Arbuscular Mycorrhizal Responsiveness Of Wheat And Their Ancestors

Arbuscular mycorrhizal(AM)fungi can form mutualistic symbioses with the roots of wheat.Wheat supply AM fungi with carbohydrates,and in return,fungi increase nitrogen and phosphorus uptake of the wheat.Furthermore,AM fungi are able to enhance the tolerance of wheat against stresses of drought,cold and pathogens.The modern common wheat was originated from some ancestors such as Aegilops tauschii,Triticum urartu and other wild species.However,how these relative plants interact with AM fungi,how they respond to AM colonization,and whether soil nitrogen and phosphorus fertility will infulence these symbionts,are still pooly understood.To answer these questions,we investigated the AM responsiveness of wheat(Triticum aestivum)and their ancestors(Aegilops tauschii,Triticum urartu,Aegilops speltoides,Triticum turgidum)under different soil fertility conditions,using AM inoculation technique in a greenhouse.By analyzing the AM fungal colonization,plant biomass and other agronomic traits,we aimed to elucidate the symbiotic relationships between AM fungi and these plants,and to illustrate the AM responsiveness of these plants under different soil fertility conditions.Our research findings provide new insights in the understanding of the evolution of AM-dependency of modern wheat,and also facilitate the AM-based wheat breeding in future.The main results are as follows:(1)After mycorrhizal inoculation,all plant materials were colonized by AM fungi,but the effects of fertilization on AM fungal variables varied among different plant species.Fertilization significantly reduced the root length AM colonization in the root systems of Aegilops tauschii and Triticum aestivum,but it did not affect the AM colonization in the roots of Aegilops speltoides,Triticum Urartu and Triticum turgidum.Two-way ANOVA showed that fertilization and plant species had significant effects on the arbuscular colonization,vesicular colonization and spore density(all P < 0.03),and the arbuscular colonization,spore density and extraradical hyphal length density were affected by the interaction between fertilization and plant species(all P <0.01).(2)The biomass and nitrogen and phosphorus contents of different plant species were significantly affected by fertilization treatment.The total biomass and nitrogen content of most plant species were significantly increased by nitrogen fertilization and combined nitrogen and phosphorus fertilization.Inoculation with AM fungi significantly increased the total biomass of Aegilops speltoides and Aegilops tauschii,increased the phosphorus content of Aegilops tauschii,but decreased the phosphorus content of Triticum turgidum.Multi-way ANOVA showed that aboveground biomass,total biomass,root: shoot ratio,and nitrogen and phosphorus contents of plants were significantly affected by fertilization,plant species and their interaction(all P < 0.005).Mycorrhizal inoculation marginally affected the belowground biomass(P = 0.056)and plant phosphorus content(P = 0.05),but mycorrhizal inoculation and plant species had significant interactive effects on aboveground biomass,underground biomass,total biomass,root:shoot ratio and phosphorus content(all P < 0.03).In addition,mycorrhizal inoculation,plant species and fertilization had three-way interactive effects on nitrogen content(P = 0.049)and nitrogen: phosphorus ratio(P = 0.002).(3)The mycorrhizal response patterns of different plant species varied under each fertilization treatment.Under unfertilized condition,the mycorrhizal growth response(MGR)of Triticum turgidum was significantly negative(indicating that AM fungi suppressed plant growth),whereas the mycorrhizal nitrogen-uptake responses(MNR)of Aegilops tauschii and Aegilops speltoides were significantly positive(indicating that AM fungi promoted plant nitrogen uptake).Both MGR and MNR of Triticum aestivum were positive under nitrogen fertilization.Under phosphorus fertilization,both MGR and Phosphorus uptake response(MPR)of Triticum aestivum were negative,while the MGR of Aegilops speltoides was positive.Under combined nitrogen and phosphorus fertilization,the MGR,MNR and MPR of Aegilops tauschii were positive,but the MGR of Aegilops speltoides and MNR and MPR of Triticum turgidum were all negative.Cluster analysis showed that the mycorrhizal responsiveness of Triticum aestivum and Aegilops tauschii was closely related,suggesting that the genetic origin of mycorrhizal dependence of Triticum aestivum might be derived from Aegilops tauschii.In conclusion,this study shows that the relationships between wheat and its ancestor species with AM fungi were different,and that the effects of AM fungi on biomass and nutrient uptake of host plants were regulated by soil fertility.Our findings also suggest that the mycorrhizal dependence of current wheat might be genetically derived from Aegilops tauschii.The findings of this study will open up new ideas for the cross-studies of wheat breeding and symbiotic microorganisms,and will provide scientific supports for the wheat breeding with an AM symbiotic perspective.