Bread wheat and durum wheat genotypes were grown in field experiments at two locations in New South Wales, Australia across several years and using two sowing times (‘early’ v. ‘late’). Genotypes were grouped based on genetic similarity. Grain yield, grain size, soil characteristics and daily weather data were collected. The weather data were used to calculate water and heat stress indices for four key growth periods around flowering. Least absolute shrinkage and selection operator (LASSO) was used to predict grain yield and to identify the most influential features (a combination of index and growth period). A novel approach involving the crop water supply–demand ratio effectively summarized water relations during growth. LASSO predicted grain yield quite well (adjusted R2 from 0.57 to 0.98), especially in a set of durum genotypes. However, the addition of other important variables such as lodging score, disease incidence, weed incidence and insect damage could have improved modelling results. Growth period 2 (30 days pre-flowering up to flowering) was the most sensitive for yield loss from heat stress and water stress for most features. Although one group of bread wheat genotypes was more sensitive to water stress (drought) in period 3 (20 days pre-flowering to 10 days post-flowering). Evapotranspiration was a significant positive feature but only in the vegetative phase (pre-flowering, period 1). This study confirms the usefulness of LASSO modelling as a technique to make predictions that could be used to identify genotypes that are suitable candidates for further investigation by breeders for their stress-tolerance ability.

Drought is a substantial threat to cereal production under global climatic change scenarios, albeit its aftermath on arthropod pests is yet contentious. To address this issue, demographic characteristics of Metopolophium dirhodum (Walker, 1849) (Hemiptera: Aphididae) were studied on one drought-susceptible wheat cultivar and one drought-tolerant wheat cultivar under different water treatments. Some physiological and biochemical features of wheat cultivars including leaf soluble sugar and proline contents and antioxidant enzymes activities were also investigated. Significant differences occurred in the developmental period, survival, and fecundity of M. dirhodum between wheat cultivars under various water treatments. The impact of intermediate and severe water stress on M. dirhodum was neutral and negative for the tolerant cultivar and negative for the water-susceptible cultivar, respectively. Under severe water stress, on both wheat cultivars, the aphids had low net reproductive rates and finite and intrinsic rates of increase in comparison with those reared on unstressed plants. In total, drought resulted in lower growth of population and reduced survival of aphids. Hence, in the context of projected climatic changes, acute water deficiency could probably result in reducing the abundance and menace of outburst of M. dirhodum. However, it should be noted that the potential likelihood of M. dirhodum eruptions can be drastically affected by the degree of drought intensity and host plant cultivar.

Fusarium head blight (FHB) and stem rust (SR) threaten the sustainability of wheat production worldwide. Fhb1 and Sr2 confer partial durable resistance to FHB and SR, respectively. Despite resistant alleles of both genes are linked in repulsion, lines with Fhb1-Sr2 in coupling were developed at the University of Minnesota, USA. Marker-assisted backcrossing was used to incorporate the coupled Fhb1-Sr2 into four elite INIA-Uruguay spring wheat varieties lacking both genes and expressing different levels of FHB and SR resistance. In each case, the initial cross between the donor line and recurrent parent was backcrossed three times. Genotypes carrying Fhb1-Sr2 were selected using the molecular marker UMN10. In BC3F3 families, retention of Fhb1-Sr2 was further confirmed with the markers SNP3BS-8 and Sr2-ger9 for Fhb1 and Sr2, respectively. BC3F3 homozygous lines contrasting at UMN10, SNP3BS-8 and Sr2-ger9 were obtained to quantify the effect of Fhb1-Sr2 on the resistance to FHB under controlled conditions and to SR under field conditions. After 26 months period, successful introgression of Fhb1-Sr2 into the four cultivars was achieved, representing novel wheat genetic resources. Lines homozygous for the resistant alleles of Fhb1 were significantly more resistant to FHB as reflected by an 18% reduction of average FHB area under the disease progress curve. A significant effect of Sr2 on SR field resistance was observed in lines derived from the most susceptible cultivar ‘Génesis 2375’. The most resistant lines to both diseases are expected to be valuable genetic resources in breeding for durable resistance to FHB and SR.

Genetic susceptibility to late maturity alpha-amylase (LMA) in wheat (Triticum aestivum L.) results in increased alpha-amylase activity in mature grain when cool conditions occur during late grain maturation. Farmers are forced to sell wheat grain with elevated alpha-amylase at a discount because it has an increased risk of poor end-product quality. This problem can result from either LMA or preharvest sprouting, grain germination on the mother plant when rain occurs before harvest. Whereas preharvest sprouting is a well-understood problem, little is known about the risk LMA poses to North American wheat crops. To examine this, LMA susceptibility was characterized in a panel of 251 North American hard spring wheat lines, representing ten geographical areas. It appears that there is substantial LMA susceptibility in North American wheat since only 27% of the lines showed reproducible LMA resistance following cold-induction experiments. A preliminary genome-wide association study detected six significant marker-trait associations. LMA in North American wheat may result from genetic mechanisms similar to those previously observed in Australian and International Maize and Wheat Improvement Center (CIMMYT) germplasm since two of the detected QTLs, QLMA.wsu.7B and QLMA.wsu.6B, co-localized with previously reported loci. The Reduced height (Rht) loci also influenced LMA. Elevated alpha-amylase levels were significantly associated with the presence of both wild-type and tall height, rht-B1a and rht-D1a, loci in both cold-treated and untreated samples.

The wheat industry rejects grain with unacceptably high α-amylase enzyme levels due to the risk of poor endproduct quality. There are two main causes of elevated grain α-amylase: (1) preharvest sprouting in response to rain before harvest and (2) late maturity α-amylase (LMA) induction in response to a cool temperature shock during late grain development. LMA induction was detected in a panel of 24 Northwestern US spring wheat lines. Thus, this problem previously described in Australian and U.K. varieties also exists in U.S. varieties. Because LMA induction results were highly variable using published methods, a characterization of LMA-inducing conditions was conducted in an LMA-susceptible soft white spring wheat line, WA8124. Problems with elevated α-amylase in untreated controls were reduced by raising the temperature, 25°C day/18°C night versus 20°C day/10°C night. LMA induction was not improved by colder temperatures (15°C day/4°C night) versus moderately cold temperatures (18°C day/7.5°C night or 10°C day/10°C night). While previous studies observed LMA induction by heat stress, it failed to induce LMA in WA8124. Thus, not all LMA-susceptible cultivars respond to heat. The timing of LMA susceptibility varied between two cultivars and within a single cultivar grown at slightly different temperatures. Thus, variability in LMA induction likely results from variability in the timing of the grain developmental stage during which cold shock induces LMA. Thus, it was concluded that the visual inspection of grain is needed to correctly identify LMA-sensitive spikes at the soft dough stage of grain development (Zadok's stage 85).

Salicylic acid (SA), a phytohormone, has been considered to be a key regulator mediating plant defence against pathogens. It is still vague how SA activates plant defence against herbivores such as chewing and sucking pests. Here, we used an aphid-susceptible wheat variety to investigate Sitobion avenae response to SA-induced wheat plants, and the effects of exogenous SA on some defence enzymes and phenolics in the plant immune system. In SA-treated wheat seedlings, intrinsic rate of natural increase (rm), fecundity and apterous rate of S. avenae were 0.25, 31.4 nymphs/female and 64.4%, respectively, and significantly lower than that in the controls (P < 0.05). Moreover, the increased activities of phenylalanine-ammonia-lyase, polyphenol oxidase (PPO) and peroxidase in the SA-induced seedlings obviously depended on the sampling time, whereas activities of catalase and 4-coumarate:CoA ligase were suppressed significantly at 24, 48 and 72 h in comparison with the control. Dynamic levels of p-coumaric acid at 96 h, caffeic acid at 24 and 72 h and chlorogenic acid at 24, 48 and 96 h in wheat plants were significantly upregulated by exogenous SA application. Nevertheless, only caffeic acid content was positively correlated with PPO activity in SA-treated wheat seedlings (P = 0.031). These findings indicate that exogenous SA significantly enhanced the defence of aphid-susceptible wheat variety against aphids by regulating the plant immune system, and may prove a potential application of SA in aphid control.

Cereal rye (Secale cereale L.) control in wheat (Triticum aestivum L.) can be difficult with existing selective herbicides. High phenotypic diversity within populations coupled with suboptimal herbicide application conditions leads to varying degrees of control with herbicide treatments. The following research focused on the consequence of low temperature on imazamox fate in S. cereale. A greenhouse study was conducted to determine the number of warm-temperature days required for imazamox to control S. cereale. Absorption, translocation, and metabolism of imazamox was evaluated under warm (22/18C) and cold (4/4C) temperatures to identify changes to the fate of imazamox under different environmental conditions. In greenhouse conditions, more than 5 d of warm temperature following herbicide application was required to achieve 80% S. cereale mortality. Absorption of imazamox was reduced 20% when S. cereale was subjected to cold compared with warm temperatures. Only 10% of applied imazamox was moved from the treated leaf in continuous cool temperatures compared with greater than 60% in warm conditions. In cold conditions, imazamox content increased in all tested plant parts evaluated for the duration of the study, whereas in warm conditions, imazamox concentrations decreased in root and crown tissues after 3 d. Imazamox behavior was affected more by temperature than S. cereale growth stage. Secale cereale metabolism of imazamox was reduced, but not stopped in cold temperatures. After 6 d, only a 10% difference in intact imazamox remained between temperature treatments. In cold temperatures, reduced absorption and translocation, coupled with continued metabolism, allow plants to recover from an otherwise lethal imazamox treatment.

Three herbicides, amine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid], glyphosate [N-(phosphonomethyl)glycine], and dicamba (3,6-dichloro-o-anisic acid) were applied for field bindweed (Convolvulus arvensis L.) control in grain/summerfallow or grain/legume rotations. After the first year all herbicide retreatments were made using 2,4-D amine. The 2,4-D treatment at 3.4 kg/ha gave 65% field bindweed control. Field bindweed control averaged 17% higher when the 2,4-D was applied in August rather than July. The 3.4-kg/ha rate gave 45% better field bindweed control than the 1.1 kg/ha rate. Dicamba at 6.7 kg/ha gave 90% field bindweed control and glyphosate at 4.5 kg/ha gave 86% control. Dicamba persisted in the soil for 1 to 3 yr after application and caused winter wheat (Triticum aestivum L.) and lentil (Lens culinaris Medik.) yield loss. Crop yields were highest more than 90% of the time from plots treated with 2,4-D or glyphosate.

A linear programming model was used to determine which crop rotations and weed management systems result in the highest net farm income for each of three farm sizes (120, 240, and 480 hectares) under alternative tillage systems. Test plot data for the years 1981 through 1988 from the Purdue University Agronomy Farm, which has highly productive, well-drained soils, were analyzed. Net incomes for no-till tillage systems on all farms in the model were consistently and significantly lower than incomes for moldboard and chisel plow tillage systems due to slightly lower yields and substantially higher herbicide costs. Generally, net farm incomes were slightly higher with a moldboard plow versus chisel plow tillage system. Also, as farm size increased, per hectare net incomes increased. About 80% of the time under moldboard or chisel plow tillage systems, the model chose as optimal the lowest of three herbicide application rates. A corn/soybean rotation was chosen as optimal on 56% of the farm area analyzed, versus 25% for continuous corn and 13% for a corn/soybean/wheat rotation.

In field experiments in 1981, 36 g ai/ha of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} applied to winter wheat (Triticum aestivum L. ‘Arthur’) in early spring reduced seed yield in conventional and no-till plantings of double-cropped soybeans [Glycine max (L.) ‘Essex’]. From 1982 to 1984, three rates of chlorsulfuron (9, 18, and 36 g/ha) were applied at three different times (preemergence, early winter, and early spring) to study their residual effects on double-cropped soybeans. Chlorsulfuron at 36 g/ha applied preemergence or early spring reduced soybean seed yields when averaged over the 3-yr period. Metsulfuron {2-[[[[(4-methoxy-6-methyl-1,3,5-triazine-2-yl)amino] carbonyl] amino] sulfonyl] benzoic acid} was tested at three rates (4.5, 9, and 18 g/ha) applied at three times (same as chlorsulfuron) in field studies in 1983 and 1984. Metsulfuron did not injure subsequently planted no-till soybeans.

Existing long-term cotton experiments established in 1976 with minimum and intensive herbicide programs were subdivided in 1985 and 1986 to determine the longevity of fluometuron and trifluralin soil residues after discontinuing herbicide application. In monoculture cotton, seed cotton yield increased when herbicide use was discontinued in 1985 and 1986 after 9 and 10 yr of continuous use, respectively, on a Sharkey silty clay and a Dundee silt loam soil. Yield increases coincided with reductions of fluometuron and trifluralin soil residues. Fluometuron dissipated from the Dundee silt loam soil by 10 mo after the last application but was present in the Sharkey silty clay soil at 0.20 ppmw after 28 mo. Trifluralin did not totally dissipate from either soil, and low levels were present in the Dundee (0.05 ppmw) and Sharkey (0.13 ppmw) soils 30 mo after the last application. Visual injury to fall-seeded wheat and vetch decreased as herbicide residues dissipated. Fall tillage had no significant effect on the rate of fluometuron or trifluralin dissipation from either soil but reduced seed cotton yields.

A field experiment was conducted to evaluate weed control systems in a conservation tillage rotation of grain sorghum [Sorghum bicolor (L.) Moench.] – cotton (Gossypium hirsutum L.) – wheat (Triticum aestivum L.). Herbicide systems included fall and spring/summer inputs of high and low intensity. Tillage regimes were no-till (NT) and reduced-till (RT) systems; the latter included fall primary tillage followed by spring stale seedbed planting. Both tillage systems utilized controlled traffic lanes and wide, raised beds. Effective johnsongrass [Sorghum halepense (L.) Pers. # SORHA] control required intense herbicide inputs at one or both application periods, i.e., in the fall and/or spring/summer. Grain sorghum and cotton yields for the most intense weed control system, which included high inputs in both the fall and spring/summer, were not superior to systems that included high inputs in only one of the two application periods. Seedling johnsongrass emergence occurred before spring planting in RT (but not in NT) in 2 of 3 yr, and control measures were ineffective. After 3 yr, the predominant weeds were johnsongrass and browntop panicum (Panicum fasciculatum Sw. # PANFA).

Immediately following postemergence application, similar quantities of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] were retained on the foliage of downy brome (Bromus tectorum L. # BROTE) and winter wheat (Triticum aestivum L.). Three days following treatment, more metribuzin was present on the surface of the foliage of downy brome than of winter wheat and similar quantities of metribuzin had been absorbed into the interior of the foliage of both species. Fourteen days after treatment, metribuzin had disappeared from the surfaces of the foliage of both species but more metribuzin was present in the interior of the foliage of downy brome than of winter wheat. Results from petri dish studies in the field suggested that the amount of unaltered metribuzin available for absorption by leaves was influenced primarily by volatilization and secondarily by photodecomposition. In addition, small quantities of rainfall may have washed metribuzin from leaf surfaces. In 1984, yield of winter wheat was greater in metribuzin-treated plots than in nontreated check plots.

Field experiments were conducted to determine wheat injury following clomazone application in soybeans and fallow in North Dakota. Clomazone at recommended rates generally caused 10% or less visible chlorosis in spring wheat planted 11 to 12 mo after application or winter wheat planted 11 mo after application, although greater chlorosis was observed in two of seven location/year environments. Tillage preceding wheat planting increased chlorosis from clomazone residues in some environments. Clomazone residues reduced wheat grain yield only in three of seven location/year environments and usually at application rates of 1.4 kg ai ha-1 or greater. Severe drought prevailed during the study and probably increased clomazone persistence and wheat chlorosis. Drought also may have limited expression of grain yield reductions attributable to clomazone residues.

Laboratory experiments were carried out under aseptic conditions to study the effect of nitrogen applied as ammonium nitrate at 0, 20,40,60,80 and 100 ppm (wt per vol) in either distilled H2O or modified Hoagland's solution on germination and radicle length of branched broomrape in association with growing seedlings of different crops. As nitrogen rate increased, seed germination and radicle length of branched broomrape decreased linearly in flax, lentil, pepper, tomato, and wheat in modified Hoagland's solution. Similar responses to nitrogen application were found with distilled water. The parasite's seed germination was considerably lower in the media with wheat than with other crops, and lower still in the absence of crop seedings.

Greenhouse and field experiments were conducted at the Lacombe Research Station to evaluate mixtures of sethoxydim and fluazifop on green foxtail, wild oat, wheat, and barley in canola. In both environments the two herbicides interacted on the grass species in a synergistic manner. Many of the observed responses to mixtures of sethoxydim and fluazifop were 100% greater than those expected assuming an additive interaction between the herbicides. Mixtures with at least 80 g ha-1 of sethoxydim and 80 g ha-1 of fluazifop controlled more than 90% of green foxtail, wild oat, wheat, and barley under field conditions. These experiments indicate that the sethoxydim/fluazifop mixture is both complementary and synergistic. The mixture may allow reduced herbicide application rates and therefore reduced herbicide costs and less potential for negative environmental impact.

Winter wheat grain contaminated with jointed goatgrass joints is often discounted as much as 20% by grain buyers. A mail survey to Nebraska farmers in 1984 identified jointed goatgrass as one of the ten worst weed problems in winter wheat, but a field survey to the same area in 1986 found it in less than 1% of surveyed fields. The objective of this survey was to map the geographic distribution and severity of jointed goatgrass contaminating winter wheat grain in western Nebraska. Jointed goatgrass was found in 25, 29, and 20% of all wheat samples collected in 1990, 1991, and 1992, respectively. Nebraska counties bordering Colorado were found to have the highest percentage of wheat samples contaminated with jointed goatgrass joints, ranging from 23% in Cheyenne county in 1992 to 61% in Keith county in 1991.

Flower production and pollen dispersal patterns of diclofop-methyl-susceptible and -resistant Italian ryegrass were examined to determine whether evolution of herbicide resistance could be controlled by cross-fertilization between biotypes. The susceptible and resistant ryegrass biotypes differed in timing and abundance of both ovule production and pollen release such that pollen from the susceptible plants had a much greater chance of fertilizing the resistant plant population than vice versa. Susceptible ryegrass, growing with or without wheat competition, produced more than 60% of its seeds before any pollen from resistant plants was released. In contrast, throughout the course of resistant plant seed generation, pollen from susceptible plants composed at least 30% of the total pollen load. These phenological differences, in conjunction with herbicide treatment results for third-generation ryegrass seedlings, suggest that gene flow can be used to reduce development of diclofop-methyl resistance in ryegrass populations within wheat cropping systems. In a wheat field infested with resistant ryegrass, cessation of herbicide application and sowing of a susceptible ryegrass biotype can be expected to reduce the evolution of diclofop-methyl resistance by at least 6% per year.

In the greenhouse, glyphosate [N-(phosphonomethyl)glycine] at 0.6 kg ae/ha applied directly to seeds alone or seeds on the soil surface reduced germination and shoot dry weight of common rye (Secale cereale L. ♯3 SECCE). Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) applied similarly at 0.6 kg ai/ha reduced germination and shoot dry weight of downy brome (Bromus tectorum L. ♯ BROTE) and wheat (Triticum aestivum L. ‘Daws' ♯ TRZAX). Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one] at 0.6 kg ai/ha applied to seeds, soil, or seeds and soil had very little effect on germination, but significantly reduced shoot dry weight of common rye, downy brome, wheat, and jointed goatgrass (Aegilops cylindrica Host. ♯ AEGCY). Pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] at 0.6 kg ai/ha, and propham (isopropyl carbanilate) at 3.4 kg ai/ha plus extender (p-chlorophenyl-N-methylcarbamate) at 0.4 kg ai/ha substantially reduced shoot height and dry weight of all species, regardless of application method, with pronamide completely inhibiting shoot elongation and dry-weight production in three of the four species.

Studies were conducted to determine the usefulness of HOE-39866 (HOE-00661) in chemical fallow systems on the Canadian prairies. HOE-39866 at 0.5 to 1.0 kg ai/ha controlled Russian thistle, kochia, green foxtail, wild oats, and wheat comparable to paraquat, glyphosate, and glyphosate plus the isopropylamine salt of 2,4-D. However, control of barley with HOE-39866 was unacceptable. HOE-39866 was compatible in tank mixtures with ammonium sulfate, paraquat, chlorsulfuron, and metsulfuron. Ammonium sulfate improved weed control when HOE-39866 was applied at 0.25 kg/ha but not at 0.75 kg/ha. Adding paraquat at 0.07 to 0.21 kg ai/ha to HOE-39866 improved control of grass species over HOE-39866 alone. Adding chlorsulfuron and metsulfuron to HOE-39866 provided greater initial control of certain species as well as residual control of many weeds. HOE-39866 alone or in conjunction with other herbicides is an alternative to the herbicides used in chemical fallow systems.