Effects Of Meloidogyne Incognita On The Relationship Among Wheat,Sitobion Avenae And The Natural Enenmy

In the agricultural ecosystem,crops are often harmed by pests above ground and below ground.As an organic whole,plants are often induced to produce some resistant substances when they are damaged by above ground diseases and insect pests.These substances can directly or indirectly affect the behavioral response of aboveground herbivores and their natural enemies.At present,plant defense single damage of aphid and nematode has been reported.However,it is not clear how plants respond to aphid and nematode attacks at the same time.In addition,there are few studies on the effects of wheat aphids on the natural enemies after feeding on wheat.Thus,our study investigated the effects of Meloidogyne incognita in different densities on the feeding and selection behavior of above ground pest Sitobion avenae(Fabricius)on wheat in different time periods,and the effects on host location of Harmonia axyridis.We also analysis volatiles,hormones and photosynthesis of wheat after attack.We investigated the changes of growth and defense strategies of wheat under the successive invasion and simultaneous damage of different pests were revealed.Our study provides theoretical support for the rational utilization of natural enemies when multiple diseases and pests cross harm,and to provide new ideas for elucidating the mechanism of wheat induced resistance and wheat pest control.The main findings are as follows:1.Effects of Meloidogyne incognita on the behavior of Sitobion avenae(Fabricius)and Harmonia axyridisThe behavioral responses of aphids and its natural enemy H.axyridis to wheat were measured by Y-olfactometer.The results showed that the effects of M.incognita infection on host location of aphids and its natural enemy H.axyridis were related to the density of nematodes and the duration of damage.When nematode density was low(300 heads / plant),M.incognita infection had no effect on the behavior of aphids;when the density of nematodes reached 500 heads / plant,the aphid tended to choose healthy wheat,but with the increase of time,the selection difference decreased;when the nematode density reached 1000 heads / plant,the M.incognita was found at 3 and 5 days of infection.However,with the extension of infection time,aphid tended to choose wheat infected by M.incognita at 7 days.The results showed that the behavior of H.axyridis was similar to that of aphids after root knot nematode infestation.When the density of nematode was lower(300 heads / plant),it did not affect the behavior of H.axyridis;when the density of nematode reached 500 individuals / plant,the behavior of H.axyridis was different only after 5 days of infection,and the H.axyridis tended to choose healthy wheat plants When the degree of infection reached 1000 head / seed,the selection behavior of the aphid was the same as that of aphids.The results showed that there was no significant difference between the three inoculated amounts of M.incognita on the three-and five-day wheat infected by M.incognita,and the H.axyridis to choose the plant of M.incognita after 7 days of the damage.The feeding behavior of aphids was measured by EPG.The results showed that the feeding behavior of aphids was inhibited to a certain extent by nematode infestation,mainly in the following aspects: the duration of non-probing wave(NP wave)increased,the duration of path wave(C wave)increased,and the feeding wave(E2 wave)time decreased;however,with the increase of nematode density and the increase of damage time,the inhibition effect gradually decreased.The inhibitory effect of M.incognita on the feeding of aphids disappeared.2.Effects of M.incognita and S.avenae(F.)on volatiles of wheatPermanova and PCo A were used to analyze the volatiles of M.incognita.The results showed that the species of wheat volatiles did not change at different time points and nematode density,but mainly affected the contents of volatiles.The differences of volatiles under different densities varied with time.There were significant differences in the volatiles of uninfected wheat,300 nematodes,500 nematodes and 1000 nematodes at 3d and 7d,but significant differences were found among the treatments at 5d.In the presence of aphids,M.incognita infection did not affect the species of wheat volatiles,which similar to the single infection of M.incognita.In the presence of aphids,the effect of M.incognita on volatiles was mainly at 3d and 7d,but there was no significant difference between the densities at 5d.3.Effects of M.incognita and S.avenae(F.)on hormone and photosynthesis in wheatThe contents of salicylic acid and jasmonic acid in the aerial and underground parts of wheat were determined by LC-MS.The results showed that the relative content of JA in roots decreased when the number of nematodes was less and the infection time was shorter,while the SA content decreased first and then increased.However,with the extension of the infection time and the increase of the number of nematodes,the content of JA in roots increased significantly,while the content of SA decreased significantly.At the initial stage of infection,the relative content of JA in wheat leaves increased significantly,but the change of SA content was not affected.Compared with aphid infection alone,the change of leaf hormone was related to the density and infection time of nematode.When the nematode concentration was low,the SA content in leaves decreased significantly,but with the increase of infection time,the SA content increased significantly,and the change of JA content was consistent with that of aphids feeding alone.The photosynthesis of wheat was measured by photosynthesis instrument.The results showed that both M.incognita and / or aphids caused significant increase in photosynthesis of wheat,but the effect of nematodes on plant photosynthesis was small and increased with the increase of nematode damage time and density.