Our objective was to identify traits in winter wheat important to competitiveness against jointed goatgrass, measured as increased wheat yields and reduced jointed goatgrass seed production. Jointed goatgrass is an important winter annual grass weed that cannot be controlled selectively in winter wheat. Seven cultivars of soft white winter wheat were grown with and without competition from jointed goatgrass over two growing seasons. Measurements of numerous traits of winter wheat and jointed goatgrass were recorded throughout each growing season. The data were analyzed using path analysis with latent variables to determine which traits most enhanced competitiveness. In a drier year, increased rate of height development was important in maintaining wheat yields when wheat was growing in competition with jointed goatgrass. Increased rate of height development also was an important trait in reducing jointed goatgrass seed production. In a wet year compared to a dry year, the number of wheat heads per plant, the rate of water use, and weight gain were positively correlated to maintaining winter wheat yields. Jointed goatgrass seed production in the wet year was reduced overall compared to the dry year, but from the cultivars tested, there were no traits identified that were critical in enhancing this loss of seed production. This study suggests that cultivars with greater height development rates will be more competitive when growing in fields infested with jointed goatgrass.

Imazamox-resistant hybrids resulted from a cross between jointed goatgrass and an imazamox-resistant wheat (cv. FS-4 IR wheat). Two imazamox-resistant hybrids were discovered in a research plot where FS-4 IR wheat seed had been replanted from the harvest of an imazamox efficacy study conducted the year before at a different location. These hybrid plants survived imazamox applied at 0.053 and 0.069 kg ai ha−1 in the field and produced seven viable seeds (BC1). This seed germinated, and chromosomes were counted from the roots (2N number ranged from 39 to 54). In the greenhouse, six of the seven plants survived an application of 0.072 kg ai ha−1imazamox, which confirmed that the resistance trait had been passed to these progeny. A large amount of phenotypic variation was observed in the mature BC1 plants. A genetic description of the movement of the resistant gene is proposed based on the case of the gene being located on the D and the A or B genomes. Management strategies to reduce the occurrence of herbicide-resistant hybrids are presented.

To assess the risk of gene movement between winter wheat and jointed goatgrass, information about the reproductive development of jointed goatgrass, winter wheat, and related hybrid plants is required. Seedlings from five jointed goatgrass populations, winter wheat, spring wheat, and jointed goatgrass by wheat reciprocal hybrid plants were exposed to 4, 7, or 10 C temperatures for 0, 2, 4, 5, 6, 6.5, 7, or 8 wk. Vernalized seedlings were transferred to a greenhouse set to 30/18 C day/night temperatures and 16-h photoperiod. Growth stages on all plants were recorded twice a week. All spring wheat and spring wheat related hybrid plants reproduced (as measured by the first reproductive node) in the absence of vernalization. Plants of jointed goatgrass population A-R, winter wheat, and winter wheat related hybrids were unlikely to reproduce in the absence of vernalization. Plants of jointed goatgrass populations B-W, G-S, E-S, and F-W reproduced in the absence of vernalization, and the likelihood that these plants would reproduce was different from all other plants. Plants that entered their reproductive phases together were not in synchronous development at anthesis. Plants in these studies differentially passed through the reproductive phases between the first reproductive node and anthesis. Our results demonstrate that variation in vernalization response exists among several jointed goatgrass populations, and reveal that the reproductive behavior of vernalized jointed goatgrass plants at anthesis is delayed compared to vernalized winter wheat and related hybrid plants. Hybrid plants produced between spring wheat and jointed goatgrass were vernalization insensitive. We hypothesize that hybridization between wheat and jointed goatgrass occurs as a result of cross-pollination between the younger reproductive tillers of jointed goatgrass and older reproductive tillers of wheat. The use of an early maturing wheat cultivar may exploit the difference in reproductive development and reduce the risk of hybrid production.

Gene flow between jointed goatgrass and winter wheat is a concern because transfer of herbicide-resistance genes from imidazolinone-resistant (IR) winter wheat cultivars to jointed goatgrass could restrict weed-management options for this serious weed of winter wheat cropping systems. The objectives of this study were (1) to investigate the frequency of interspecific hybridization between IR wheat and jointed goatgrass in eastern Colorado, and (2) to determine the gene action of the IR acetolactate synthase (ALS) allele in IR wheat by jointed goatgrass and in IR wheat by imidazolinone-susceptible (IS) wheat backgrounds. Jointed goatgrass was sampled side-by-side with IR wheat and at distances up to 53 m away in both experimental plots and at commercial field study sites in 2003, 2004, and 2005. A greenhouse-screening method was used to identify IR hybrids in collected jointed goatgrass seed. The average percentage of hybridization across sites and years when IR wheat and jointed goatgrass were grown side-by-side was 0.1%, and the maximum was 1.6%. The greatest distance over which hybridization was documented was 16 m. The IR ALS allele contributed 25% of untreated ALS activity in jointed goatgrass by IR wheat F1 plants, as measured by an in vitro ALS assay. The hybridization rate between wheat and jointed goatgrass and the expression of the IR wheat ALS allele in hybrid plants will both influence trait introgression into jointed goatgrass.

Numerous studies have quantified the developmental responses of wheat to vernalization, but its response compared to a weedy relative, jointed goatgrass, remains relatively unknown. Six paired jointed goatgrass collections gathered from Washington and Oregon fields, and winter and spring wheat, were grown in field studies to quantify yield and germination in response to vernalization. Monthly planting dates initiated in October and concluded in March were used to vary the vernalization durations for plants sown at three Oregon locations (Corvallis, Moro, and Pendleton) over two growing seasons. Minimum vernalization requirements to produce reproductive spikes were similar among plants of six jointed goatgrass collections. Jointed goatgrass collections grown at Corvallis required a minimum of 89 and 78 vernalization days (January 17, 2003 and January 22, 2004 sowing, respectively) to produce reproductive spikes, and plants grown at Moro required 60 vernalization days (March 3 and February 23) in both years, and 48 and 44 vernalization days (March 3 and February 24) were required by plants to produce spikes at Pendleton. Jointed goatgrass spikelet and winter wheat seed yield were positively influenced by vernalization days, experiment location, and year. The strength of the interactions among these main effects differed among jointed goatgrass collections and winter wheat. The effects of vernalization on jointed goatgrass yields and seed quality were more pronounced at Pendleton, OR, a location where jointed goatgrass has adapted, compared to Corvallis, OR, where it has not adapted. The minimum vernalization days required to produce germinable seed differed among jointed goatgrass collections, winter and spring wheat. There was not a selection of spring-adapted jointed goatgrass populations in the populations tested. Yet if spring temperatures are cool, minimum conditions for vernalization may be satisfied, and the benefits of planting spring crops to control jointed goatgrass would be reduced.

Integrated management techniques for several U.S. winter wheat production regions have been proposed for jointed goatgrass control. These strategies may be improved by a greater understanding of the genetic and environmental influences on seed production and germination. Plants from six jointed goatgrass collections were grown in common garden nurseries at two Oregon locations over two growing seasons. Unbroken spikes from each collection were used to evaluate seed dormancy and quantify seed production by inflorescence position. Germination tests were conducted over 14 d using spikelets of dormant and after-ripened samples in growth chambers set to 25/15 C day/night temperatures and a 12-h photoperiod. Spikelet position on the spike affected germination of the secondary seed in dormant samples of jointed goatgrass Collections D and G. In contrast, spikelet position did not affect secondary seed germination in dormant samples of Collection B. Spikelet position did not influence secondary seed germination in nondormant samples of all three collections. Spikelet position affected germination of the primary positioned seed in dormant samples of Collection B, and in nondormant samples of Collections B, E, and H. Unbroken spikes from jointed goatgrass Collections B and D were used to quantify seed production per spikelet position on the spike and per floret position within the spikelet. Seed production by floret position depended on spikelet position on the spike. This relationship varied for spikes of different lengths and for samples from the two collections. Efforts to model the life history of jointed goatgrass and predict germination should be adjusted to account for floret position within the spikelet, spikelet position within the spike, and source population. We suggest that future dormancy and germination research include sampling seed from several weed populations and efforts be made to standardize germination tests according to seed position on the inflorescence.

A survey conducted in a seven-county region of eastern Oregon during the summers of 1998, 1999, and 2000 characterized the occurrence of jointed goatgrass × wheat hybrids and the features of weed infestations promoting hybridization. During the survey, 93 infested sites were visited with jointed goatgrass collected from 57 sites and hybrids collected from 45 sites. Thirteen collection sites were located in uncultivated areas. Observations of jointed goatgrass infestations in and around cropped fields suggested that jointed goatgrass successfully escapes control where weed populations persist in fencerows, access roads, scablands, draws, and roadsides. Most jointed goatgrass and hybrid populations were located in winter wheat fields but were also found in five spring grain fields. Of the 754 hybrid plants collected, 44% contained backcross seed. For all 3 yr, a 1% backcross hybrid seed–production rate was found. A parentage analysis of a subsample of the total hybrid collection showed that the majority were F1 hybrids and that jointed goatgrass was most often the female parent. This observational study has established that F1 hybrids are common in jointed goatgrass–infested wheat fields. Their capability for backcross seed production suggests the potential development of advanced backcross forms that resemble jointed goatgrass. The survey results offer valuable input for the risk assessment of gene flow potential between jointed goatgrass and herbicide-resistant wheat.

Research during the past several decades on jointed goatgrass management has focused on individual cultural practices rather than on multi- or interdisciplinary components. Field studies were conducted at Hays, KS, from 1997 to 2003 to evaluate the interaction of crop rotation, fallow weed management, and winter wheat variety on jointed goatgrass density. Extending a wheat–fallow (W–F) rotation to include grain sorghum or grain sorghum and sunflower reduced jointed goatgrass populations more than other cultural practices tested. Fallow treatments were equal in most years, but mechanical fallow resulted in increased jointed goatgrass emergence compared with chemical fallow under drought conditions. Winter wheat cultivars had little effect on jointed goatgrass populations. However, taller, more competitive varieties are favorable for jointed goatgrass control in an integrated management program. No specific combination of crop rotation, fallow weed management, and wheat variety consistently reduced jointed goatgrass density more than other combinations during multiple years.

Jointed goatgrass is an important weed of wheat in the United States and other parts of the world. Under field conditions, wheat and jointed goatgrass can hybridize and produce backcross derivatives, a situation that may allow gene flow between these two species. In order to gain a better understanding of the factors governing gene flow, a study to characterize patterns of mating between these two species was undertaken. Chloroplast and nuclear microsatellite markers were used to evaluate the parentage of 413 first-generation backcross (BC1) seeds obtained from 127 wheat–jointed goatgrass F1 hybrids, produced naturally under field conditions. Of the 127 hybrids evaluated, 109 (85.8%) had jointed goatgrass as the female parent, whereas the remaining 18 F1 plants (14.2%) had wheat as the female parent. Of the 413 BC1 plants analyzed, 358 (86.7%) had wheat and 24 (5.8%) had jointed goatgrass as the male backcross parent. The male parentage of 31 BC1 (7.5%) plants could not be determined. Under natural field conditions, wheat was the prevalent pollen donor for the production of hybrids and first-generation backcross derivatives. However, hybrids and backcrosses with jointed goatgrass as the male parent also were observed. Thus, the establishment and persistence of a zone of hybridization between these species would result in the development of jointed goatgrass carrying wheat genes.

Field experiments were conducted in Oklahoma to quantify the wheat grain yield losses and price discounts resulting from season-long interference with cheat, feral rye, Italian ryegrass, jointed goatgrass, and wild oat. Plots were seeded to individual weeds at one of seven seeding rates, and wheat was planted in all plots at a uniform rate. Maximum weed densities were 89 (cheat), 80 (feral rye), 158 (Italian ryegrass), 170 (jointed goatgrass), and 120 plants/m2 (wild oat). Wheat grain yield losses caused by interference from the maximum density of each weed species were 19 (cheat), 55 (feral rye), 20 (Italian ryegrass), 21 (jointed goatgrass), and 28% (wild oat). Wheat grain total price discounts caused by interference from the maximum density of each weed species were 22 (cheat), 368 (feral rye), 26 (Italian ryegrass), 36 (jointed goatgrass), and 64 cents/hectoliter (wild oat). Of the five weed species included in this research, interference from feral rye had the greatest effect on wheat grain yield and price.

Greenhouse studies determined dose responses of winter annual weeds and winter wheat to preemergence (PRE) and postemergence (POST) treatments of MKH 6561 and the residual effects on kochia. MKH 6561 at 11 to 45 g ha−1 did not affect wheat. MKH 6561 at 11, 34, and 45 g ha−1 reduced winter annual weed densities compared to an untreated control. Weed growth was inhibited as the rate of MKH 6561 was increased, but downy brome, cheat, and Japanese brome were three to six times more susceptible than jointed goatgrass. The GR70 values for cheat, downy brome, Japanese brome, and jointed goatgrass were 7, 11, 4, and >45 g ha−1, respectively. Dry weights of kochia seeded after removal of the winter annual grasses decreased as MKH 6561 rate increased, with average control being 77% compared to the nontreated control. Regression analysis indicated that kochia was controlled 80% with MKH 6561 at 28 g ha−1.