J. A. Webster

Efficacy of Pyramiding Greenbug (Homoptera: Aphididae) Resistance Genes in Wheat

Abstract Durable resistance to greenbug, Schizaphis graminum (Rondani), in wheat is a goal of wheat improvement teams, and one that has been complicated by the regular occurrence of damaging biotypes. Simulation modeling studies suggest that pyramiding resistance genes, i.e., combining more than one resistance gene in a single cultivar or hybrid, may provide more durable resistance than sequential releases of single genes. We examined this theory by pyramiding resistance genes in wheat and testing a series of greenbug biotypes. Resistance genes Gb2, Gb3, and Gb6, and pyramided genes Gb2/Gb3, Gb2/Gb6, and Gb3/Gb6 were tested for effectiveness against biotypes E, F, G, H, and I. By comparing reactions of plants with pyramided genes to those with single resistance genes, we found that pyramiding provided no additional protection over that conferred by the single resistance genes. Based on the results of this test, we concluded that the sequential release of single resistance genes, combined with careful monitoring of greenbug population biotypes, is the most effective gene deployment strategy for greenbug resistance in wheat.

Tritrophic relationships of Russian wheat aphid (Homoptera: Aphididae), a hymenopterous parasitoid (Diaeretiella rapae McIntosh), and resistant and susceptible small grains

Abstract The tritrophic relationships between resistant small grain entries, Russian wheat aphid, Diuraphis noxia (Mordvilko), and Diaeretiella rapae McIntosh were studied. Resistant triticale entries with high levels of antibiosis affected growth and reproduction of both the aphid and the parasitoid. Parasitoid mummies from antibiotic triticale were smaller, took longer to develop, and were fewer in number compared with those from susceptible entries. The sex ratio of parasitoids emerging from the smaller mummies of aphids restricted to the resistant triticale entries was skewed toward females. The protective influence of parasitoids on plants was demonstrated in the experiment. Plants exposed to aphids without parasitoids sustained greater damage and had significantly less biomass than those so protected. A resistant wheat entry showed a reduction in aphid populations and enhanced parasitoid activity due to the fact that its leaves did not roll like those in the susceptible wheat entry.

Plant Resistance Components of Two Greenbug (Homoptera: Aphididae) Resistant Wheats

Abstract Several biotypes of the greenbug, Schizaphis graminum (Rondani), attack winter wheat, Triticum aestivum L., on the Southern Plains every year. Two wheat germplasm sources of resistance (‘Largo’ and ‘GRS 1201’) have been developed that provide protection against the three predominant greenbug biotypes (E, I, and K). Each source has agronomic and end-use quality advantages and disadvantages for the breeder to consider in choosing a greenbug-resistant breeding line. We compared these two germplasms to determine their levels of resistance against biotype E. Components of resistance (i.e., antibiosis, antixenosis, and tolerance) were measured on seedlings of GRS 1201, Largo, and ‘TAM W-101’ (a susceptible control). Several aphid and plant measurements (e.g., total number of aphids produced per plant, aphid selection preferences, and plant damage ratings) were recorded for each plant entry. Select data recorded for each resistance component were normalized and combined to derive a plant resistance index for each wheat entry. Results indicated that GRS 1201 had a higher level of combined resistance components than did Largo, followed by TAM W-101, the susceptible control. These data provide additional information for the breeder to consider in selecting a greenbug-resistant breeding line.

Russian wheat aphid-induced protein alterations in spring wheat

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), has become a perennial, serious pest of wheat (Triticum aestivum L.) in the western United States. Current methodologies used to enhance RWA resistance in wheat germplasm could benefit from an understanding of the biochemical mechanisms underlying resistance to RWA. This study was initiated to identify specific polypeptides induced by RWA feeding that may be associated with RWA resistance. The effects of RWA feeding on PI 140207 (a RWA-resistant spring wheat) and Pavon (a RWA-susceptible spring wheat) were examined by visualizing, silver-stained denatured leaf proteins separated by two-dimensional polyacrylamide gel electrophoresis. Comparisons of protein profiles of noninfested and RWA-infested Pavon and PI 140207 revealed a 24-kilodalton-protein complex selectively inhibited in Pavon that persisted in PI 140207during RWA attack. No other significant qualitative or quantitative differences were detected in RWA-induced alterations of protein profiles. These results suggest that RWA feeding selectively inhibit synthesis and accumulation of proteins necessary for normal metabolic functions in susceptible plants.

Probing Behavior of Diuraphis noxia and Rhopalosiphum maidis (Homoptera: Aphididae) Affected by Barley Resistance to D. noxia and Plant Water Stress

Abstract Probing behavior of Diuraphis noxia (Mordvilko), Russian wheat aphid, and Rhopalosiphum maidis (Fitch), corn leaf aphid, was measured on barley lines resistant and susceptible to D. noxia grown under low and high soil moisture. R. maidis reproduces similarly on both barley lines. Probing behavior was interpreted from waveforms of an alternating current electrical penetration graph (AC EPG) system of the Oklahoma design during 6-h monitoring periods. Significant effects were observed, particularly the aphid species by barley line interaction. Averaging across moisture levels, D. noxia took longer to first enter sieve element phase when probing D. noxia-resistant ‘STARS-9301B’ (306 ± 19.9 min [mean ± SEM]) than when probing susceptible ‘Morex’ (180 ± 21.6 min). In contrast, R. maidis relatively quickly entered sieve element phase on the two barley lines (average of 132 ± 13.7 min), with no detectable difference between lines. When measuring the total duration of sieve element phases, the stylets of D. noxia were in contact with phloem sieve elements of STARS-9301B for a shorter period (27 ± 10 min) than with sieve elements of Morex (111 ± 21 min). In contrast, stylets of R. maidis were in contact with sieve elements of the two barley lines for similar time periods (average of 176 ± 15.8 min). Any mediating effect of soil moisture was slight, if at all measurable, using the AC EPG system, making any interpretation of probing behavior relative to previous observations of aphid population growth affected by plant water stress untenable. In contrast, monitoring probing behavior was beneficial in assessing how plant resistance may affect aphid species differently. The differences in probing behaviors between the two aphids fed barley resistant and susceptible to D. noxia corresponded well with previous observations that D. noxia population growth was lower on D. noxia-resistant barley than on susceptible barley, while R. maidis population growth was similar on the two barley lines.

THE CEREAL LEAF BEETLE IN NORTH AMERICA: BREEDING FOR RESISTANCE IN SMALL GRAINS*

Many of the important insect pests of North American grain crops are introduced species. Familiar examples are the European corn borer, Ostrinia nuhilalis (Hiibner), first detected near Boston in 1917; the Hessian fly, Mayetiola destructor (Say) , found on Long Island as early as 1779; and the greenbug, Schizaphis gratninurn (Rondani), reported on small grains in Virginia in 1882 and currently the most serious pest of sorghum in the Middle West. Physiological races (biotypes) of all of these species have evolved since their introductions to North America.

Development of a triticale resistant to the greenbug: An historical perspective

SummaryA greenbug [Schizaphis graminum (Rondani)] resistant strain of rye (Secale cereale L.) ‘Insave F.A.’ from Argentina was crossed with ‘Chinese Spring’ wheat (Triticum aestivum L.) and also with ‘Elbon’ and ‘Balbo’ cultivars of common rye. Juvenile plants of the primary wheat X rye hybrid were treated with colchicine. Partially fertile amphidiploids were obtained that are resistant to greenbug Biotypes B and C. F1 and F2 populations of seedling plants derived from crosses of ‘Insave F.A.’ with ‘Elbon’ and ‘Balbo’ rye were tested for reaction to the greenbug to determine the genetic basis of inheritance. The results confirmed previous reports that resistance in ‘Insave F.A.’ is conditioned by a single dominant gene.

Charles Franklin Henderson 1901–1989

Charles Franklin Henderson died Jan. 2, 1989, in Rosewood Nursing Home in Stillwater, Okla.