Establishment Of Symbiotic System Of Piriformospora Indica And Rhododendron And Its Effect On Improving Drought Resistance

Rhododendron is a common shrub species in urban landscaping in southern China.With the intensification of global warming,drought and other disastrous weather occur frequently.In the months of high temperature or drought in summer,most Rhododendron will show different degrees of wilting and even death,which seriously restricts the application of Rhododendron in urban garden green space.In this study,the co-culture system of Piriformospora indicaRhododendron was established by using Rhododendron pulchrum,which is widely used in urban garden green space.The morphological structure and physiological and biochemical changes of Rhododendron plants colonized with Piriformospora indica were preliminarily explored.The effect of Piriformospora indica on the drought resistance of Rhododendron and the changes of some related physiological and biochemical indexes were explored.The main results are summarized as follows:1.Piriformospora indica can establish symbiotic relationship with Rhododendron.Piriformospora indica chlamydospores began to colonize in the roots of Rhododendron after 4 times of irrigation.The colonization rate reached 91.67 % after 5 times of irrigation and reached 100 % after 6times of irrigation.Through colonization identification,it was found that only chlamydospores of Piriformospora indica could be observed in the roots of plants,and no hyphae were found.2.Colonization of Piriformospora indica had significant effects on the morphology,physiology and biochemistry of Rhododendron plants.After Piriformospora indica colonized in the roots of Rhododendron for 30 days,the fresh weight,dry weight and leaf area of Rhododendron leaves increased,the tightness of leaf structure increased,the ability of stomata to pass gas increased,and the contents of auxin and abscisic acid in leaves increased.The area of root cells increased,the contents of auxin,abscisic acid and salicylic acid in roots increased,and the content of zeatin decreased.3.It is clear that Piriformospora indica can improve the drought resistance of Rhododendron.Through gradient water control to simulate drought stress,it was found that the root cell structure of Rhododendron colonized by Piriformospora indica was more stable.Compared with the phenomenon of cell membrane rupture and organelle degradation of uncolonized roots,the plants colonized by Piriformospora indica could ensure the integrity of cell membrane,mitochondria,and other cell structures.Then,the watering was stopped after sufficient watering,and the drought stress was simulated for 20 days when the relative water content of the soil decreased to the stress level.It was found that the leaves of the uncolonized Piriformospora indica began to wilt at 0 d.With the prolongation of drought stress time,the wilting degree of the leaves of the uncolonized Piriformospora indica deepened,withered,and even fell off.The azaleas colonized by Piriformospora indica wilted after 5 days,and the degree of stress was lighter with the prolongation of stress time.After20 days of stress,the mortality rate of non-colonized Rhododendron was as high as 52.33 %,and that of colonized Rhododendron was 6.67 %.According to the Logistic equation combined with the relative conductivity,the LT50 was fitted.The LT50 of Rhododendron colonized by Piriformospora indica was 41.32 d,which was significantly longer than8.49 d of non-colonized Rhododendron.4.Physiological response of colonization of Piriformospora indica under drought stress.Through two methods to simulate drought stress,it was found that the damage degree of cell membrane of Rhododendron colonized by Piriformospora indica was reduced,which was mainly reflected in the lower relative conductivity and malondialdehyde content than that of uncolonized Rhododendron.Compared with the increase of light and pigment content,the decrease of SOD activity and the accumulation of proline content in non-colonized Rhododendron under drought stress,the internal physiological and biochemical indexes of Rhododendron colonized with Piriformospora indica a under drought stress fluctuated little and had strong stability.