Constitutive And Induced Defenses Of Wheat Against Sitobion Avenae

The English grain aphid Sitobion avenae is a major pest of wheat. In this study, weexamined antibiosis and growth tolerance of some wheat cultivars to S. avenae and evaluatedsome chemical activators on wheat defenses against this aphid. First, we found that the wheatcultivar XY22had better antibiosis and growth tolerance to S. avenae. Sitobion avenae didnot show any preference to the wheat cultivars tested. The electrical penetration graph (EPG)data indicated that the resistance factor of XY22is phloem-located. Aphids feeding on XY22had significantly lower mean and total phloem ingestion periods compared with those feedingon other wheat cultivars, which suggests that there are feeding deterrents in phloem of XY22or XY22has stronger and faster phloem occlusion responses when challenged by aphid injury.However, changes of wheat polyphenol oxidase and peroxidase activities as well as plantphotosynthetic rates are not consistent with plant resistance to S. avenae. These resultssuggest that XY22may achieve antibiosis and growth tolerance to S. avenae by limitingaphid feeding. Exogenously applied plant defense signals jasmonate and salicylate on wheatseedlings had no significant effects on performance of S. avenae. Sitobion avenae prefercontrol wheat seedlings compared with jasmonate-or salicylate-treated plants. EPG resultsindicated that S. avenae had more probes on jasmonate-treated plants and the duration of firstprobe was significantly shorter compared with those on control plants. The mean phloemingestion period of S. avenae on SA-treated plants decreased significantly, while salivationtime increased significantly. These findings suggest that jasmonate may induce feedingdetergents in wheat mesophyll, while salicylate possibly primed wheat phloem occulusionresponses. Wheat seedlings root-drenched with beta-aminobutyric acid significantly reducedweight of S. avenae and the effect was dose-dependemt. However, beta-aminobutyric acidtreatment had no impacts on aphid host preference and feeding activities, suggesting thatbeta-aminobutyric acid did not induce repellent or antifeedent in wheat seedlings. Theconcentration of beta-aminobutyric acid in beta-aminobutyric acid-treated plants wassignificantly higher than that in control treated plants and the high level beta-aminobutyricacid concentration maintained at least for10days, which suggests that wheat seedlings canuptake beta-aminobutyric acid quickly but decompose it slowly. Using artificial diet, wefound that beta-aminobutyric acid had direct toxic effects on S. avenae. Aphid weight was significantly lower when reared on artificial diet containing beta-aminobutyric acid. Insummary, we investigated constitutive and induced wheat resistance to S. avenae and foundthat XY22realized better antibiosis and growth tolerance to S. avenae by limiting aphidfeeding; jasmonate and salicylate application on wheat had marginal impacts on S. avenaeperformance, but significantly reduced host preference of this aphid;beta-aminobutyric-mediated wheat resistance to S. avenae was possibly due to its directtoxicity on aphids. These results broad our understanding of mechanism of plant resistance toaphids and provide new insights in pest management.