Effects Of Endophyte Piriformospora Indica On Salt And Drought Tolerance Of Brassica Napus

Food shortage remains a great concern with the increasing population,yet crop production is facing threats from multiple environmental stresses under climate change.Various techniques have been explored to increase crop resistance under stress to secure crop production.Biotechnique,which utilizes plant-microbe symbiosis,is considered an efficient and eco-friendly approach with great potential to improve crop production.Piriformospora indica is an endophytic fungus,a model organism of Sebacinales family.P.indica has distinguished itself because of its large spectrum of host plants and axenic culturable nature.Root colonization by P.indica promotes growth,increases yield,and enhances stress resistance of the host plants.Brassica napus,also known as canola or rapeseed,is an economically important oil crop cultivated worldwide.Earlier studies identified B.napus as an ideal host for P.indica.In this research,the physiological and growth responses of B.napus were examined in the greenhouse experiments to determine the effectiveness of P.indica in improving growth characteristics and stress resistance of B.napus plants.The research has extended our knowledge of the practical application of P.indica in crop agriculture.The main conclusions are as follows:1)I explored different in-vitro culture methods of P.indica and selected optimum protocols for inoculating B.napus roots with this fungus.Five synthetic solid(with agar)and liquid(with liquid)media(PDA,MS,AMM,KM,and MMN)and four different inoculation strategies were tested.The results indicated that KM medium,both in agar and liquid,was the best media for cultivating P.indica.The most successful root colonization was found when P.indica and seedlings of B.napus co-cultivated in the MS medium,which reached about 52%root colonization rate.In addition,P.indica on plant growth was studied on different inoculation days.Three days after inoculation,P.indica significantly increased leaf chlorophyll concentration in plants.P.indica impacted B.napus growth seven days after inoculation.The difference remained after the seedlings were transferred to the soil substrate.2)To test the impacts of P.indica colonization on B.napus under salt stress,physiological and molecular parameters of plants were determined under different concentrations of NaCl(0,100,200,300,and 400 mM).The results demonstrated that the presence of P.indica alleviated the adverse effects of salt stress.Inoculated plants showed significantly higher shoot heights,stem diameters,and biomass accumulation than non-inoculated B.napus.Under salt treatment,leaf gas exchange,leaf chlorophyll fluorescence,and leaf water content decreased.Additionally,inoculation treatment significantly increased stomatal conductance in plants treated with 100 mM NaCl.At 200 mM NaCl,inoculation significantly increased shoot nitrogen content and root phosphorus content at 400 mM NaCl.Na+concentrations increased in the NaCl-treated plants.While shoot K+,Ca2+,and Mg2+decreased with NaCl,root K+and Mg2+did not differ among NaCl levels,and Ca2+ concentrations decreased significantly.Expression of plasma membrane intrinsic proteins(PIPs)of root was significantly affected by salt stress.Inoculation treatment significantly up-regulated the relative expression levels of BnPIPl;1,and downregulated BnPIP2;5.3)Drought stress(severe drought-30%soil water content,mild drought-60%soil water content,and non-droughted control-90%soil water content)was imposed for 14 days.The growth and physiological parameters of inoculated and non-inoculated seedlings were examined.The results showed that drought stress negatively affected plant growth,especially under severe drought conditions.Drought stress reduced shoot and root biomass as well as the specific leaf area.However,P.indica inoculation relieved the adverse effects of drought.Furthermore,drought reduced leaf transpiration rates,stomatal conductance,and intercellular CO2 concentrations,while these parameters were higher in the inoculated group under stress conditions.Compared with non-drought control,severe drought decreased relative water content and leaf water potential in non-inoculated plants,while inoculated plants did not change under drought.In conclusion,the thesis research successfully determined an optimal medium for P.indica cultivation and a stable symbiotic system for P.indica and B.napus was achieved.The results demonstrated the growth-promoting and stress resistance-enhancing effects of canola root colonization by P.indica.The physiological mechanisms of P.indica promoting salt and drought tolerance in B.napus was elucidated.The findings provide insight into plant-microbe interactions under environmental stress,which may serve as theoretical references for utilizing P.indica colonization to increase crop production in China.