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Published in Crop Sci. 43:2050-2057 (2003).
© 2003 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA

CROP BREEDING, GENETICS & CYTOLOGY

Resistance to Russian Wheat Aphid Damage Derived from STARS 9301B Protects Agronomic Performance and Malting Quality When Transferred to Adapted Barley Germplasm

Phil Bregitzer*,a, Dolores W. Mornhinwegb and Berne L. Jonesc

a USDA, ARS, National Small Grains Germplasm Research Facility, 1691 S. 2700 W., Aberdeen, ID 83210 USA
b Plant Science and Water Conservation Laboratory, 1301 N. Western St., Stillwater, OK 74075 USA
c Cereal Crops Research Unit, 501 N. Walnut St., Madison, WI 53075

* Corresponding author (pbregit{at}uidaho.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 CONCLUSIONS
 REFERENCES
 
Infestations of Russian wheat aphid (RWA), Diruaphis noxia (Mordvilko), reduce grain yield and quality of barley, and have induced producers in some areas to cease growing barley (Hordeum vulgare L.). No RWA-resistant barley cultivars that are adapted to North America exist. Resistance from the germplasm line STARS 9301B was transferred into adapted germplasm via backcrossing. Our objective was to determine the potential utility of this resistance for the protection of yield and malting quality in adapted germplasm. We studied the effect of RWA infestations on grain yield and malting quality of STARS 9301B, the susceptible adapted parents 88Y315 and ‘Garnet’, and five backcross-derived progeny. Four of the backcross-derived lines were rated as highly resistant and one as moderately resistant, and were superior to STARS 9301B and similar to their recurrent parents with respect to agronomic performances and, to a lesser extent, malting qualities. When infested at the boot to heading stage, STARS 9301B, and the highly resistant progeny lines had negligible reductions in agronomic performances and malting qualities; slightly greater reductions were observed for the susceptible parents and the moderately resistant progeny line. When infested at the three- to six-leaf stage, STARS 9301B and the resistant backcross-derived lines showed relatively small reductions in their agronomic performances and malting qualities. In sharp contrast, however, the susceptible parents, and to a lesser extent the moderately resistant progeny line, showed moderate to severe leaf streaking and rolling, head trapping, and reductions in their agronomic performances and malting qualities. STARS 9301B should provide a valuable source of resistance to RWA damage.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 CONCLUSIONS
 REFERENCES
 
THE RUSSIAN WHEAT APHID has caused over $1 billion in losses in the western USA since it was first identified in Texas in 1986. No biotypic variation has been discovered among RWA populations in the USA (Shufran et al., 1997). Although the RWA has yet to adapt to the more humid, lower elevation areas east of the Rocky Mountains, it is a persistent pest to western barley growers in certain regions, especially during hot, dry years. RWAs are effectively protected from contact insecticides because the aphid prevents leaves from unrolling, and can only be controlled by systemic insecticides which are relatively expensive, toxic, and more likely to accumulate in the grain and other end products. Some areas of Colorado, Wyoming, and Nebraska no longer produce barley because of the presence of RWA, where the cost of chemical control under low-productivity, dryland environments is prohibitive. All U.S. barley cultivars are susceptible to RWA. Greenhouse screening of the entire USDA National Small Grains Collection of Hordeum vulgare (23 070 accessions) identified 109 resistant accessions that had some level of seedling resistance to RWA (Porter et al., 1999). Thirty-four of the accessions were highly resistant and were rated 2 to 3 on Webster's scale of 1 to 9 (1 = immune, 9 = dead) (Webster et al., 1991). STARS 9301B, which rated 2 on Webster's scale, was the first RWA-resistant barley germplasm released (Mornhinweg et al., 1995a) followed by the release of STARS 9577B (Mornhinweg et al., 1999), which was rated 3 on Webster's scale. The resistance in STARS 9301B is controlled by two genes, Rdn1 and Rdn2 (Mornhinweg et al., 1995b), and resistance in STARS 9577B has also been determined to be under the control of two genes (Mornhinweg et al., 2002).

Calhoun et al. (1991) found that RWA infestations of barley at the three-leaf stage negatively affected grain yield, spike number, and straw yield, but had no effect on 100-kernel weight. Kieckhefer and Gellner (1992) found that 30-d exposure of wheat to RWA feeding at the seedling stage negatively affected tiller number. Robinson et al. (1992) showed that there was good correlation between greenhouse seedling RWA ratings and field seedling ratings but suggested that resistance that was assessed on seedlings in the greenhouse may not reflect the field resistance of mature plants. Mornhinweg et al. (1992) grew 11 barley lines that differed in their RWA seedling resistance ratings to maturity in the greenhouse under constant RWA infestation. By maturity, the RWA populations in this greenhouse test were 100-fold those of normal field populations. The lines that were rated resistant or moderately resistant as seedlings in the greenhouse remained resistant through maturity. The grain yields of the resistant lines were not affected by the RWA feeding while the yields of moderately resistant lines were reduced by the RWA feeding but not significantly. Moderately susceptible and susceptible lines did not live to produce seed. A 2-yr field study in Wyoming of 18 unadapted RWA-resistant barley germplasm lines that differed in their seedling RWA resistance ratings from 2 to 6 on Webster's 1-to-9 scale showed that greenhouse seedling resistance ratings accurately predicted field resistance (Mornhinweg, unpublished). In these experiments, plots were artificially infested with RWA at two growth stages, early (seedlings) and late (heading). Even with early infestation, the resistant lines showed no significant reductions in their grain yields, while moderately resistant lines had moderate reductions in their grain yields and moderately susceptible and susceptible lines had severe reductions in their grain yields. Since aphids were present on these tolerant lines, it was of interest to discover whether RWA feeding could affect the structure and enzyme function of the grain and therefore malting quality, despite the absence of measurable reductions in yield. However, the inherently very poor malting qualities of these germplasm lines prevented any meaningful assessment of the commercial utility of resistance for the protection of malting quality under RWA feeding pressure.

In this study, advanced generation adapted RWA-resistant barley germplasm lines, which were developed cooperatively by the USDA-ARS at Aberdeen, ID, and Stillwater, OK, were artificially infested with RWA at both an early (three- to six-leaf stage) and late (boot to heading stage) date. RWA resistance in these lines was derived from STARS-9301B. Our objective was to determine the effect of RWA feeding on the malting qualities and agronomic performances of these resistant lines.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 CONCLUSIONS
 REFERENCES
 
Population Development
Eight barley lines were tested, including the RWA-resistant parent, STARS 9301B, the RWA-susceptible parents ‘Garnet’ and 88Y315, and five backcross-derived lines (two had 88Y315 as the recurrent parent and three had Garnet as the recurrent parent) as BC1F4:8 (BC1F4–derived F8) and BC1F4:9 populations (Table 1). All backcross populations were produced by a modified pedigree, head-to-row selection system through the BC1F5 generation. Selections were made under high-input, irrigated, and highly productive conditions at Aberdeen. F1 populations were produced in the greenhouse during the summer of 1992, and used to produce BC1F1 populations in the greenhouse during the winter of 1992-1993. BC1F1 populations were space-planted in the field at Aberdeen in 1993, and individual heads were harvested on the basis of agronomic appearance. BC1F1:2 plants were tested for RWA resistance in the greenhouse at Stillwater where 30 seedlings per line were infested at emergence and rated, according to Webster's scale (Webster et al., 1991), after approximately 3 wk. BC1F2:3 seed from resistant plants was planted in short headrows in the field at Aberdeen in 1994. Individual heads showing good kernel plumpness were harvested from agronomically attractive plants. BC1F3:4 plants were tested for RWA resistance as described above, and BC1F4:5 seed from resistant plants was planted in the field at Aberdeen in 1995. Agronomically attractive rows were harvested in bulk and 30 seedlings were screened for RWA resistance. Homozygous selections showing a homogeneous, resistant reaction were entered into yield trials as BC1F4:6 lines at Aberdeen and Tetonia (a high-elevation, dryland, moderately productive site), ID. The five backcross-derived, RWA-resistant lines used for this study were selected on the basis of their agronomic performance in these trials.


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  		Table 1. Agronomic performance of RWA-susceptible recurrent parents, the RWA-resistant donor parent, and RWA-resistant backcross-derived lines, grown in 1998 and 1999 at Aberdeen, ID, and Fort Collins, CO, in the absence of RWA infestations.

 
Experimental Design and Conduct
The tested lines were planted at Aberdeen, ID, and Fort Collins, CO, in a split plot design with four replicates using lines as the main plot and aphid treatment levels (early infestation, late infestation, and no infestation) as the split plots. Each plot consisted of four rows planted on approximately 36-cm centers; at Aberdeen, the plots were 2.4 m in length and at Fort Collins they were 4.6 m in length. At Aberdeen, the plots were planted approximately 2 wk later after other spring grain trials to reduce the probability that winged aphids would migrate to adjacent trials of spring grain. Each barley plot was separated from adjacent plots by a 1.2-m alley (front and back) and an oat (Avena sativa L.) plot (side to side); at Fort Collins, the plots were adjacent to each other but separated by a 1.2-m alley (front to back). The plots were irrigated by overhead sprinklers (Aberdeen) or furrow irrigation (Fort Collins).

At Fort Collins, the three infestation levels were obtained with three levels of Gaucho, Bayer Agricultural Products, Kansas City, MO {imidicloprid---1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine, 1-[(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidinimine} seed treatment. Seed for noninfested, late infested, and early infested plots were treated with 0.24, 0.03, and 0 L of Gaucho (imidicloprid 40.7%) per 45 kg of seed, respectively. At Aberdeen, noninfested control plots were treated with Cygon, BASF, Mount Olive, NJ [dimethoate---O,O-dimethyl S-(N-methylcarbamoylmethyl) phosphorodithioate] insecticide, which was applied as a 0.23% a.i. spray per manufacturer's directions on four dates at approximately 2-wk intervals starting shortly after the first infestation was made. Late infested plots at Aberdeen were kept aphid-free also by spraying until the late boot stage while early infested plots were never sprayed. Artificial infestation of early infested plots was accomplished by placing leaves from greenhouse-grown, RWA-infested barley plants next to the rows (all rows at Fort Collins, only the center two rows at Aberdeen) when the plants had reached approximately the three- to six-leaf stage, and aphids were allowed to migrate onto plants within the plots. Late infested plots were artificially infested with RWA as described above at approximately late-boot to heading growth stages.

At Aberdeen, the number of RWAs per tiller was counted by hand on 10 randomly harvested tillers per plot at three dates throughout the growing season in 1998 and two dates in 1999. Damage ratings for leaf rolling and streaking were based on a 0-to-3 rating scale, where 0 = no rolling or streaking and 3 = severe rolling or streaking, and were based on observation of the same tillers used to determine RWA populations. At Fort Collins, RWA infestation numbers were determined at heading by harvesting 20 randomly harvested tillers from each plot, and placing them in Berlese funnels; aphids were counted after 24 h. Damage ratings at Fort Collins were taken on a per-plot basis approximately 20 d before tiller sampling for aphid counts.

Agronomic data were collected for days to heading (Aberdeen location only), plant height, percent lodging, grain yield, test weight, and percent plump kernels. All rows of each plot were harvested by a small-plot combine at Fort Collins. At Aberdeen, the center two rows were cut, bound, and threshed with a Vogel thresher. Malt was prepared from grain samples (170 g dry weight) and its quality analyzed at the USDA-ARS Cereal Crops Research Unit, Madison, WI, following standard micromalting and analysis techniques. Detailed information on these malt quality analyses can be found at http://www.dfrc.ars.usda.gov/ccru/ccru.html (verified 11 June 2003) as appendices to the Crop Year Reports.

Statistical Analysis
A split-plot design using lines–cultivars as the main plots and aphid infestation dates (treatments) as the split plots was used. Data were analyzed by the PROC MIXED analysis of variance software (SAS institute version 7.0, SAS Institute, Inc., Cary NC). The effects specified as random included rep, rep within location and year, and genotype x rep within location and year; the remainder of the effects were specified as fixed. The Satterthwaite method was used to estimate the denominator degrees of freedom. Comparisons of line–cultivar x treatment means were based on differences of least squares means, P = 0.05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
CONCLUSIONS
 REFERENCES
 
Control of Aphid Infestations
The three treatments (uninfested, late infested, and early infested) were successfully isolated, i.e., aphids did not migrate to any appreciable extent from the early infested to the late infested plots before the late infestation date, and the use of insecticide kept the uninfested plots virtually aphid-free throughout the experiment. The levels of infestation varied markedly between years and test locations. Details on the development of aphid populations are discussed later in this report.

Agronomic Performance
The agronomic performances of the susceptible recurrent parents, the resistant donor parent, and the backcross-derived lines are shown in Table 1. STARS-9301B had very poor agronomic characteristics; in particular, it had low grain yield, very weak straw, and small, thin kernels. In contrast, the susceptible parents had excellent agronomic characteristics. Both susceptible parents are products of the USDA-ARS breeding program at Aberdeen, ID. Garnet is a recently released malting cultivar (Wesenberg et al., 2000). 88Y315 is an advanced breeding line that is not scheduled for release.

Garnet, 88Y315, and STARS 9301B each have distinctive, dissimilar morphological characteristics. Although a single backcross could not produce near-isogenic lines, the distinctive morphologies of the recurrent parents were recovered to a significant extent in the backcross-derived progenies. Furthermore, the agronomic performances of these progeny lines were more similar to the recurrent parents than to STARS 9301B, and thus we considered that the progeny lines were representative of commercially adapted germplasm. The high RWA resistance of STARS 9301B was recovered in all progeny lines except 95RWA96, which was only moderately resistant to RWA damage. RWA resistance in STARS 9301B is conditioned by two loci (Mornhinweg et al., 1995b), and it is possible that 95RWA96 contains the resistant alleles at only one of these loci.

Infestation with RWAs at the three- to six-leaf (early) stage had marked and severe effects on the susceptible parents. Within days of the infestation, newly emerging leaves developed streaks that ranged from slightly chlorotic to albino, and failed to unroll, somewhat reminiscent of plants grown under extreme drought stress (Fig. 1). To a lesser extent, 95RWA96, which had been rated in greenhouse screens as moderately resistant, also developed these symptoms. The heads that developed on tillers that had severely rolled leaves frequently were trapped and did not extrude from the flag leaf sheath; this was particularly true for Garnet (Fig. 2). On such heads, seed development was severely reduced, both for the percentage of florets which set seed and for the size of the mature kernels. In sharp contrast to the reactions of the susceptible parents, the resistant parent, STARS 9301B, and the four resistant backcross-derived lines were essentially asymptomatic (Fig. 1 and 2).



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  		Fig. 1. Typical plots grown at Aberdeen, 1998, before heading. Top photographs are of Garnet, bottom photographs are of 95RWA82. Left photographs are of noninfested plots and right photographs are of plots which were infested with RWAs at the three- to six-leaf stage. Plots of oat are on the immediate left and right of each barley test plot.

 


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  		Fig. 2. Typical plots grown at Fort Collins, 1998, before harvest. Top photographs are of Garnet, bottom photographs are of 95RWA82. Left photographs are of noninfested plots and right photographs are of plots which were infested with RWAs at the three- to six-leaf stage.

 
Infestation at the boot-to-heading (late) stage resulted in similar symptoms in late-developing tillers, particularly on the susceptible parent Garnet. These symptoms were only obvious under close inspection, as the older tillers which were near or at heading stage did not develop leaf streaking or rolling to any significant degree. The moderately resistant line 95RWA96 was largely asymptomatic when infested at this stage, and STARS 9301B and the four resistant backcross-derived lines were completely asymptomatic.

Infestation with RWAs resulted in varying reductions in the agronomic performances of the tested lines. These were generally consistent with the symptoms described above and with the resistance scores that had been determined in greenhouse tests. The relative levels of damage varied from year to year and between the locations, in large part as a consequence of variable infestation levels (see later in this report). Predictably, this resulted in statistically significant interactions involving years and locations with treatments and cultivar–line responses. A careful examination of the data indicated that such interactions did not derive from changes in rank relationships among treatments or lines, but from changes in the magnitudes of the responses. Thus, examination of the main effects averaged across years and locations resulted in the same conclusions as did individual examinations of the data from each location and year. These data are presented in Table 2. The susceptible parents had significant reductions for all measured characteristics when infested at the early growth stage, and for most measured characteristics when infested at the later stage. Garnet showed drastic reductions in agronomic performance, and its yield was reduced to 24% of the noninfested control. 88Y315 performed relatively better than Garnet, but still showed significant reductions in performance. 95RWA96, which was rated as only moderately resistant, performed better than Garnet but still was greatly affected by RWA infestations.


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  		Table 2. Agronomic performance of resistant and susceptible barley lines grown in 1998 and 1999 at Aberdeen, ID, and Fort Collins, CO, in response to Russian wheat aphid infestations, as a percent of the uninfested control performance.

 
In contrast, the resistant parent, STARS 9301B, and the four backcross-derived lines that were rated as resistant performed relatively well in the presence of RWA infestations (Table 2). Late infestation caused no significant reductions of plant heights or grain yields for any of these lines, although slight reductions in test weights, plump kernel percentages, and kernel weights occurred in many cases. Interestingly, these reductions were about the same as those that were noted for the susceptible parents. However, when infested at the early date, none of these lines showed the severe reductions in performance that were seen for the susceptible parents and the moderately resistant backcross-derived line. The heights of the resistant lines were not affected, and yield was reduced significantly only for 95RWA214, and the percentage reduction (relative to the noninfested control) was relatively less than the susceptible parent, 88Y315. The test weights (except for 95RWA154, 95RWA82, and STARS 9301B), plump kernel percentages, and kernel weights were significantly reduced in all resistant lines, although the extent of these reductions was far less than that of the susceptible parents.

Malting Quality
Data for the malting quality of the susceptible recurrent parents, the resistant donor parent, and the backcross-derived lines, are shown in Table 3. These data will be discussed with reference to acceptable standards of malting quality (Table 4). The 6-rowed resistant parent, STARS 9301B, had very poor malting quality. Its extract and soluble (wort) protein values were very low, while its total (barley) protein and ß-glucan levels were unacceptably high. STARS 9301B had very good diastatic power levels, even though its {alpha}-amylase levels were quite low. The high ß-glucan levels and low extract and soluble protein values indicated that this line did not modify well when malted using our standard schedule; that is, the desired biochemical modifications necessary to produce good malt were not completely achieved.


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  		Table 3. Malting quality characteristics of RWA-susceptible recurrent parents, the RWA-resistant donor parent, and RWA-resistant backcross-derived lines, grown in 1998 and 1999 at Aberdeen, ID and Fort Collins, CO, in the absence of RWA infestations.

 

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  		Table 4. Acceptable values for selected characteristics for commercial malting barley cultivars.

 
The malting qualities of the RWA-susceptible parents varied. Garnet, a malting barley approved for commercial use by the American Malting Barley Association, showed reasonably good malting quality. Its total protein level was a slightly high. This was probably at least partially due to environmental effects, since all of the tested lines had elevated protein contents, most of which were unacceptably high. Garnet's amylolytic (diastatic power and {alpha}-amylase) enzyme activities were also a little high. The three lines that were developed from backcrosses to Garnet generally had levels of soluble protein and amylolitic enzyme activity and ß-glucan that were preferable to those of the Garnet parent and that were much superior to those of STARS 9301B. Their extract values were lower than those of Garnet but higher than those of STARS 9301B.

88Y315 showed intermediate malting quality, yielding low extract and high wort protein, {alpha}-amylase, and ß-glucan levels. As expected, the 88Y315 backcross progeny exhibited intermediate characteristics for many of the malting quality parameters. The protein and ß-glucan levels of 96RWA154 were still too high and its extract level was too low, but the overall quality was clearly superior to the STARS 9301B parent. All of the quality parameters of 96RWA214 were better than those of STARS 9301B and its overall quality was approaching acceptable, except for its low extract and high ß-glucan values. The overall quality of 95RWA214 was slightly better than that of 88Y315.

Table 5 presents how well or poorly the various barley quality parameters withstood RWA infestations. An examination of the malting quality for the two treatments indicates that all of the plants, including the susceptible parents, survived the late infestation without any appreciable change in malting quality. There were some significant differences (P = 0.05) in a few of the parameters, but these differences were very small and had little effect on the actual malt quality. When the RWA infestations were present early in the plant development, some very obvious quality changes occurred. These changes were more substantial in the susceptible parents, and in moderately resistant line 95WA96, than in the resistant parent or the resistant backcross-derived lines. The susceptible parents both showed strong increases in their total protein, soluble protein, diastatic power and ß-glucan values, while their extract and soluble/total protein values all dropped. Many of these changes—especially to protein content, enzymatic activities, and extract—are likely to be reflections of the reduced carbohydrate content present in the smaller kernels of the infested plants. The susceptible barleys all suffered greatly from the depredations of the aphids. STARS 9301B, however, took the aphids in stride and maintained its (admittedly poor) malting quality, even when infested early in its development. The backcross-derived lines were generally more resistant to damage than the susceptible parents and less resistant than STARS 9301B. With the exception of 95RWA96, all of the progeny lines showed a marked ability to produce good malt, relative to their susceptible parents. The malting quality of the moderately-resistant line, 95RWA96, was strongly degraded as a result of early infestation, although it was slightly less affected than its susceptible parent, Garnet.


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  		Table 5. Malting quality characteristics of resistant and susceptible barley lines grown in 1998 and 1999 at Aberdeen, ID and Fort Collins, CO, in response to Russian wheat aphid infestations, as a percent of the uninfested control performance.{dagger}

 
Relationships between RWA Population Pressure, Damage Symptoms, and Grain Yield
While the data presented in Tables 1, 2, 4, and 5 accurately summarize the overall effect of RWA damage and of the effectiveness of the STARS 9301B-derived resistance, RWA populations differed greatly between years and locations. Examination on a year-by-location basis of RWA populations and the resultant damage provides additional understanding of the relationships between RWA populations and economic damage (Tables 6 and 7).


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  		Table 6. Russian wheat aphid populations, symptom development, and grain yield of resistant and susceptible barley lines and cultivars grown at Aberdeen, ID.

 

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  		Table 7. Russian wheat aphid populations, symptom development, and grain yield of resistant and susceptible barley lines and cultivars grown at Fort Collins, CO.

 
The very low RWA populations that developed in 1998 at Aberdeen produced surprisingly severe damage to the susceptible parents when infested at the early date, even though trapped heads were not observed. RWA damage to susceptible parents was relatively more severe at the other test locations, where aphid populations were larger, but the expected negative relationship of yield and RWA population was not apparent (Tables 6 and 7). The occurrence of leaf streaking and rolling, and head trapping was more consistently associated with yield reductions than was the number of RWAs (Tables 6 and 7), although the relative differences in yield reductions of Garnet, 88Y315, and 95RWA96 infested at the early date were greater than the differences in their leaf rolling and streaking scores. This may reflect a deficiency in the 0-to-3 rating scale used to assess rolling and streaking, as a comparison of the overall visual appearance of the test plots of these three lines in the field with yield reductions showed a very good relationship (data not shown). When infested at the early date, plots of the Garnet rapidly developed a distinctly damaged appearance and had severe reductions in yield. In comparison, plots of 88Y315 and 95RWA96 infested at the early date did not appear to be as badly damaged, and yield reductions were relatively smaller than observed for Garnet.

Previous observations of the STARS 9301B-derived resistance have established tolerance, and not antibiosis, as the primary mechanism of resistance (Webster et al., 1991). In numerous assays for RWA resistance conducted in the greenhouse, RWA populations have developed essentially equally on resistant and susceptible plants (Mornhinweg, unpublished). Thus, the observation of far larger RWA populations on the susceptible parents relative to the resistant lines and STARS 9301B was unexpected. The explanation for this observation may be that the normal development (unrolling) of leaves on the resistant lines exposes the RWAs to predators and parasites. Furthermore, compared with other cereal aphids that do not interact with the plant to produce the protection of tightly rolled leaves, RWAs are extremely easy to dislodge from the plant. Wind, rain, and sprinkler irrigation may thus reduce RWA population development on resistant plants.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 CONCLUSIONS
REFERENCES
 
This study clearly demonstrates that RWA populations, even if relatively small, can have devastating effects on the yield and quality of susceptible barley if infestations occur early in the growth cycle of the crop. Infestations that occur around or after the boot stage, however, result in less damage. Nevertheless, the reductions in grain yield (about 10%) recorded even for late infested barley would be significant to barley producers.

The germplasm line STARS 9301B maintained its agronomic and malting quality characteristics even under high RWA populations that occurred early in the growth cycle. Furthermore, four of the five tested backcross-derived lines showed resistance that was equivalent to that of STARS 9301B. The fifth line, 95RWA96, was only moderately resistant, and was significantly damaged by RWA infestation, although it sustained less damage than its susceptible parent, Garnet. It is possible that both of the resistance genes from STARS 9301B were not recovered in this line. The classification of the tested lines and cultivars as resistant, moderately resistant, or susceptible before these field tests was based solely on seedling screens conducted in the greenhouse. This study shows that these seedling screens accurately predicted field reaction to RWA feeding.

No RWA-resistant barley cultivar has been released in the USA, and none of the resistant lines tested for this study have the necessary characteristics for commercial success. None of these lines would be acceptable for malting by current industry standards. None would be competitive with the best available feed cultivars for yield, and although lodging was not severe in these trials, we have observed in other trials that these lines do not have acceptable straw strength.

Nevertheless, these results are encouraging in that high levels of RWA resistance were recovered in breeding lines which were reasonably similar to their elite, recurrent parents. These lines were developed from a very weak-strawed, low yielding donor parent with just one backcross, and from relatively small populations. Thus, further breeding efforts likely could produce commercially competitive barley lines that have the high level of RWA resistance found in STARS 9301B. Since the time that the lines tested in this study were developed, further development of RWA-resistant barleys has produced elite germplasm that combines strong straw, high grain yield, test weight, and kernel plumpness, and which appear to be commercially competitive across a wide range of environments (Bregitzer and Mornhinweg, unpublished data). Malting qualities in several of these lines also approach commercial acceptability. Two of these advanced lines (98ID242 and 97ID1269B) were tested in the 2002 Western Regional Barley Nurseries and were agronomically competitive in a number of environments (results of these tests can be viewed at http://www.ars-grin.gov/ars/PacWest/Aberdeen/barnur.htm; verified 11 June 2003). Thus, it appears possible to produce commercially useful barley germplasm that is highly resistant to damage from RWA feeding by incorporating the resistance genes from STARS 9301B.

Received for publication January 17, 2003.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 CONCLUSIONS
 REFERENCES
 




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D. W. Mornhinweg, P. P. Bregitzer, and D. R. Porter
Registration of Nineteen Spring Six-Rowed Barley Germplasm Lines Resistant to Russian Wheat Aphid
Journal of Plant Registrations, September 1, 2007; 1(2): 137 - 138.
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D.W. Mornhinweg, D.E. Obert, D.M. Wesenberg, C.A. Erickson, and D.R. Porter
Registration of Seven Winter Feed Barley Germplasms Resistant to Russian Wheat Aphid
Crop Sci., June 20, 2006; 46(4): 1826 - 1827.
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D. W. Mornhinweg, M. J. Brewer, and D. R. Porter
Effect of Russian Wheat Aphid on Yield and Yield Components of Field Grown Susceptible and Resistant Spring Barley
Crop Sci., December 2, 2005; 46(1): 36 - 42.
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J. M. Bonman, H. E. Bockelman, L. F. Jackson, and B. J. Steffenson
Disease and Insect Resistance in Cultivated Barley Accessions from the USDA National Small Grains Collection
Crop Sci., May 27, 2005; 45(4): 1271 - 1280.
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P. Bregitzer, D.W. Mornhinweg, R. Hammon, M. Stack, D.D. Baltensperger, G.L. Hein, M.K. O'Neill, J.C. Whitmore, and D.J. Fiedler
Registration of 'Burton' Barley
Crop Sci., May 6, 2005; 45(3): 1166 - 1167.
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