| Citrus is the world’s number one fruit,but the citrus industry in many countries around the world has been hit hard by citrus Huanglongbing.There is no effective method to prevent and control citrus Huanglongbing.As the only natural vector for the spread of Huanglongbing-Diaphorina citri,the main means of its prevention is still mainly chemical control.Therefore,biological control has a significant potential for the control of citrus Huanglongbing and Diaphorina citri.Arbuscular Mycorrhizae(AM)fungi can form a good symbiosis with citrus.However,research on AM fungi has long been focused on promoting nutrient and water uptake,improving plant stress resistance and improving the inter-root environment,but research on pests and diseases is still lacking.Therefore,this paper investigates the effects of mycorrhizal fungi on the growth of citrus,resistance to Huanglongbing and interaction with Diaphorina citri to provide a theoretical basis for exploring new ways of citrus Huanglongbing and Diaphorina citri.The specific research results are as follows.(1)All the 9 AM fungis could form a good symbiotic relationship with citrus,and the infection rate of each treatment was higher than 80%.Nine AM fungi exhibited growth promoting and inhibition effects on C.junos.The score and ranking of each index(plant height,stem diameter,number of leaves,chlorophyll content,biomass,root activity,etc.)were calculated by membership function method.The results showed that 7AM fungis(R.c,P.s,R.i,R.s,G.v,C.t and A.k)had growth-promoting effects,and 2 AM fungis(C.l and C.s)had inhibitory effects.The best growth promoting effect was R.c(Rhizophagus clarus),whose plant height,stem diameter and number of leaves,chlorophyll content and biomass increased by 36.12%,21.24%,5.12%,17.47% and 70.52%,respectively.The mycorrhizal dependence reached 171%.(2)Citrus growth was inhibited to some extent under the stress of citrus Huanglongbing.However,inoculation of some AM fungis could alleviate the stress of Huanglongbing on citrus growth.Among them,R.i(Rhizophagus intraradices)could significantly promote the height and stem diameter of citrus under the stress of Huanglongbing,which were 49.7% and 35.6% higher than that of the control at 180 days after grafting,respectively.In addition,inoculation of some AM fungis reduced the content of huanglongbing in citrus leaves,and G.v(Glomus versiforme)showed the best performance.Inoculation of some AM fungis could significantly reduce the content of malondialdehyde(MDA)in leaves,and the best strain was G.v,which decreased by 37.28% compared with the control.The proline content in citrus leaves and roots increased by 90.25% in R.i.compared with the control.The SOD activity of citrus leaves and roots was significantly increased by C.t(Claroideoglomus tunicatum)and R.s(Rhizophagus sp.),which were 394% and 111%higher than that of the control,respectively.The POD activity in citrus leaves was significantly increased by R.C.(Rhizophagus Clarus),which increased by 49.73% compared with the control.The CAT content in citrus leaves and roots was significantly increased by 11.79% and 32.56%,respectively,compared with the control.(3)The infection rate and infection intensity of arbuscular mycorrhizal fungi in orange were decreased by Diaphorina citri The contents of endophytic bacteria Carsonella and Profftella in R.f.(Redeckera fulvum)were significantly lower than those in the control,and their relative expression levels were decreased by 56.1% and 53.6%,respectively.However,the content of Profftella was significantly lower in R.i(Rhizophagus intraradices)than in the control,and the relative expression of Profftella was reduced by 32.2% compared with the control.Inoculation treatment could reduce the survival rate of psyllid,among which,inoculation treatment R.f could significantly reduce the survival rate of psyllid at all stages,while inoculation treatment R.i could only significantly reduce the survival rate of psyllid at egg stage.Inoculation could significantly prolong the development duration of nymphs,and inoculation could significantly reduce the lifespan of adults by 10.15 days compared with control. |
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