Entomology, Department of


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A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillments of Requirements For the Degree of Master of Science, Major: Entomology, Under the Supervision of Professors Tiffany M. Heng-Moss and Gautam Sarath. Lincoln, Nebraska: December 2010


In recent years, buffalograss, Buchloë dactyloides (Nuttall) Engelmann has gained popularity as a turfgrass because of its low maintenance requirement, drought tolerance, and limited pests and diseases. Within the last decade, however, the western chinch bug Blissus occiduus Barber has emerged as important pest of buffalograss. Considerable progress has been made toward identifying buffalograsses with resistance to the western chinch bug and understanding the mechanisms of the resistance. It has been hypothesized that chinch bug-resistant buffalograsses can effectively detoxify the elevated levels of Reactive Oxygen Species (ROS) through enhanced activity of ROS-scavenging enzymes, while ROS accumulates in the susceptible plants because of the inability of the plant to detoxify these compounds. The objectives of this research were to document the accumulation of hydrogen peroxide and the levels of peroxidase and catalase in both control and B. occiduus challenged buffalograsses. Two genotypes of buffalograss were evaluated: the chinch bug-resistant (tolerant) cultivar, Prestige, and chinch bug-susceptible cultivar, 378. Histochemical (diaminobenzidine; DAB) staining techniques were employed to document hydrogen peroxide accumulation and catalase activity. Hydrogen peroxide levels were also detected at the ultrastructural level using cerium. Chinch bug infested Prestige plants had higher levels of hydrogen peroxide accumulation relative to their control plants and chinch bug infested 378 plants. According to DAB staining for catalase activity, both infested 378 and Prestige plants had higher levels of catalase activity initially when compared to their uninfested control plants. However, by day 11 following insect introduction, infested Prestige plants showed a higher apparent level of catalase accumulation as compared to infested 378 plants. In addition, enzyme kinetic studies revealed a higher level of peroxidase activities in 378 plants in response to chinch bug feeding at early time points. However, at later time points both control and infested plants showed similar levels of peroxidase activity. By contrast, infested Prestige plants exhibited significantly higher or similar levels of peroxidase activity to their control plants. Chinch bug infested 378 plants had a lower level of catalase activity relative to their control plants, while similar levels of catalase were observed in chinch bug-infested and control Prestige plants. This research supports our working hypothesis on the importance of hydrogen peroxide and oxidative enzymes in the response of tolerant and susceptible buffalograss plants to chinch bug feeding. The ultimate goal of this research is to help identify the mechanisms underlying the tolerance traits in resistance plants to chinch bug.

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