Identification of an orthologous clade of peroxidases that respond to feeding by greenbugs (Schizaphis graminum) in C4 grasses.

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 ~30kb 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.

Levels of tolerance, antibiosis, and antixenosis among resistant buffalograsses and zoysiagrasses.

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.

Host preference of the chinch bug, Blissus occiduus.

The chinch bug, Blissus occiduus Barber (Hemiptera: Blissidae), is an important pest of buffalograss, Buchloë dactyloides (Nutall) Engelmann and potentially other turfgrass, crop, and non-crop hosts. Choice studies documented the number of B. occiduus present on selected turfgrasses, crops and weeds, and provided important insights into the host preferences of this chinch bug. Grasses with the most chinch bugs present included the warm-season turfgrasses B. dactyloides , zoysiagrass, Zoysia japonica Steudel, bermudagrass, Cynodon dactylon (L.) Pers., and St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze. The other grasses tested, green foxtail, Setaria viridis (L.) Beauv, Kentucky bluegrass, Poa pratensis L., perennial ryegrass, Lolium perenne L., rye, Secale cereale L., sorghum, Sorghum bicolor (L.) Moench, tall fescue, Festuca arundinacea Schreb. and wheat Tritium aestivum L. had significantly fewer chinch bugs. Buffalograss and zoysiagrass had the highest numbers of chinch bugs among the warm-season grasses and the buffalograss cultivars '86-120' and 'PX-3-5-1' had more chinch bugs than the zoysiagrass cultivars 'Meyers' and 'El Toro' after the two hour evaluation time.

Turfgrass, crop, and weed hosts of Blissus occiduus (Hemiptera: Lygaeidae).

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.); Kentucky bluegrass, Poa pratensis L.; perennial ryegrass, Lolium perenne L.; brome, Bromus spp. Leyss.; zoysiagrass, Zoysia japonica Steudel; Bermuda grass, Cynodon dactylon (L.) Pers.; sorghum, Sorghum bicolor (L.) Moench; tall fescue, Festuca arundinacea Schreb.; and barley Hordeum vulgare (L.). Slightly to nonsusceptible grasses included fine fescue, Festuca ovina hirtula L.; rye, Secale cereale L.; crabgrass Digitaria sanguinalis (L.); bentgrass, Agrostis palustris Huds.; wheat, Tritium aestivun L.; corn, Zea mays L.; fall panicum Panicum dichotomiflorum Michx.; and St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze. The reproductive potential of B. occiduus was also investigated on these same grasses. B. occiduus produced offspring on 15 of the 18 turfgrass, crop, and weed species evaluated. No reproduction occurred on either Bermuda grass or St. Augustinegrass, and buffalograss plants were killed by B. occiduus feeding before offspring could be produced.