Abstract The greenbug (Schizaphis graminum Rondani) is one of the most destructive cereal aphids worldwide, which feeds on phloem sap and has the ability of transmitting plant viruses. Greenbug feeding can induce leaf chlorosis, reduction of plant quality and even plant death. Considering the effect of herbivores on plant defense system, the plant pre-infestation with aphids can affect their subsequent populations. Pre-infestation could either induce resistance in plants by activating defense system or increase pests’ performance by local defense suppression. Temperature is an important environmental factor which affects insects, including aphids, as poikilothermic organisms. Temperature change affects insects not only directly via insects’ biology but also indirectly by altering the nutritional quality of host plant. The aim of this study was to investigate the effect of temperature (21 and 25º C) and feeding duration of S. graminum (24, 48 and 72 hours) on antioxidant defense related biochemical parameters in wheat plant. To achieve this goal, the content of hydrogen peroxide (H2O2), malondialdehyde (MDA) and the antioxidant enzyme activity of catalase (CAT), guaiacol peroxidase (GPX) and glutathione S-transferases (GST) were measured in wheat leaves. Also, the effect of two different densities of previous infestation (5 and 10 aphids per plant) on some life table parameters of S. graminum was eva‎luated. Assessment of life table parameters showed that nymphal period of S. graminum was significantly reduced in pre-infested plants (both densities) compared to control. An increase in the adult longevity of S. graminum was observed in 10-aphid pre-infested plants compared to control. Previous infestation caused a significant reduction in the total pre-oviposition period of S. graminum and a rise in its fecundity compared to the control. The intrinsic and finite rate of increase in S. graminum were affected by pre-infestation and their highest levels were observed in the 5-aphid pre-infested plant treatment. The highest level of net and gross reproductive rates were recorded in 5-aphid pre-infested plant treatment, whilst the lowest levels were observed in control. eva‎luation of wheat biochemical parameters under S. graminum stress showed that, H2O2 content was higher at 21º C in comparison to 25º C as oppose to MDA content which was higher at 25º C. H2O2 and MDA contents increased 24 and 48 hours after infestation at 21º C compared to control, but at 25º C these increases were observed only 24 hours after infestation. S. graminum feeding on wheat plant increased CAT, GPX and GST enzyme activities majority of the time. The activity of all investigated enzymes were higher at 25º C vs 21º C. The changes in H2O2 content and CAT and GST enzyme activities were similar at 25º C. There was a significant rise in GPX activity 48-hours after infestation unlike the H2O2 content. At 21º C, increase in H2O2 content caused a surge in GPX and GST enzyme activity after 24 and 48 hours however, CAT enzyme activity was increased only 24 hours post infestation. As a result, this research showed the defense response of wheat plant to S. graminum is affected by temperature, aphid feeding and the duration of feeding.

لادن طلايي

جهانگير خواجه علي

نفيسه پورجواد , محمدرضا سبزعليان دستجردي