The Response Of Arbuscular Mycorrhiza To Low PH And The Regulation Pattern Of Phytohormones

Acidic red soils in South China account for nearly 1/3 of Chinese terrestrial area and is an important resource with abundant hydro-thermal resources and high potential of agricultural production.However,due to the constraints of low p H and other factors,the potential of crop root growth,nutrient absorption,yield and quality are suppressed.The main utilization way of acidic soil in South China is orchard.At present,many orchards in South China are facing acidic stress.Arbuscular mycorrhizal（AM）fungi is a type of soil fungus that can establish symbiosis with plants.AM fungi can survive in many types of soil,are widely distributed in nature,and can effectively improve the resistance of plants to low p H,thereby promoting the growth of plants and improving acidic soil.The core functional structure of AM symbiont is arbuscule,but the response pattern of AM development and function to low p H is still unclear.Recent studies have shown that phytohormones,as an important signaling substance,can regulate the symbiosis of plants and AM fungi,but it is unclear whether phytohormones regulate the development and function of arbuscule under low p H.It is of great significance to study the effect and the regulation of phytohormones on AM development and function under low p H conditions,which is important to the agricultural production in the acidic red soil in South China.It can not only improve the production potential of crops in this region by regulating the development and function of AM,but also enrich the research of mycorrhizal biology and soil ecology.It is of great significance to study the effect and the regulation of phytohormones on AM development and function under low p H conditions,which is important to the agricultural production in the acidic red soil in south China.In this study,the model plant tomato（Solanum lycopersicum）was used as the host plant,inoculated with AM fungi,using different tomato phytohormone mutants,and using a sterile culture system to study how low p H affects the development and function of AM;response pattern of phytohormones in mycorrhiza under low p H conditions;how different hormones（IAA,ABA,GA）regulate the development and function of AM under low p H conditions.This study obtained the following results:（1）The results of the pot experiment showed that the acidic soil reduced the plant biomass,and the mycorrhizal colonization in the acidic soil was significantly reduced.Acidic soil strongly inhibited the function of AM fungi by inhibiting the formation of arbuscule.（2）The experiments with hairy root aseptic culture system showed that the low p H in this study had no significant effect on the root biomass either the phytohormone mutants or their corresponding wild-type tomato cultivars,but significantly inhibited the root biomass of’Xinjinfeng No.1’.（3）The effect of low p H on the mycorrhizal colonization of different cultivars of tomato is different,but low p H inhibited the development of arbuscules and thus affected the function of AM.Arbuscular structure normally formed under low p H conditions with hairy root aseptic culture system,which was different from the results in acidic soil,therefor,the inhibition of arbuscule development in acidic soil may be caused by other factors.（4）Inoculation with AM fungi can caused changes in the content of different phytohormones in plants,but these changes generally occurred in the early and middle stages,and the impact was small in the later stages.（5）ABA at a suitable content(10^-7M)promoted the formation and function of arbuscules.The inhibition of mycorrhizal colonization and arbuscular abundance at low p H might be achieved by reducing the content of ABA in plants.GA strongly inhibited mycorrhizal colonization and the formation and function of arbuscules.Exogenous gibberellin treatment inhibited endogenous GA biosynthesis in plants.IAA can promote mycorrhizal colonization,but it needs a suitable content and different cultivars have different suitable content.（6）Rhizophagus irregularis DAOM 197198 produced spores in asymbiotic status;ABA could directly act on spores,significantly promoting the spore production in both symbiotic and pre-symbiotic status;volatile root exudates significantly promoted the spore production of R.irregularis DAOM 197198 in pre-symbiotic status.The diameter of the newly produced spores in the symbiotic and pre-symbiotic status was smaller than that of the mother spores,which was about half the diameter of the spores produced under symbiotic conditions.This study is of great significance to achieve the pure culture of AM fungi.