Effects Of Wheat Infected With Powdery Mildew (Blumeria Graminisf) On Winter Wheat, Aphid (Sitobion Avenae) And Parasitoid (Aphidius Gifuensis)

The English grain aphid Sitobion avenae(Fabricius) is a major pest of wheat in the world, which causes huge loss every year. The aphid usually occurs together with the powdery mildew(Blumeria graminisf(DC.) Speer)) on wheat under field conditions.Evidences are presented that show the pathogen infection can affect the herbivore which range from positive to negative directly or indirectly on tri- or tetra-trophic interactions. In this study, we conducted a series of experiments(Wheat-Health or H, Wheat-Fungicide or F,Wheat-Powdery Mildew or PM, Wheat-Powdery mildew-Fungicide or PM-F) to explore the effect of plant pathogens(B. graminisf) on the herbivores(S. avenae) on the multritrophic level interactions(pathogen, fungicide, plant, herbivore and natural enemies). The effects of the plant defensive system on the aphid and powdery mildew were also investigated from the perspective of the host plant induced resistance, nutrition and natural enemies(Aphidius gifuensis). The results were as follows:1. S. avenae performance on four pre-treatment(H/F/PM/PM-F) wheat. The results showed that negative fitness consequences for the aphid when feeding on the wheat leaves infected by the powdery mildew. Performance parameters were generally worse on PM treatment compared to H and F treatments. The PM-F treatment followed the trend but the daily fecundity of it significantly increased with time compared with M treatment.2. Aphid probing behavior on four pre-treatment(H/F/PM/PM-F) wheat. Electrical penetration graph(EPG) recordings of aphid probing behavior revealed that nine EPG parameters were significantly different when the plant penetration behavior of S. avenae was monitored on four treated wheat leaves, and the total duration of phloem ingestion significantly decreased and xylem ingestion occurred more often and prolonged on PM and PM-F treated wheat leaves in comparison with the two other treatments. These findings suggest that powdery mildew infection may induce feeding detergents in wheat mesophyll.3. Effects on nutritional status of host plants. The amino acid and soluble sugar concentrations were analyzed using LC-MS. The results showed that the contents of the total amino acids and soluble sugars were significantly decreased with time except that the totalamino acids of the PM treated leaves were significantly increased with time. On day 25, the levels of sucrose, melezitose and trehalose significantly increased in the PM treated wheat relative to the H and F treated wheat but the ratio of essential amino acid to amino acids in wheat leaf phloem exudates significantly decreased. The ratio of essential amino acid to amino acids in the PM-F treated wheat significantly decreased on day 19 but not on day 25.Among the 19 amino acids detected, the levels of Pro and Gln in the PM and PM-F treated leaves were significantly higher than those in the H and F treatments. Our results suggest that powdery mildew infection can change the content and balance of host plant nutrition, which,in turn, influence the development of S. avenae.4. The content of secondary substances and defense enzyme activity in the four treated wheat leaves. The PM treated wheat leaves extract contained the highest total phenolic on day3, followed by the PM-F treated leaves extracts. The antioxidant enzymes(T-SOD, POD,CAT) were also higher in the PM and PM-F treatments than in the H and F treatments, except T-SOD on day 25. These findings suggest that powdery mildew infection may induce a series of physiological and biochemical changes in wheat, including secondary substances and defense enzyme, which can enhance the resistance to the latter host.5. The influences of powdery mildew induced wheat plant volatile compounds on the olfactory responses of aphid parasitoid(A. gufiensis) were examined in two-choice tests using a Y-tube olfactometer. In the Y-tube choice experiment, the wasp preference significantly varied among the treatments. When the tested wheat were infested with aphids, significantly more parasitic wasps were attracted to the volatiles from the PM and PM-F treated wheat leaves over the volatiles from the H and F treated wheat.Collectively, our results suggest that the B. graminisf can have a negative effect on the S.avenae by altering the food and refuge qualities of the host plant, and controlling powdery mildew using fungicide will be beneficial to control the English grain aphids in wheat.