Study On The Effect Of Endophytic Fungi From Hemp On The Salt Tolerance Of Hemp (Cannabis Sativa L.)

Salt stress severely inhibits plant growth and soil salinization is becoming more and more serious.Although several methods have been developed to enhance plant tolerance to soil salinity,these methods have shortcomings.Some endophytic fungi can not only increase the absorption of nutrients by plants and induce plant resistance to salt stress when symbiotic with plants,but also improve soil conditions by changing the composition of microbial communities in the soil.In the present study,potentially salt-tolerant endophytic fungi were isolated from hemp plants of different cutivars that were grown under salt-stressed condition.Subsequent experiments shown that a few of the isolated endophytic fungi can increase tolerance of the tested hemp cultivars to salinity.(1)Industrial hemp cultivars BM and Y5 were used as research materials.Endophytic fungiwere isolated and purifiedusing traditional methods from hemp plants growing under different NaCl concentrations(0,100,200,300 mmol/L).The obtained fungi were subsequently identified though their morphology and rDNA-ITS sequence.A total of 442 fungal strains were isolated from 1400 hemp tissue slices of BM,belonging to 14 families,18 genera,and 43 species.543 fungal strains were isolated from 1400 hemp tissue slices of Y5,belonging to 21 families,26 genera,43 species.In all the treatments,species closely related to stress resistance,Chaetomium globosum,Trichoderma harzianum,Cladosporium sp.,Annalohypoxylon stygium,etc.,were isolated.(2)It was found that the growth of hemp seedlings was mildly inhibited when grown on medium with 100 mmol/L NaCl while the inhibition was severe on medium with 200 mmol/L NaCl.On medium with 300 mmol/L NaCl,the seedlings stopped growth and developed chlosis.Thus,medium with 200 mmol/L NaCl was used to cultivate sterile hemp seedlings.After 2 weeks of growth,the seedlings were inoculated with Chaetomium globosum,Trichoderma harzianum,Cladosporium sp,Annalohypoxylon stygium.3 weeks after inoculation,it was found that the inoculated 4 species of endophytic fungi in symbiosis with hemp.(3)Chaetomium globosum,Trichoderma harzianum and Annalohypoxylon stygium were back inoculated to salt tolerant hemp cultivar BM and salt sensitive cultivar Y6 to verify if they can improve salt tolerance of hemp.The results showed that the inoculation reduced the content of proline and malonaldehyde,decreased the electric conductivity and the content of soluble sugar,increased the activity of SOD and POD,and increased soluble proteinand chlorophyll under salt stress.In all the stress levels,the inoculation of three fungi significantly increased the stem thickness,leaf water content,dry weight,plant height,and fresh weight of BM.However,the promotion effect of Y6 stem thickness,plant height and leaf moisture content was limited.(4)The principal component analysis method was used to analyze the effects of 14 growth and physiological indicators of cannabis on the salt tolerance of industrial hemp and a comprehensive evaluation.This study showed that stem thickness,dry weight,fresh weight,chlorophyll content of hemp could be used as the primary evaluation indicators for the endophytic fungi in alleviation of salt stress of hemp.According to the ranking of comprehensive principal component,hemp cultivar Y6 showed a larger mitigation effect against salt stress than BM after inoculated the three endophytic fungi.The ranking of the three endophytic fungi in promotion of hemp growth was Trichoderma harzianum >Annalohypoxylon stygium > Chaetomium globosum while the ranking in alleviation of salt stress was Chaetomium globosum > Annalohypoxylon stygium > Trichoderma harzianum.In summary,some endophytic fungi participated in the adaptation process of hemp under salt stress that enhanced the tolerance of hemp to the stress,but the effect of different endophytic fungi and the response of different hemp cultivars to these endophytic fungi were different.