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Southern crabgrass [Digitaria ciliaris (Retz.) Koeler] is an annual grass weed that commonly infests turfgrass, roadsides, wastelands, and cropping systems throughout the southeastern United States. Two biotypes of D. ciliaris (R1 and R2) with known resistance to cyclohexanediones (DIMs) and aryloxyphenoxypropionates (FOPs) previously collected from sod production fields in Georgia were compared with a separate susceptible biotype (S) collected from Alabama for the responses to pinoxaden and to explore the possible mechanisms of resistance. Increasing rates of pinoxaden (0.1 to 23.5 kg ha−1) were evaluated for control of R1, R2, and S. The resistant biotypes, R1 and R2, were resistant to pinoxaden relative to S. The S biotype was completely controlled at rates of 11.8 and 23.5 kg ha−1, resulting in no aboveground biomass at 14 d after treatment. Pinoxaden rates at which tiller length and aboveground biomass would be reduced 50% (I50) and 90% (I90) for R1, R2, and S ranged from 7.2 to 13.2 kg ha−1, 6.9 to 8.6 kg ha−1, and 0.7 to 2.1 kg ha−1, respectively, for tiller length, and 7.7 to 10.2 kg ha−1, 7.2 to 7.9 kg ha−1, and 1.6 to 2.3 kg ha−1, respectively, for aboveground biomass. Prior selection pressure from DIM and FOP herbicides could result in the evolution of D. ciliaris cross-resistance to pinoxaden herbicides. Amplification of the carboxyl-transferase domain of the plastidic ACCase by standard PCR identified a point mutation resulting in an Ile-1781-Leu amino acid substitution only for the resistant biotype, R1. Further cloning of PCR product surrounding the 1781 region yielded two distinct ACCase gene sequences, Ile-1781 and Leu-1781. The amino acid substitution, Ile-1781-Leu in both resistant biotypes (R1 and R2), however, was revealed by next-generation sequencing of RNA using Illumina platform. A point mutation in the Ile-1781 codon leading to herbicide insensitivity in the ACCase enzyme has been previously reported in other grass species. Our research confirms that the Ile-1781-Leu substitution is present in pinoxaden-resistant D. ciliaris.
Bermudagrass is a major forage species throughout Georgia and the Southeast. An essential part of achieving high-yielding, top-quality forages is proper weed control. Indaziflam is a residual herbicide that controls many broadleaf and grass species by inhibiting cellulose biosynthesis. Research conducted in Tift and Colquitt counties in Georgia determined optimal PRE rates for indaziflam for bermudagrass forage production. Treatments applied at spring greenup of established ‘Alicia’ bermudagrass included indaziflam at 47, 77, 155, or 234 g ai ha−1 PRE, pendimethalin at 4,480 g ha−1 PRE, a split application of indaziflam at 47 g ha−1 PRE followed by the same rate applied POST after the first cutting, and a nontreated control (seven treatments in all). Forages were machine harvested three times each year for each location beginning at least 47 d after treatment (DAT), with final cuttings up to 168 DAT. For all treatments, fresh- and dry-weight yields at each harvest and totals for the season did not differ from the nontreated control. Indaziflam at 155 and 234 g ha−1 did cause minor stunting at 44 DAT, but this was transient and not observed at the second harvest. Indaziflam applied PRE has the potential to provide residual control of troublesome weeds in bermudagrass forage and hay production, with ephemeral stunting at the recommended application rates.
We offer a friendly criticism of May's fantastic book on moral reasoning: It is overly charitable to the argument that moral disagreement undermines moral knowledge. To highlight the role that reasoning quality plays in moral judgments, we review literature that he did not mention showing that individual differences in intelligence and cognitive reflection explain much of moral disagreement. The burden is on skeptics of moral knowledge to show that moral disagreement arises from non-rational origins.
Fine fescues (Festuca spp.) are cool-season grasses used in low-maintenance turf areas. Mesotrione is a PRE and early-POST herbicide used during establishment of most cool-season turfgrasses, excluding fine fescues. Currently, efforts are being made to breed for increased tolerance to mesotrione in fine fescues to enhance weed control during establishment. This study was conducted to evaluate the association of foliar and root uptake of [14C]mesotrione with the tolerance of three lines each of Chewings fescue [Festuca rubra ssp. commutata Gaudin; syn. F. rubra ssp. fallax (Thuill.) Nyman], hard fescue [Festuca trachyphylla (Hack.) Hack.], and strong creeping red fescue (Festuca rubra L. ssp. rubra) lines. From a rate-titration experiment, the hierarchical rank of species for mesotrione tolerance from highest to lowest was: hard > Chewings > strong creeping red fescue. The hierarchical rank of species for foliar uptake from highest to lowest was: Chewings > strong creeping red > hard fescue. Translocation of foliar-absorbed 14C was not associated with differential tolerance levels of the three species. Root absorption was comparable among species, but differences between lines were detected within the species. The most susceptible lines of Chewings and strong creeping red fescue exhibited greater root uptake than lines with greater tolerance. Hard fescue translocated the least amount of root-absorbed radioactivity to shoots, while Chewings and strong creeping red fescues were comparable.
An annual bluegrass (Poa annua L.) biotype with limited susceptibility to POST flumioxazin applications was identified in Georgia. The objectives of this research were to quantify tolerance levels of this biotype (R-biotype) to protoporphyrinogen oxidase (PPO) inhibitors and characterize physiological responses to flumioxazin. In dose–response experiments on 3- to 5-tiller plants, flumioxazin and sulfentrazone rates required to reduce dry-shoot biomass 50% from the nontreated were >14.5 and 10.4 times greater for the R-biotype, as compared with a susceptible (S)-biotype, respectively. Establishment of the R-biotype from seed was completely controlled by PRE applications of flumioxazin and oxadiazon, similar to the S-biotype. Tank mixtures of chlorpyrifos with flumioxazin did not enhance biomass reductions of the R-biotype, suggesting that tolerance levels may not be related to cytochrome P450–associated metabolism. In laboratory experiments, the R-biotype averaged 27% less electrolyte leakage, as compared with the S-biotype, after flumioxazin treatments. Lipid peroxidation in the R-biotype, as measured by malondialdehyde levels, averaged 25% less than the S-biotype at 72 h after broadcast flumioxazin treatments at 280 and 560 g ha−1. The tolerance to POST applications of PPO inhibitors in this P. annua biotype is associated with less lipid peroxidation and electrolyte leakage as compared with the S-biotype. These biochemical differences in biotypes may contribute to erratic levels of POST control from flumioxazin and could contribute to PPO-inhibitor resistance.
Tall fescue is susceptible to injury from many acetolactate synthase (ALS) inhibitors used for broadleaf weed control in turfgrass. Florasulam is an ALS inhibitor that selectively controls broadleaf weeds in tall fescue, but the mechanisms for selectivity are not well understood. The objective of this research was to evaluate the physiological basis of tall fescue tolerance to florasulam. In greenhouse experiments, florasulam rates required to injure tall fescue 20% (I20) and white clover 80% (I80) measured 320 and 65 g ai ha–1, respectively. The I20 and I80 values of another ALS inhibitor, flucarbazone, on these species measured 33 and 275 g ai ha–1, respectively. In laboratory experiments, the time required to reach 50% foliar uptake for 14C-florasulam and 14C-flucarbazone measured 23 and 62 h for white clover, respectively, and >72 h for both herbicides in tall fescue. The half-lives of florasulam and flucarbazone in tall fescue were 15 and 40 h, respectively, whereas the half-life in white clover was >72 h for both herbicides. The concentrations of florasulam and flucarbazone required to inhibit ALS enzymes 50% in excised leaves of tall fescue measured >1,000 and 32 μM, respectively. The selectivity of florasulam for white clover control in tall fescue is associated with differential levels of absorption and metabolism between species. Tall fescue has faster metabolism and less ALS enzyme inhibition from florasulam as compared to a more injurious ALS inhibitor, flucarbazone, which contributes to the differential tolerance levels between these herbicides.
Leptin is synthesised and secreted from adipocytes into the blood stream and transported to the brain, where it acts to cause a release of factors which can reduce food intake (Houseknecht et al., 1998). There are two murine mutations of the recessive gene coding for leptin which are associated with obesity. The Lepob allele determines synthesis and secretion of leptin, while the Lepdb allele determines responsiveness to leptin. In the Edinburgh lean growth experiment in pigs, selection for high and low daily food intake (DFI) has been practiced for seven generations in a Large White herd, which provides the experimental resource to determine if the correlated response in fat deposition is consistent with insufficient leptin production or with insensitivity to leptin.
An in vivo procedure to determine nutrient requirements for growing pigs would have substantial cost advantages over serial slaughter and furthermore repeated measurements would allow estimation of protein requirements at each stage of growth. Serum urea concentration (Urea) has been proposed as a candidate indicator of protein requirement as over-supply of protein will increase Urea (Chen et al., 1995). The study estimated genetic variation in Urea at different stages of performance test and the relationships between Urea and performance traits.
Insulin-like growth factor-1 has been positively associated components of growth in pigs, such as protein deposition. Therefore, serum insulin-like growth factor-1 concentration (IGF-1) was measured in lines of pigs divergently selected for daily food intake (DFI) or for efficient lean growth rate (LGS) to determine if there was a non-zero genetic association between IGF-1 and the selection criteria. If a genetic association did exist, then IGF-1 could be used as a physiological predictor of genetic merit in a breeding programme. The presence of a major gene effect on IGF-1 was also examined in the study.
Two populations of southern crabgrass identified in Georgia turfgrass were suspected to be resistant to sethoxydim. The objectives of this research were to evaluate the resistance levels of these biotypes to acetyl-CoA carboxylase (ACCase) inhibitors and alternative herbicides for control. From dose response experiments, the sethoxydim rate required to reduce shoot biomass 50% from the nontreated measured >64-times greater for both resistant (R) biotypes compared to the susceptible (S) biotype. Both R biotypes were cross-resistant to fenoxaprop and fluazifop. Clethodim at 290 gaiha−1 reduced dry shoot biomass of the R biotypes and the S biotype to 47 and 21% of the nontreated, respectively. The R biotypes were equally susceptible to MSMA at 2240 g ai ha−1, quinclorac at 840 g ai ha−1, and topramezone at 37 g ai ha−1 as compared to the S biotype. Sethoxydim at 315 and 945 g ha−1 provided <20% control of the southern crabgrass populations in four field experiments. However, clethodim and topramezone provided 83% and 76% control at 4 wks after treatment, respectively. These southern crabgrass biotypes are resistant to sethoxydim and aryloxyphenoxypropionate herbicides. Although the R biotypes were less susceptible to clethodim than the S biotype, treatments provided acceptable control in the field. This is the first report of ACCase-resistant southern crabgrass in the United States.
A biotype of annual bluegrass with suspected resistance to pronamide was collected from a golf course in Georgia. The objectives of this research were to determine the level of resistance to pronamide and the mechanisms associated with resistance. From POST applications, the pronamide rate that reduced shoot biomass 50% from the nontreated bluegrass measured>10 times higher for the resistant (R) biotype as compared with susceptible (S) biotypes. The R biotype was not controlled by PRE applications of dithiopyr or prodiamine, but was controlled >92% by PRE applications of pronamide at 0.56 and 1.68 kg ha−1. Mature plants (3- to 5-tiller) of the R biotype absorbed 32% less [14C]pronamide than the S biotype after 72 h in hydroponic culture and accumulated 39% less radioactivity per gram basis of dry shoot mass. The R biotype metabolized [14C]pronamide similar to the S biotype, averaging 16% of the extracted radioactivity. The resistance to POST pronamide applications in the R biotype is associated with reduced absorption and translocation compared with the S biotype.
Annual bluegrass is a weed species in turfgrass environments known for exhibiting resistance to multiple herbicide modes of action, including photosystem II (PSII) inhibitors. To evaluate populations of annual bluegrass for susceptibility to PSII inhibitors of varied chemistries, populations were treated with herbicides from triazolinone, triazine, and substituted urea families: amicarbazone, atrazine, and diuron, respectively. Sequencing of the psbA gene confirmed the presence of a Ser264 to Gly amino acid substitution within populations that exhibited resistance to both atrazine and amicarbazone. A single biotype, DR3, which lacked any previously reported psbA gene point mutation, exhibited resistance to diuron, atrazine, and amicarbazone. DR3 had a significantly lower rate of absorption and translocation of atrazine and had enhanced atrazine metabolism when compared with both the Ser264 to Gly resistant mutant and susceptible biotypes. We thus report possible nontarget mechanisms of resistance to PSII-inhibiting herbicides in annual bluegrass.
A goosegrass biotype with suspected resistance to acetyl-CoA carboxylase
(ACCase) inhibitors was identified in Georgia. The objectives of this
research were to evaluate the resistance level of this biotype to ACCase
inhibitors, efficacy of various herbicide mechanisms of action for control,
and the physiological and molecular basis of resistance. In greenhouse
experiments, the rate of diclofop-methyl that reduced dry shoot biomass 50%
(SR50) from the nontreated for the resistant (R) and
susceptible (S) biotypes measured 4,100 and 221 g ai ha−1,
respectively. The SR50 for sethoxydim measured 615 and 143 g ai
ha−1 for the R and S biotype, respectively. The R biotype was
cross resistant to clethodim, fenoxaprop, and fluazifop. The R and S
biotypes were equally susceptible to foramsulfuron, glyphosate, monosodium
methylarsenate (MSMA), and topramezone. In laboratory experiments, the two
biotypes had similar foliar absorption of 14C-diclofop-methyl.
Both biotypes metabolized 14C-diclofop-methyl to diclofop acid
and a polar conjugate, but the R biotype averaged ∼2 times greater
metabolism than the S biotype. Gene sequencing revealed an Asp-2078-Gly
substitution in the ACCase of the R biotype that has previously conferred
resistance to ACCase inhibitors. A second mutation was identified in the R
biotype that yielded a Thr-1805-Ser substitution that has been previously
reported, but is not associated with ACCase resistance in other species.
Thus, the Asp-2078-Gly substitution is the basis for resistance to ACCase
inhibitors for the R biotype. This is the first report of ACCase-inhibitor
resistance in goosegrass from the United States and from a turfgrass
Doveweed is a summer annual that is difficult to control in turfgrass.
Photosystem II inhibitors have the potential to control doveweed, but
research is limited on the efficacy of these herbicides. The objectives of
this research were to evaluate (1) the differential tolerance levels of
doveweed to atrazine and simazine, (2) the influence of application
placement and rate on herbicide efficacy, and (3) uptake and metabolism of
these herbicides in doveweed. In greenhouse experiments, the time required
to injure doveweed 50% was three to five times faster for atrazine than
simazine. Simazine soil or foliar + soil application reduced doveweed
biomass 77% from the nontreated, but foliar-only treatments reduced biomass
51%. Application placements for atrazine equally reduced shoot biomass 96%
from the nontreated. In a dose–response experiment, atrazine and simazine
required ≤ 1.8 kg ha−1 and ≥ 5.1 kg ha−1 to injure
doveweed 50% from 8 to 16 d after treatment (DAT), respectively. Doveweed
required 79% less atrazine to reduce biomass 50% from the nontreated
compared with simazine. In laboratory experiments, doveweed had similar root
absorption levels of 14C-atrazine and 14C-simazine.
Metabolism of both herbicides linearly increased from 1 to 7 DAT, but parent
herbicide levels averaged 39 and 25% of the extracted radioactivity from
14C-atrazine and 14C-simazine, respectively.
Doveweed metabolized 14C-simazine to three major metabolites,
including hydroxysimazine, that each ranged from 24 to 29% of the extracted
radioactivity. Hydroxyatrazine was the only major metabolite (> 10% of
total 14C extracted) of 14C-atrazine. Overall,
doveweed has slower metabolism of atrazine compared with simazine and is the
basis for differential tolerance levels to these herbicides.
Mesotrione provides PRE and early POST control of annual bluegrass during Kentucky bluegrass establishment from seed, but applications do not effectively control multitiller plants. The physiological effects of growth stage on efficacy and the basis of mesotrione selectivity between species is not well understood. The objectives of this research were to evaluate mesotrione behavior in these species at three growth stages: pretiller (3 to 5 leaves), 1-tiller, and multitiller (5 to 7 tillers). In greenhouse experiments, a single mesotrione application at 280 g ai ha−1 injured pretiller, 1-tiller, and multitiller annual bluegrass 54, 33, and 11% at 4 wk after initial treatment (WAIT), respectively. A sequential application of mesotrione increased injury to pretiller and 1-tiller annual bluegrass by 20 and 17% from a single treatment, respectively. Sequential mesotrione applications caused at least 14% injury to multitiller annual bluegrass and Kentucky bluegrass at all growth stages and did not reduce tillering compared to the nontreated. Annual bluegrass absorbed 34% more root-applied 14C-mesotrione than Kentucky bluegrass in hydroponic culture, but relative differences (Bq g−1) among growth stages were not detected for both species. Averaged across growth stages, annual and Kentucky bluegrass absorbed 31 and 35% of the applied radioactivity after foliar treatments, respectively. However, averaged across species, multitiller plants metabolized approximately two times more 14C-mesotrione than pretiller and 1-tiller plants. Overall, the selectivity of mesotrione for annual bluegrass control during Kentucky bluegrass establishment results from differential levels of root absorption. Mesotrione has limited efficacy for controlling multitiller annual bluegrass due to enhanced degradation compared to pretiller and 1-tiller plants.
Metsulfuron is used for POST control of spotted spurge in many warm-season
turfgrasses. A suspected resistant (R) biotype of spotted spurge was
collected from turfgrass in Georgia with a history of exclusive metsulfuron
use. Research was conducted to evaluate the resistance level of this biotype
to metsulfuron, efficacy of other mechanisms of action for control, and the
molecular basis for resistance. Compared with a susceptible (S) biotype, the
R biotype required >90 and >135 times greater metsulfuron rates to
reach 50% injury and reduce biomass 50% from the nontreated, respectively.
The R biotype was also resistant to trifloxysulfuron but was injured
equivalent to the S biotype from dicamba, glyphosate, and triclopyr. Gene
sequencing of the R biotype revealed a Trp574 to Leu substitution
that has conferred resistance to acetolactate synthase (ALS) inhibitors in
previous research. This is the first report of ALS resistance in spotted
spurge. More importantly, this is the first report of a herbicide-resistant
broadleaf weed from a turfgrass system in the United States.
Turfgrass managers can reduce foliar bleaching of smooth crabgrass from mesotrione by tank-mixing triclopyr ester with applications. These tank mixtures also have potential to enhance smooth crabgrass control compared to mesotrione alone. The objectives of this research were to evaluate the influence of triclopyr on the efficacy, absorption, and translocation of mesotrione in multitiller smooth crabgrass. In field experiments, tank-mixing triclopyr at 560 or 1,120 g ae ha−1 with mesotrione at 140 g ai ha−1 applied sequentially or at 280 g ha−1 applied singly provided excellent control (> 90%) of multitiller smooth crabgrass in tall fescue. These treatments were more effective than mesotrione alone and fenoxaprop at 195 g ai ha−1 that averaged 66 and 81% control after 6 wk, respectively. Mesotrione alone at 280 g ha−1 bleached smooth crabgrass 53% at 2 wk after initial treatment (WAIT), and was 14% greater than the 140 g ha−1 treatment. Sequential treatments of the low mesotrione rate bleached smooth crabgrass 16 to 22% from 3 to 5 WAIT. Triclopyr tank mixtures reduced smooth crabgrass bleaching from mesotrione on all dates to < 5%. Tall fescue injury was not detected at any evaluation date. In laboratory experiments, smooth crabgrass reached peak foliar absorption of 14C-mesotrione at 24 and 168 h after treatment (HAT; 23% and 15%) when mesotrione was applied with triclopyr at 1,120 and 0 g ha−1, respectively. Triclopyr reduced translocation of radioactivity 12% at 72 and 168 HAT, compared to 14C-mesotrione alone. Enhanced foliar uptake of mesotrione from triclopyr tank mixtures might improve control of multitiller smooth crabgrass compared to mesotrione alone. Reduced foliar bleaching from triclopyr is associated with less translocation of mesotrione or derivatives in smooth crabgrass.
We have presented new observations of the ionized gas, molecular gas and cool dust in the Helix nebula (NGC 7293). The ionized gas is observed in the form of a Hα image, which is constructed using images from the Southern H-Alpha Sky Survey Atlas (SHASSA). The molecular emission was mapped using the H2v = 1 → 0 s(1) line at 2.122μm. The far-infrared (FIR) observations were obtained using ISOPHOT on the Infrared Space Observatory (ISO).
We are conducting a wide-angle Hα survey of the southern sky at CTIO using a robotic CCD camera. The survey consists of 283 fields covering the sky from δ = −90° to δ = +10°, with the same centers as those in the IRAS Sky Survey Atlas. As of July 1, 1998, it was about 45% complete. When all the images are obtained and fully processed, the survey will be made available to the scientific community on the web and on CD-ROM.