Tubulins are encoded by small gene families in plants. Here we report the cloning and characterization of water foxtail α-tubulin genes (AaTUA), an economically important weed. The genome of water foxtail contains TUA family consisting of at least four genes. Using degenerate primers, four partial TUA genes were isolated from the complementary DNA (cDNA) of water foxtail. Using the partial gene sequences, specific primers for each TUA gene were designed and full-length TUA cDNAs were isolated. These genes were designated as AaTUA1 to AaTUA4. The deduced amino acid sequences of AaTUA genes showed significant homology to the TUA genes of barley, corn, and Arabidopsis. The coding sequences of the AaTUA1 and AaTUA3 genes were interrupted by three introns and there were four introns in the coding regions of AaTUA2 and AaTUA4. The organ-specific expression of AaTUA genes showed that AaTUA1 and AaTUA4 were predominantly expressed in all organs examined (root, stem, young leaf, mature leaf, and panicle), whereas AaTUA2 was expressed mainly in roots and AaTUA3 was expressed in stem, root, and panicle. Abscisic acid (ABA) and gibberellic acid (GA) differentially induced the expression of AaTUA1 and AaTUA3. Moreover, trifluralin, propham, and caffeic acid induced the expression of all AaTUA genes in a dose-dependent manner except AaTUA2. This is the first report of complete sequences of AaTUA genes and the first characterization of these genes for any Alopecurus species in the literature.

Nomenclature: Water foxtail, Alopecurus aequalis Sobol Arabidopsis, Arabidopsis thaliana L.; barley, Hordeum vulgare Lcorn, Zea mays L

Laboratory studies were conducted using ¹⁴C-aminocyclopyrachlor (DPX-MAT28) and its ¹⁴C-methyl ester formulation (DPX-KJM44) to (1) determine the adjuvants' effects on absorption, (2) compare the absorption and translocation of aminocyclopyrachlor free acid with the methyl ester, and (3) determine the rate at which aminocyclopyrachlor-methyl ester is metabolized to the free acid in Canada thistle. Canada thistle plants were grown from root cuttings and treated in the rosette growth stage. The effect of different adjuvants on absorption was determined by treating individual leaves with formulated herbicide plus ¹⁴C-herbicide alone or with methylated seed oil (MSO), crop oil concentrate, or nonionic surfactant with and without urea ammonium nitrate and ammonium sulfate. Plants were harvested 96 h after treatment (HAT). For absorption and translocation experiments, plants were oversprayed with aminocyclopyrachlor or its methyl ester at a rate of 0.14 kg ae ha⁻¹ in combination with 1% MSO. Formulated herbicide plus ¹⁴C-herbicide was then applied to a protected leaf, and plants were harvested 24 to 192 HAT. Plants were harvested and radioactivity was determined in the treated leaf and in aboveground and belowground tissues. Metabolism of aminocyclopyrachlor-methyl ester to the free acid was determined 2, 6, and 24 HAT. All aboveground biomass was analyzed by high-performance liquid chromatography to establish the ratio of methyl ester to free acid. MSO applied with either herbicide formulation resulted in the highest absorption compared with no surfactant. Significantly greater aminocyclopyrachlor-methyl ester was absorbed, compared with the free acid, which was reflected in the greater aboveground translocation for the methyl ester. Both formulations had similar amounts of translocation to the roots, with 8.6% (SE ± 3.3) for the methyl ester compared with 6.2% (SE ± 2.5) for the free acid. Approximately 80% of the methyl ester was converted to the free acid at 6 HAT. Based on this conversion rate, aminocyclopyrachlor translocated as the free acid in Canada thistle.

Nomenclature: Aminocyclopyrachlor (6-amino-5-chloro-2-cyclopropyl-4-pyrimidinecarboxylic acid), aminocyclopyrachlor-methyl ester (6-amino-5-chloro-2-cyclopropyl-4-pyrimidin methyl ester) Canada thistle, Cirsium arvense L. CIRAR

Aminocyclopyrachlor, a newly discovered synthetic auxin herbicide, and its methyl ester, appear to control a number of perennial broadleaf weeds. The potential volatility of this new herbicide and its methyl ester were determined under laboratory conditions and were also compared to dicamba and aminopyralid with the use of enclosed chamber and open-air plant bioassays. Bioassays consisting of visual estimates of epinastic responses and kidney bean and soybean leaf-width measurements were developed to measure vapor release from glass and plastic. Vapor release of aminocyclopyrachlor from glass surfaces was undetectable under laboratory conditions, and no phytotoxic responses were observed when plants were exposed to vapors emanating from various surfaces. Results were similar to those of aminopyralid, indicating the risk of plant injury from vapor movement of aminocyclopyrachlor and aminopyralid was very low. When combined with 1% methylated seed oil, vapor release of aminocyclopyrachlor-methyl ester reached 86% 192 h after application to glass surfaces. Phytotoxic responses of plants exposed to vapors emanating from various surfaces treated with aminocyclopyrachlor-methyl ester were similar to responses to dicamba under enclosed incubation conditions, but were less in outdoor, open-air environments. Studies are needed to understand better the risk of injury to nontarget plants due to vapor movement of aminocyclopyrachlor-methyl ester under field applications.

Nomenclature: Aminocyclopyrachlor aminopyralid kidney bean, Phaseolus vulgaris, ‘Green potted bush’ soybean, Glycine max (L.) Merr. ‘Pioneer 94B53’

The evolution of glyphosate resistance in weedy species places an environmentally benign herbicide in peril. The first report of a dicot plant with evolved glyphosate resistance was horseweed, which occurred in 2001. Since then, several species have evolved glyphosate resistance and genomic information about nontarget resistance mechanisms in any of them ranges from none to little. Here, we report a study combining iGentifier transcriptome analysis, cDNA sequencing, and a heterologous microarray analysis to explore potential molecular and transcriptomic mechanisms of nontarget glyphosate resistance of horseweed. The results indicate that similar molecular mechanisms might exist for nontarget herbicide resistance across multiple resistant plants from different locations, even though resistance among these resistant plants likely evolved independently and available evidence suggests resistance has evolved at least four separate times. In addition, both the microarray and sequence analyses identified non–target-site resistance candidate genes for follow-on functional genomics analysis.

Nomenclature: Glyphosate, horseweed, Conyza canadensis (L.) Cronq. ERICA

Old World climbing fern is one of the most invasive plants in natural areas of central and southern Florida. The fern spreads across the landscape by wind-blown spores and invades isolated and undisturbed habitats such as interior portions of the Florida Everglades. Land managers in Florida have reported that multiple herbicide treatments are required to control the fern, which could indicate that herbicides do not translocate throughout the plant in long-established populations. We conducted a greenhouse study to determine the absorption and translocation patterns in Old World climbing fern using the three herbicides most commonly used for management of this plant by land managers in Florida. Using ¹⁴C-labeled herbicides, we evaluated absorption and translocation of glyphosate (2.25 kg ai ha⁻¹), metsulfuron (0.10 kg ai ha⁻¹), and triclopyr (1.68 kg ai ha⁻¹) in Old World climbing fern using five different application scenarios (cut-and-spray, basal spray, 25% foliar spray, 50% foliar spray, and 100% foliar spray). Triclopyr was absorbed to the greatest extent (60.3%) of applied radioactive compounds compared to glyphosate (31.2%) and metsulfuron (19.8%). The majority of radioactivity remained in treated leaves for all herbicides with only small percentages of the absorbed radioactivity being detected in other plant parts. All three herbicides translocated acropetally and basipitally to some extent. Radioactivity, for the most part, translocated evenly throughout the plants but the greatest amount of radioactivity derived from triclopyr occurred in rhizomes when the cut-and-spray and basal applications were used. The radioactivity in rhizomes derived from glyphosate was greater in those treated using cut-and-spray. Based on autoradiographs, there was limited horizontal movement of any herbicide in the rhizomes of Old World climbing fern which could explain why resprouts are observed several weeks following treatment.

Nomenclature: Glyphosate, metsulfuron; triclopyr; Old World climbing fern, Lygodium microphyllum (Cav.) R. Br

Pigweed is an increasingly aggressive weed in semiarid environments such as Mediterranean areas, and in general the control of all Amaranthus species is becoming more and more difficult. Increasing pigweed aggressiveness could be a result of its ability to keep a high water use efficiency under drought conditions. An experiment was conducted to study the effect of water stress on the photosynthetic capacity, growth, and leaf water potential of pigweed at the field level and assess if this species, as a model for C₄ weeds, is CO₂-saturated at the current level of atmospheric CO₂ in a Mediterranean area. Pigweed was studied within a naturally occurring weed population in a bell pepper field in southern Italy where a rain-fed treatment (V0) was compared to a fully irrigated one (V100) corresponding to the restoration of 100% of the maximum crop water evapotranspiration. Soil water content was measured periodically, and net assimilation rate, stomatal conductance, transpiration rate, and intercellular CO₂ concentration were determined on pigweed leaves. Photosynthetic rates of 37.6 µmol m⁻² s⁻¹ in V100 and 13.9 µmol m⁻² s⁻¹ in V0 were recorded, with higher transpiration rates in V100; consequently stomatal conductance was significantly lower in rain-fed conditions (0.08 mol m⁻² s⁻¹⁾) compared to the irrigated treatment (0.30 mol m⁻² s⁻¹). Photosynthesis in pigweed is not completely CO₂-saturated at the current atmospheric CO₂ level in the Mediterranean area and this could affect competition and increase of aggressiveness toward crops at the actual CO₂ atmospheric concentration in agro-ecosystems. This occurs because unlike other C₄ crops already saturated for CO₂, weeds that are not CO₂-saturated will remain CO₂-sensitive to higher ambient CO₂ levels. Thus, when they are grown in mixed stands where competition occurs, they can still suppress the slower-growing species.

Nomenclature: Redroot pigweed, Amaranthus retroflexus L. AMARE, bell pepper, Capsicum annuum L. ‘Peppone’

Junglerice is one of the most serious grass weeds of rice in the tropics. Greenhouse studies were conducted to evaluate growth and reproduction of junglerice in response to water stress. Plant height, biomass, and seed production of junglerice grown alone were reduced with increasing water stress. However, most stressed plants (irrigated at 12.5% of field capacity) still produced considerable biomass (8.5 g plant⁻¹) and seeds (>1,600 seeds plant⁻¹). When junglerice and rice were grown together under water-stressed condition, junglerice was taller than rice. The junglerice-to-rice biomass ratio also increased from 4.7 at 100% of field capacity to 7.6 at 12.5% of field capacity, indicating the greater junglerice vigor in water-stress conditions. In another study, the influence of the duration of water stress at intervals between 3 and 15 d on growth and seed production of junglerice was evaluated. Plant height, biomass, and seed production decreased with increasing water-stress duration. However, the weed produced an average of 400 seeds plant⁻¹ in the most stressed treatment (i.e., when irrigation was applied at 15-d intervals). Water-stressed treatments did not affect germination of junglerice seeds in the laboratory. Growth and seed production of junglerice at all moisture levels ensures survival of the population in an unpredictable environment and contributes to the weedy nature of this species. The joint effect of enhanced weed competition and drought stress could severely harm crop yield; therefore, it is important to control such weeds in the early stages of crops and save stored moisture for the crops.

Nomenclature: Junglerice, Echinochloa colona (L.) Link ECHCO, rice, Oryza sativa L

Knowledge of the germination requirements of wild radish will help in determining the favorable conditions for germination and emergence and allow better management of this weed. Experiments were conducted during 2005 to 2006 and 2006 to 2007 to evaluate wild radish temperature and light requirements over a 12-mo period beginning in July on seeds placed on the soil surface and at a 10-cm depth. Germination response was influenced by temperature, light, duration of burial, and burial depth. Freshly harvested seeds (July) had no more than 18% germination whereas seeds allowed to after-ripen in the field for 3 to 6 mo (October to January) had up to 40% germination. The germination of wild radish retrieved from the soil surface was 1.2 to 1.5 times greater at alternating temperatures (2.5/17.5, 7.5/22.5, and 12.5/27.5 C) than at constant temperatures (10, 15, and 20 C) at 0, 3, and 6 mo after maturation. The light requirement for germination varied by time of year with no differences in germination between light and dark conditions for freshly harvested seeds. Far-red light inhibited germination of wild radish, indicating that wild radish may become sensitive to light following an after-ripening period.

Nomenclature: Wild radish, Raphanus raphanistrum L. RAPRA

The spread of buffalobur in China poses a serious threat to existing ecosystems, and control and eradication of this species have become increasingly important. Studies were carried out to ascertain the seed production, morphological characterization, dormancy behavior, and methods for breaking dormancy of buffalobur. The results showed that a single buffalobur plant could produce 1,600 to 43,800 seeds with an average weight of 3.0 mg. Average seed length, width, and thickness were 2.5, 2.0, and 1.0 mm, respectively. Newly ripened buffalobur seeds were innately dormant and exhibited combinational dormancy, which involves a hard seed coat (physical dormancy, PY), a partial dormant embryo (physiological dormancy, PD), and a dark requirement to germinate. PY of buffalobur seeds could be broken by dehusking or acid scarification by 14 M H₂SO₄ for 15 min, with germination rates of 55 or 50%, respectively. PD was effectively broken by KNO₃ or gibberellic acid (GA₃). The optimum concentration for KNO₃ was between 20 and 40 mM, which resulted in over 70% seed germination. When presoaked with GA₃ at 30 C in dark for 24 h, maximum germination (> 98%) was obtained at 2.4 mM, the corresponding germination speed (85%) and germination index (16) were also highest at this concentration. Synergistic effects were observed in seed germination when H₂SO₄ and GA₃ were combined. The most rapid and effective combination in breaking dormancy was when the seeds were immersed in H₂SO₄ (14 M) for 20 min and presoaked with 2.4 mM GA₃ for 24 h. Germination index for this combination was over 35, and 95% of the seeds germinated within 7 d. Knowledge gained in this study will be useful in increasing germination of buffalobur and facilitating further laboratory studies.

Nomenclature: Buffalobur, Solanum rostratum Dunal SOLCU

Experiments were conducted in 2006 to 2008 to study growth, phenology, and competitive ability of glyphosate-resistant (GR) and -susceptible (GS) biotypes of horseweeds from San Joaquin Valley (SJV), CA. When grown alone, in pots, the GR horseweeds consistently developed more rapidly than the GS weeds, as evidenced by their earlier bolting, flowering, and seed set; the GR horseweeds set seeds nearly 25 d (approximately 190 fewer growing degree days) sooner than the GS horseweed. At seed set, the relatively slow-developing GS horseweeds had amassed 40% more shoot dry matter than the GR weeds at the same phenological stage, but neither biotype was consistently more fecund than the other. Although the GR biotype had lower shoot dry mass than the GS biotype when grown alone, in mixed populations under increasing levels of competition (in a replacement series design) and limited resources (mainly moisture), the GR weeds were not only taller, but also accumulated more dry matter than the GS weeds. Thus, the GR biotype was more competitive than the GS biotype, particularly when grown at high densities and under moisture-deficit stress. Therefore, under California conditions there is no apparent fitness penalty for this particular GR horseweed biotype, and it is likely to persist in the environment and outcompete the GS biotypes regardless of further glyphosate selection pressure. If so, this biotype of GR horseweed is likely to become increasingly common in the SJV until effective management strategies are developed and adopted.

Nomenclature: Horseweed, Conyza canadensis (L.) Cronq. ERICA

We conducted a greenhouse study to examine the effects of different habitat conditions and environmental resources on the growth rates of crimson fountaingrass, an invasive, alien, perennial grass in South Africa. To help understand the factors promoting the spread of this emergent alien grass, we investigated the effects of temperature regimes, nutrient and moisture addition, and soil type on seedling growth rates and biomass allocation. Our results suggest that crimson fountaingrass seedlings do not tolerate drought because they died within 1 mo without water. Additional nutrients and extra water increased seedling growth rates throughout the study period. Higher temperatures with extra moisture increased seedling growth rates and the development of belowground biomass throughout the study period. This study demonstrates the importance of available environmental resources and their interaction with some habitat conditions in promoting crimson fountaingrass growth. We suggest that soil moisture and nutrient availability are critical factors affecting successful establishment of crimson fountaingrass in arid environments. Managers should target seedlings for removal following precipitation and in areas of nutrient enrichment, such as near rivers and at road–river crossings.

Nomenclature: Crimson fountaingrass, Pennisetum setaceum (Forsk.) Chiov. PESSA

Common groundsel adapts readily to new environments and selection pressures and has been variably described as both a winter and summer annual. We characterized germination response to temperature in seeds from populations occurring at six sites along a 700-km north–south transect (Kentucky to Michigan). Seeds were collected in 2000 and 2002 from randomly selected plants (350 to 400), at each sampling site. Two germination patterns were observed: (1) seeds from the southern locations averaged 80 to 90% germination across the range of 5 to 25 C; and (2) seeds from northern locations had reduced germination when incubation temperatures were close to 5 or 25 C. When seed from all locations were grown in a common environment (14/10-h thermoperiod of 22/18 C), their progeny had a germination response that was similar across the temperature gradient, regardless of original location, suggesting germination of the parent seed was due to maternal environmental effects. In a subsequent experiment, common groundsel was grown in growth chambers with warm long days (22/15 C and 16 h of light), warm short days (8 h of light), cold long days (15/8 C and 16 h of light), and cold short days. Eighty percent of seeds from the warm environments germinated across the range from 5 to 25 C indicating that these maternal conditions had produced nondormant seeds. In contrast, 20% or fewer of the seeds from plants in the cold chambers germinated regardless of temperature, suggesting that dormancy had been induced by the cool maternal environment. Results also indicated that signaling of maternal environment varied with inflorescence development stages, meaning the earlier the inflorescences are exposed to cold conditions, the lower the percent germination in F₁ seeds. Preventing seed maturation on common groundsel growing under cool conditions may reduce the formation of a persistent seed bank.

Nomenclature: Common groundsel, Senecio vulgaris L. SENVU

Experiments were conducted to determine the amount of time required for waterhemp to produce mature seeds after pollination. Female waterhemp plants were pollinated over a 24-h time period and then isolated from males. Two branches, each containing at least 500 flowers, were harvested from each female at the time of the initial pollination, designated as 0 d after pollination (DAP), as well as at multiple other times after pollination up to 62 DAP. One branch from each harvest was stored at 30 C for 48 h, while the other branch was stored at −20 C for 48 h. Branches were then stored at room temperature until all harvests were complete, at which time seeds from each branch at each time after pollination were collected, weighed, and stratified. Germination tests were then conducted to determine the time at which seeds become viable after pollination. Seeds that had not germinated by the end of the germination tests were subjected to tetrazolium testing for viability. Germination tests were also conducted on nonstratified seeds to investigate changes in seed dormancy that were expected to occur over the amount of time the seeds were allowed to remain on the plants. Seeds stored initially at 30 C postharvest became viable 7 to 9 DAP, whereas seeds stored initially at −20 C postharvest did not become mature until 11 DAP. Seed coat color was white soon after pollination and became dark brown to nearly black by 12 DAP, and seed weight increased until 12 DAP. Tetrazolium tests for seed viability correlated well with the germination tests. Germination tests on nonstratified seeds indicated that dormancy level was initially high in the population used, but began to decrease between 15 and 30 DAP. Results of this study have implications both for waterhemp management and research.

Nomenclature: Waterhemp, Amaranthus tuberculatus (Moq.) Sauer AMATU,

Crop rows oriented at a right angle to sunlight direction (i.e., east–west within the winter cropping system in Western Australia) may suppress weed growth through greater shading of weeds in the interrow spaces. This was investigated in the districts of Merredin and Beverley, Western Australian (latitudes of 31° and 32°S) from 2002 to 2005 (four trials). Winter grain crops (wheat, barley, canola, lupines, and field peas) were sown in an east–west or north–south orientation. Within wheat and barley crops oriented east–west, weed biomass (averaged throughout all trials) was reduced by 51 and 37%, and grain yield increased by 24 and 26% (compared with crops oriented north–south). This reduction in weed biomass and increase in crop yield likely resulted from the increased light (photosynthetically active radiation) interception by crops oriented east–west (i.e., light interception by the crop canopy as opposed to the weed canopy was 28 and 18% greater in wheat and barley crops oriented east–west, compared with north–south crops). There was no consistent effect of crop row orientation in the canola, field pea, and lupine crops. It appears that manipulation of crop row orientation in wheat and barley is a useful weed-control technique that has few negative effects on the farming system (i.e., does not cost anything to implement and is more environmentally friendly than chemical weed control).

Nomenclature: Barley, Hordeum vulgare L, canola, Brassica napus L, field pea, Pisum sativum L, lupine, Lupinus angustifolius L, wheat, Triticum aestivum L