F.m）,（3）well watered and G.e（WW-G.e）,（4）Light drought and non-mycorrhizal（LD-NAM）,（5）Light drought and F.m（LD-F.m）,（6）Light drought and G.e（LD-G.e）,（7）Moderate drought and non-mycorrhizal（MD-NAM）,（8）Moderate drought and F.m（MD-F.m）,（9）Moderate drought and G.e（MD-G.e）,（10）Severe drought and non-mycorrhizal（SD-NAM）,（11）Seve re drought and F.m（SD-F.m）,（12）Severe drought and G.e（SD-G.e）.Effects of the two AMF on leaf and root growth,antioxidant enzyme activity,endogenou s hormones and relative expression of drought-resistant genes were studied.The results of this experiment are as follows:1.Infection rate of AMF was 51.44%and 61.21%under different water treatment.The results showed that F.m and G.e could infect the root system of pear seedlings.At the same time,the mycorrhizal dependence of pear seedlings increased with the strengthening of drought stress,and the mycorrhizal dependence reached the maximum under severe drought conditions,and the effect of G.e was better.2.Two AMF promote the vegetative growth of pear seedlings.F.m and G.e can increase the plant height,stem diameter,leaf area,chlorophyll content,relative water content and net photosynthetic rate of pear seedlings to varying degrees,and promote the growth of pear seedlings and alleviate the damage to pear seedlings caused by different degrees of drought stress.AMF also promoted the root development of pear seedlings.The root activity,root volume,longest lateral root number,number of new roots in the AMF group and the ratio of root to crown were higher than those in the NAM group.AMF improved the root morphology,promoted the root system to absorb more water and nutrients,and improved the drought resistance of pear seedlings.3.At different experimental stages and under different drought stress levels,both AMF play different roles in osmotic regulation and antioxidant capacity of pear seedlings,both AMF promote the accumulation of soluble sugar,soluble protein and free proline,the contents of malondialdehyde（MDA）and hydrogen peroxide（H₂O₂）were decreased,The activities of superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）,ascorbate peroxidase（APX）were improved.As the degree of drought increases,AMF benefits are becoming more significant,AMF under moderate and severe drought stress at each trial stage was the best.Overall G.e is better than F.m.4.Under different degrees of drought,both AMF promoted the accumulation of endogenous auxin（IAA）,erythromycin（GAs）,jasmonic acid（JA）and brassinosterol（BR）in the roots and leaves of pear seedlings.As the degree of drought increased,the efficiency of mycorrhizae became more and more significant,and the AMF effect was better under moderate and severe drought stress.Both AMF regulate the balance between various hormones,coordinate and interact with each other,and improve the drought resistance of pear seedlings.5.The expression level of Pb ARF2、Pb ARF7 gene increased in leaves and roots of pear seedlings with the increase of drought stress,AMF group was higher than that of NAM group.The relative expression of Pb ARF2 was highest under moderate drought conditions and the Pb ARF7 was the highest under severe drought.Overall,mycorrhizal benefit is higher than leaf in root system,mycorrhizal benefit is the highest under severe drought condition,and G.e effect is better than F.m.effect.The two AMF induced the expression of Pb ARF2、Pb ARF7 two genes,improved the drought resistance of pear seedlings and adapted to different degrees of drought environment.To sum up,under different degrees of drought,the two AMF promoted the vegetative growth of pear seedlings,improve the osmotic regulation and antioxidant ability of pear seedlings,regulate the balance of endogenous hormones of various plants,and induce the expression Pb ARF2、Pb ARF7 drought resistance genes.The drought resistance of pear seedlings was improved.