Peroxidases play an important role in plant stress related interactions. This research assessed the role of peroxidases in the defense response of resistant and susceptible buffalograsses [Buchloe dactyloides (Nutt.) Engelm] and zoysiagrasses (Zoysia japonica Steudel) to the western chinch bug, Blissus occiduus Barber. The objectives were: (1) to assess the relationships among protein content, basal peroxidase levels, chinch bug injury, and ploidy levels of chinch bug-resistant and -susceptible buffalograsses;(2) to compare peroxidase activity levels of resistant and susceptible buffalograsses and zoysiagrasses in response to chinch bug feeding; (3) and to analyze extracted proteins from chinch bug-resistant and -susceptible buffalograsses and zoysiagrasses by native gel electrophoresis to obtain information on the peroxidase profiles. Correlation analyses of 28 buffalograss genotypes with varying levels of chinch bug resistance and ploidy levels indicated that buffalograss total protein content was correlated (r = 0.47, P = 0.01) to chinch bug injury, while basal peroxidase levels was not (r = 0.19, P = 0.29), suggesting that the up-regulation of peroxidases in resistant buffalograsses is a direct response to chinch bug feeding. Three of the four chinch bug-resistant buffalograss genotypes evaluated had higher peroxidase activity in the infested plants compared to control plants. Peroxidase activity levels were similar between infested and control plants of the two highly susceptible buffalograss genotypes. Zoysiagrasses had lower peroxidase activity in general when compared to buffalograss control plants, and only 'Zorro' consistently showed higher peroxidase activity in the infested plants. Native gel electrophoresis analysis identified differences in the isozyme profiles of infested and control buffalograsses 'Prestige' and 196, and the zoysiagrass 'Zorro'. Results from this study suggest that peroxidases have the potential to be used as markers for selecting chinch bug resistant turfgrasses, and may help explain how plants defend themselves against biotic stresses, such as chinch bugs.
Blissus occiduus Barber is an important pest of buffalograss, Buchloë dactyloides (Nuttall) Engelmann, turf. No-choice studies documented the susceptibility of selected turfgrasses, crops, and weeds to B. occiduus feeding. Highly to moderately susceptible grasses included buffalograss; yellow Setaria glauca (L.) and green foxtail Setaria viridis (L.
The western chinch bug, Blissus occiduus Barber, has been documented as one of the most serious pests of buffalograss, Buchloë dactyloides (Nuttall) Engelmann, and zoysiagrass, Zoysia japonica Steudel, grown for turf in midwestern states. Resistance to the western chinch bug has been identified in both buffalograsses and zoysiagrasses. Choice and no-choice studies were conducted to determine the categories (antibiosis, antixenosis, and tolerance) of three resistant buffalograsses (PX3-5-1', 196', and 184') and three resistant zoysiagrasses (El Toro, Emerald, and Zorro). Antibiosis studies found no significant differences in survival, nymphal development, or fecundity among the resistant and susceptible buffalograsses or zoysiagrasses, indicating that antibiosis is not an important factor in the resistance. Based on chinch bug damage ratings, 184, 196, and PX3-5-1 have comparable levels of tolerance to the known tolerant buffalograss 'Prestige', and Zorro was the most tolerant zoysiagrass. Choice studies indicated the presence of antixenosis in the buffalograss selection 196 and the zoysiagrass Emerald.
Knowledge of specific peroxidases that respond to aphid herbivory is limited in C4 grasses, but could provide targets for improving defence against these pests. A sorghum (Sorghum bicolor (L.) Moench) peroxidase (SbPrx-1; Sobic.002G416700) has been previously linked to biotic stress responses, and was the starting point for this study. Genomic analyses indicated that SbPrx-1 was part of a clade of five closely related peroxidase genes occurring within a ~30 kb region on chromosome 2 of the sorghum genome. Comparison of this ~30-kb region to syntenic regions in switchgrass (Panicum virgatum L.) and foxtail millet (Setaria italica L.) identified similar related clusters of peroxidases. Infestation of a susceptible sorghum cultivar with greenbugs (Shizaphis graminum Rondani) induced three of the five peroxidases. Greenbug infestation of switchgrass and foxtail millet plants showed similar inductions of peroxidases. SbPrx-1 was also induced in response to aphid herbivory in a greenbug-resistant sorghum line, Cargill 607E. These data indicate that this genomic region of C4 grasses could be valuable as a marker to assess potential insect resistance in C4 grasses.
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