Arbuscular Mycorrhizal Fungi(AMF) For Drought Tolerance Improvement In Maize(Zea Mays L.) And Tobacco(Nicotiana Tabacum L.)

Drought stress is the most significant crop limiting factor that results in severe yield reduction.It mostly affects the growth and development of plants by distressing ions uptake and enzymes activities,consequently decreases soil water potential thereby causes obstruction in water uptake by plant roots ultimately reducing the growth process.Drought exposure initiates several alterations in plant metabolism through increased generation of toxic molecules like reactive oxygen species(ROS).Hence,it is important to devise management strategies for improving the indigenous tolerance mechanisms for protecting growth and improving crop productivity in the changing environment.The Prime strategies include proper mineral fertilization or the use of beneficial microbes that directly or indirectly strengthen the tolerance mechanisms in plants.Among the beneficial soil microbes,arbuscular mycorrhizal fungi(AMF)is the main one that exist in the soil and have the ability to develop symbiotic association with nearly 90% of the plant species.The current research studies postulate that the AMF inoculation could be very useful agricultural practice that should be adopted in maize(Zea mays L.)and tobacco(Nicotiana tabacum L.)crops cultivation to moderate the damaging effects of drought and to sustain crop production in terms of yield and quality.To the best of our knowledge,little literature data is available concerning the interactive effects of drought stress and AMF inoculation on maize and tobacco crops cultivation in the arid or semiarid regions in northwest China.Hence the current research objective and focus was to study that;how arbuscular mycorrhizal fungus(Glomus versiforme))affects growth parameters,biochemical and agronomical traits of greenhouse grown maize(Zea mays L.)and tobacco(Nicotiana tabacum L)when treated with different level of drought stress.Moreover,we have studied the validation of(Glomus versiforme)in stress tolerance by developing several approaches,like analysis of growth traits and nutrient contents,photosynthetic alteration,up-regulating antioxidant system and plant growth hormones,osmolyte accumulation,secondary metabolites,essential oil content and chemical composition and glomalin content under drought stress conditions.The following are the obtained results.1.We have investigated the role of arbuscular mycorrhizal fungus(AMF,Glomus versiforme)in amelioration of drought-induced effects on growth and physiobiochemical attributes in maize.Maize plants were exposed to two drought regimes,i.e.,moderate drought(MD)and severe drought(SD),with and without AMF inoculation. Drought at both levels,MD and SD reduced plant height by 18.34% and 40.66% respectively,and chlorophyll by 54.67% and carotenoid content by 40.98%,thereby impeding photosynthesis.In addition,drought stress enhanced the generation of toxic reactive oxygen species(ROS),including H2O2 by 83.22% and 247.20% due to exposure to MD and SD,thereby resulting in enhancements of 92.94% and 206.32%,respectively,in lipid peroxidation,resulting in membrane damage reflected as increased electrolyte leakage and lipid peroxidation.Such negative effects were much more apparent under SD conditions that those of MD and the control.However,AMF inoculation significantly ameliorated the deleterious effects of drought-induced oxidative damage.Under control conditions,inoculation of AMF increased growth and photosynthesis by significantly improving chlorophyll content,mineral uptake and assimilation.AMF inoculation increased the content of compatible solutes,such as proline,free amino acids,glycine betaine and sugars by 69.84%,49.87%,107.14% and 142.8%,respectively,assisting in maintaining the relative water content.Up-regulation of the antioxidant system was obvious in AMF-inoculated plants,thereby mediating quick alleviation of oxidative effects of drought through elimination of ROS.2.Furthermore,Arbuscular mycorrhizal fungi(AMF)improved phosphorus(P)uptake in plants and regulate growth under stressed conditions.In this experiment we have examined the effect of phosphorus(P),40 mg kg-1 soil supplementation and AMF specie(Glomus versiforme)inoculation on the growth performance of tobacco under drought stress.Drought declined plant height by 42.95%,fresh weight by 21.66% and dry weight by 65% significantly.While Supplementation of P and inoculation of AMF significantly enhanced root colonization,growth,biomass accumulation and root activity of tobacco plants under drought stress conditions and alleviated the drought induced degeneration.Relative to drought stress plants,root colonization,plant height,fresh weight and dry weight accumulation and root activity increased by 64%,78%,377.71%,105.69% and 193.33%,147.53% in drought + AMF + P treated plants respectively.Also chlorophyll a,b,total chlorophylls and carotenoids by attained maximum increase of 93.40%,156.87%,92.99% and 76.21% respectively in AMF + P treated plants over control.Moreover,increased generation of reactive oxygen species(ROS)like hydrogen peroxide(H2O2)by 178.19% and superoxide(O2-)by 121.26% resulting in increased lipid peroxidation hence reducing membrane stability by 32.35%.Content of osmolytes includes proline,sugars and free amino acids increased by 23.77%,41.79% and 45.53% respectively due to AMF and P treatments under normal and drought conditions influencing the leaf relative water content.Relative to control,RWC increased by 23.60% in AMF + P and 62.96% in drought +AMF + P treated plants.Enhanced activities of SOD,POD,CAT,APX and GR was 105.50%,73.85%,83.56%,125.60% and 109.63% respectively were recorded due to AMF + P application under normal conditions.Drought stress resulted in enhancement of 28.41% for SOD,81.49% for POD,40.13% for CAT,23.67% for APX and 25.81% for GR over control plants,both at normal and drought conditions thereby ameliorating the oxidative effects.Further,accumulation of phenols(27.93%)increased more obviously due to P and/or AMF inoculation than in drought.Additionally Mycorrhizal inoculation along with P supplementation increased abscisic acid(ABA)by 87.44% in leaves and 168.80% in roots and indole-3-acetic acid(IAA)concentrations by 634.78% in leaves and 471% in roots under drought stress.3.In these trials we have further analyzed,the special effects of AMF and drought on the biochemical and morphological attributes of tobacco plant.It was observed that root colonization by AMF significantly increased with possible positive effects on biomass production and essential oil.The results indicated that drought at both levels affected the growth of tobacco by decreasing the plant height by 43.84% and 35.93%,and fresh(40.87%)and dry(49.76%)weight content therefore impeding the growth of tobacco.Nevertheless,inoculation of AMF considerably enhanced the harmful effects of drought-induced injury in tobacco plants.AMF inoculation improved plant height and fresh biomass under controlled conditions with significant uptake of mineral assimilation and thereby increasing secondary metabolites.The AMF inoculation significantly enhanced the yield,dry matter,oil fraction and the uptake of N,P and K with AMF in both drought and nondrought conditions.Although AMF inoculation considerably enhanced glomalin-related soil proteins with the percent increase of 50.80% for EE-GRSP,177.75% for DE-GRSP and 212.86% for TGRSP over control.Furthermore,accumulation of phenols and flavonoids were increased more obviously due to AMF inoculation rather than drought.Up-regulation of the lipexoygenase(LOX)by 90% and phenylalaninie ammonia lyase(PAL)by 125% was recorded.These enzymes were evident in the plants inoculated with AMF and thus arbitrating rapid possible mitigation of drought oxidative effects.Furthermore,AMF inoculation significantly improves the content and composition of essential oil.Overall 60,56,and 51 essential oil compounds were detected using GCMS from non AMF inoculated plants,while 82,82,and 80 compounds were observed from AMF inoculated plants respectively.Thus it was conclude that AMF modifies the tobacco plants secondary metabolism and approving the role of AMF symbiosis in plant defense against abiotic stresses.In conclusion,all these results signifying the positive role of arbuscular mycorrhizal fungi in plant growth and development.Usually AMF are also called as bio-fertilizers.In addition to this it is also accepted that AMF inoculation offers tolerance to the host plants against drought.The present study explained the role of arbuscular mycorrhizal fungus mainly(AMF,Glomus versiforme)in amelioration of drought-induced effects on growth and physio-biochemical attributes in maize(Zea mays L.),and Tobacco(Nicotiana tabacum L.).It is evident from the findings that the synergistic association of(Glomus versiforme)augmented host growth attributes and modulated physiochemical statuses under drought stress and consequently reduced oxidative damage and enhanced abiotic stress withstanding capabilities.These findings depicted that AMF modifies the plants growth and development thus approving the starring role of AMF symbiosis in plant defense against abiotic stresses.