Phytotoxicity, absorption, translocation, and metabolism of root-applied norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3(2H)-pyridazinone] in tolerant narrowleaf and susceptible broadleaf guineagrass (Panicum maximum Jacq. # PANMA) biotypes were examined under greenhouse and laboratory conditions. Dose response studies conducted in the greenhouse showed greater injury to the shoots of broadleaf than narrowleaf biotypes. 14C-norflurazon absorbed was 0.3 and 0.5% and 1.6 and 2.4% of that applied, 3 and 7 days after application for narrowleaf and broadleaf biotypes, respectively. Of the total radioactivity absorbed after 3 and 7 days, 70 and 76% and 57 and 61% were translocated to the shoots of susceptible and tolerant biotypes, respectively. Gas chromatographic analyses revealed that broadleaf shoots had 3.08 μg/g dry wt of the parent compound while its tolerant counterpart had 0.40 μg/g dry wt, 7 days after application. The toxic parent compound was metabolized more rapidly to its non-phytotoxic desmethyl analog by narrowleaf biotypes, thereby preventing its accumulation in the shoots. Differences in absorption, translocation, and metabolism were responsible for the differential response of the two biotypes of guineagrass.

Root buds of leafy spurge (Euphorbia esula L. # EPHES) were found to be quiescent during most of the growing season due to correlative inhibition rather than innate dormancy. Excised root buds taken from plants that were fully flowering showed reduced elongation, indicating a period of innate dormancy. This innate dormancy could be eliminated by chilling plants for 8 days at 4 C. Root buds from plants showing late summer regrowth were no longer innately dormant. IAA (indole-3-acetic acid) and NAA (1-napthaleneacetic acid) completely inhibited the growth of excised leafy spurge root buds at concentrations of 10−3 and 10−5 M, respectively. A significant increase in root bud elongation was produced by 1 mM TIBA (2,3,5-triiodobenzoic acid) applied to stem and root tissue. These data provide further evidence for the involvement of IAA in correlative control of root bud growth in leafy spurge.

Various surgical cuts were used to induce germination of dormant barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] caryopses. Greater percentages of germination were obtained when the cuts were made closer to the embryo. However, removal of only the caryopsis coat covering the coleoptile or midembryo axis induced up to 10% germination compared to 70% germination for caryopses with the coat covering the radicle removed. Dormancy of barnyardgrass was not caused by the inability of the embryo to imbibe, imposed mechanical resistance of the caryopsis coat, or presence of an inhibitor. A wounding response, other than ethylene production, by the cut caryopses was possibly responsible for stimulating germination. Similar responses to cutting observed in afterripened caryopses were consistent with the suggested hypothesis.

Metabolism of 14C-pronamide [N-(1,1-dimethylpropynyl)-3,5-dichlorobenzamide, carbonyl- 14C] was studied in silt loam soil (located in Louvain-la-Neuve, Belgium) and in lettuce (Lactuca sativa L., ‘Appia′, Clause3) from a crop planted in soil that had been treated before planting. During the experiment, most of the 14C remained in the 0- to 6-cm soil layer. The percentage of 14C-pronamide degraded to 14CO2 during the experiment was less than 10%. The soil-extractable 14C was made up of pronamide and its first ketone metabolite [N-(1,1-dimethylacetonyl)-3,5-dichlorobenzamide]. About 30% of the pronamide present in the soil was bound to the soil. The bound residue, i.e., the 14C that could not be extracted by acetone, at lettuce harvest was about 80% of the 14C contained in the soil at that time; 3,5-dichlorobenzoic acid was the main component of the bound residue. The harvested lettuce also contained pronamide, the ketone, and 3,5-dichlorobenzoic acid. Similar kinetics of metabolism were observed with lettuces grown on loamy sand soil (located in St. Kathelijne-Waver, Belgium). However, pronamide was not bound to this type of soil.

The selectivity mechanisms of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} were investigated by examining absorption of 14C-sethoxydim into tissues of corn (Zea mays L. ‘Goldencrossbantam′) and pea (Pisum sativum L. ‘Alaska′). Greater absorption of 14C-sethoxydim was observed only into the proliferative 2-mm terminals of the excised roots of susceptible corn, and the same result was obtained with corn seedlings in hydroponic culture. Absorption was not affected by 1 × 10−4 M 2,4-dinitrophenol (DNP), which indicated that the absorption of 14C-sethoxydim is probably mediated by a passive transport system rather than an active transport system. The selective herbicidal action of sethoxydim appeared to depend largely on the differential rates of absorption into meristematic regions by the susceptible and tolerant plants.

The appearance of triazine resistance in a number of weed species has provided some opportunities for plant breeders to develop triazine-resistant crop varieties through classical breeding techniques. The sources of genes utilized by plant breeders for desirable characteristics are usually limited by the normal reproductive barriers that distinguish species. The occurrence of a triazine-resistant biotype of birdsrape mustard (Brassica campestris L. # BRSRA) has allowed for the development of commercially useful triazine-resistant varieties of canola (low erucic acid, low glucosinolate oilseed rape, B. napus L.). The cytoplasm of triazine-resistant birdsrape mustard was transferred interspecifically to oilseed rape, by a technique commonly known as back-crossing, in conjunction with selection for chromosome number. ‘OAC Triton′, the first triazine-resistant canola variety, appears to be finding commercial acceptance in Canada, in spite of some limitations in agronomic performance. Although it should be possible to transfer this triazine-resistant cytoplasm to other economic Brassica species including the cole crops and mustards, conventional plant breeding techniques cannot separate the gene conferring triazine resistance from other genes in the resistant weed biotype's cytoplasm. This problem may limit the utility of triazine-resistant cytoplasms from weed biotypes in classical crop breeding.

Greenhouse experiments were conducted to elucidate the effects of water stress on photosynthetic parameters of soybean [Glycine max (L.) Merr. ‘Hutton′] and velvetleaf (Abutilon theophrasti Medik. # ABUTH). Stomatal conductance of both species responded curvilinearly to reductions in leaf water potential. At leaf water potentials less negative than −2.5 MPa, stomatal conductance, net photosynthetic rate, and transpiration rate were greater in velvetleaf than in soybean. Soybean photosynthetic rate was linearly related to stomatal conductance. Velvetleaf photosynthetic rate increased linearly with stomatal conductances up to 1.5 cm s–1; however, no increase in photosynthetic rate was observed at stomatal conductances greater than 1.5 cm s–1, indicating nonstomatal limitations to photosynthesis. As water stress intensified, stomatal conductance, photosynthetic rate, and transpiration of velvetleaf declined more rapidly than in soybean.

Seeds of green foxtail [Setaria viridis (L.) P. Beauv. # SETVI] and giant foxtail (S. faberi Herrm. # SETFA) were collected from mature plants in the field and recovered from three soil depths under two types of tillage. Fungi colonizing the caryopses were isolated to determine the effect of tillage and soil depth on fungal colonization and the field flora. Alternaria alternata (Fr.) Keissler and Epicoccum purpurascens Ehrenb. ex Schlecht. were the two fungi most frequently isolated from the hand-harvested seeds. Percentages of fungal colonization were directly related to size of the caryopses. The most frequently isolated fungus species recovered from seeds from soil were A. alternata, Cladosporium cladosporioides (Fresen.) de Vries, E. purpurascens, and two unidentified fungi with sterile mycelium. One sterile fungus had white rough mycelium, and the other had dark mycelium. These two sterile fungi had a detrimental effect on foxtail seed germination in the laboratory. Caryopsis colonization seems to be related to the placement of the crop residues in the soil. In reduced-tillage plots, more caryopses were colonized in the top soil layer (0 to 7.5 cm) than in the 7.5- to 15-cm layer. In plowed soils, greater colonization occurred at the lower depth.

The basis for chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] caronyl] benzenesulfonamide} antagonism of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} was investigated in Italian ryegrass [Lolium multiflorum (Lam.) # LOLMU] and wheat (Triticum aestivum L. ‘McNair 1813′). Chlorsulfuron did not affect the chemical stability or volatility of diclofop in spray mixtures over the time and concentration ranges evaluated. Addition of chlorsulfuron (0.11 μg/μl) to a diclofop (2.0 μg/μl) foliar-applied spotting solution did not affect the absorption, translocation, or metabolism of diclofop in 17-day-old Italian ryegrass or wheat. Italian ryegrass and wheat responded differentially to diclofop alone. At 72 h after treatment, 69 and 40% of labeled diclofop penetrated into Italian ryegrass and wheat leaves, respectively. Although little movement of labeled diclofop occurred in either species, more translocated from the treated zone of Italian ryegrass. At 72 h after treatment, the percentages of 14C recovered as parent methyl ester, diclofop (free acid), and conjugates in treated leaf extracts were 9, 62, and 25%, respectively, for Italian ryegrass, and 50, 20, and 29%, respectively, for wheat. Differential penetration and metabolism of diclofop are the probable bases for selectivity between wheat and Italian ryegrass. The antagonism of diclofop caused by chlorsulfuron does not appear to be due to an alteration of the molecular fate of diclofop in Italian ryegrass.

A quantitative assay using 14C-chloramben (3-amino-2,5-dichlorobenzoic acid) revealed that velvetleaf (Abutilon theophrasti Medic. # ABUTH) leaves absorbed a greater amount of chloramben formulated as an acid than as a sodium salt. A surfactant increased 14C-chloramben absorption 5 days, but not 1 day, after application. Translocation of 14C-label out of treated leaves was greater in velvetleaf than in soybean [Glycine max (L.) Merr.]. Differences in the amount of 14C-label as unmetabolized chloramben in ethyl acetate extracts of treated leaves were not detected between velvetleaf and soybean. The amount of unmetabolized chloramben was greater in the shoot above the treated leaf in velvetleaf (58% of total label recovered) than in soybean (35% of recovered label). The amount of recovered 14C-label in unextractable form was greater in treated leaves of soybean compared to velvetleaf.

The potential of mourning doves (Zenaida macroura L.) as dispersers of leafy spurge (Euphorbia esula L. # EPHES) seeds was investigated by examing digestive tract contents and feces. Very few intact seeds passed through the digestive systems of wild or captive adult mourning doves. An average of less than one intact leafy spurge seed/g was recovered from fecal material found in dove nests. These results suggest that adult mourning doves are primarily consumers of leafy spurge seeds and rarely act as dispersal agents. It appears that dispersal is only possible when seeds passing through the digestive tracts of nestlings are deposited in the nest and the nest later falls.

The soil bacterium Alcaligenes eutrophus is able to degrade phenoxy herbicides such as 2,4-D [(2,4-dichlorophenoxy)acetic acid]. It has been shown that several degradative genes are located on a large plasmid harbored by this organism. We have demonstrated by HPLC and gas chromatography that 2,4-dichlorophenol is a major metabolite resulting from 2,4-D degradation by A. eutrophus. A portion of the large plasmid carrying the 2,4-D catabolic genes has been cloned and mapped by restriction endonuclease digestion. Overlapping subclones have been produced and were used in conjugation experiments in order to identify the first gene involved in 2,4-D detoxification. Once sequenced, this gene will be transferred to dicotyledonous plant cells using available vector systems.

In controlled-environment chambers, the scentless plant bug Niesthrea louisianica Sailer damaged reproductive structures of velvetleaf (Abutilon theophrasti Medik. # ABUTH) and reduced viable seed production by 98 to 99%, in comparison with insect-free control plants. The insect completed its life cycle on velvetleaf in two temperature regimes simulating warm growing-season conditions in Mississippi (29/23 C day/night) and Minnesota (24/18 C). Feeding by N. louisianica delayed flowering, capsule development, and capsule and seed maturation in biotypes of velvetleaf from Mississippi and Minnesota, in both temperature regimes. Numbers and weights of capsules and seed were lower in the infested plants. Augmentation of natural populations of N. louisianica to increase population density early in the growing season might be effective in reducing velvetleaf seed production.

Seed of 41 accessions of Crotalaria representing 35 species were analyzed for the concentration of total pyrrolizidine alkaloids (PAs) and for oral toxicity to 1-week-old chicks. All accessions were assayed for the presence of monocrotaline and spectabiline by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). High concentrations of PA were found in the seed of Crotalaria spectabilis Roth # CVTSP (3.85%), C. retusa L. (2.69%), C. alata Leveille (1.60%), C. quinquefolia L. (1.19%), and C. argyrolobioides Bak. (1.01%). The seed of Crotalaria argyrolobioides produced toxic signs but no deaths when fed at 10 mg/g of body weight, whereas the seed of the other four species were 100% lethal when fed to chicks in one dose at 2 to 6 mg/g of body weight. Seed of other species contained less than 0.6% PA and were nontoxic to chicks fed one dose at 10 mg/g of body weight. Monocrotaline was identified in 17 accessions and spectabiline in 7. No species contained both monocrotaline and spectabiline.

14C-chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} and its metabolites were extracted from flax (Linum sativum L.), field penny cress (stinkweed) (Thlaspi arvense L. # THLAR), and wheat (Triticum aestivum L.) with an average efficiency of 94% using an aqueous extraction procedure. Chlorsulfuron and its metabolites were separated on a reverse-phase preparative chromatography column by eluting with a step gradient of aqueous 0.1% (v/v) formic acid and methanol. Major peaks were eluted at 35 and 45% methanol, and minor peaks at 10, 25, and 100% methanol. The 45% methanol peak represented unmetabolized chlorsulfuron or its hydroxylated derivative and was the only fraction that exhibited biological activity. In wheat and flax, 75 and 62%, respectively, of the extracted activity were eluted by 35% methanol and, in the case of wheat, this fraction was shown to be a glycosylated derivative of chlorsulfuron. Although 14C-chlorsulfuron was metabolized to a lesser extent in field pennycress, our data indicate that over 50% of the absorbed 14C-activity was recovered in forms other than 14C-chlorsulfuron 5 days after treatment. The separation procedure can be used readily to assess the amount of chlorsulfuron detoxification that occurs in plants.

The target site of glyphosate [N-(phosphonomethyl)glycine] inhibition in plants and bacteria is 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase. Our strategy for developing glyphosate-resistant crops has been to genetically engineer plants with a gene that codes for EPSP synthase with low sensitivity in glyphosate. We cloned such a gene from the aroA locus of a glyphosate-resistant mutagenized strain of Salmonella typhimurium. The enzyme encoded by this gene has a single amino acid change resulting in lower affinity for glyphosate and higher affinity for substrates than either plant or wild-type bacterial counterpart. A chimaeric gene containing the mutant aroA gene behind the octopine synthase promoter was constructed and integrated into Agrobacterium T-DNA vectors. Analysis of gall tissue from Brassica campestris L. (turnip rape) infected with A. tumefaciens K12 containing this chimaera showed mRNA and protein expressed from the bacterial gene; 50% of the total EPSP synthase activity present had kinetic properties of the mutant bacterial enzyme. Tobacco (Nicotiana tabacum L. ‘Xanthi′) plants have been regenerated from cocultivation with A. rhizogenes containing the same construct; analysis indicates expression of the gene and enhanced tolerance to glyphosate.

A comparison of the structure of the α-methylbenzyl analogue (MBAT) of atrazine with the Photosystem II herbicides atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea] suggested that N-alkylbenzyltriazines may be a structural bridge between the triazines and the phenylureas. In the phenylureas, the addition of chlorines at the meta and/or para positions produces a marked increase in activity. Chloro-substituted derivatives of MBAT were synthesized to determine whether this structure-activity relationship also applies to the alkylaryltriazines. Addition of a chlorine to MBAT at the 4-position (CMBAT) caused a substantial increase in intrinsic activity, and a second chlorine at the 3-position (DCMBAT) caused a further increase. In direct comparisons, DCMBAT was more active in vitro than terbuthylazine [6-chloro-N-ethyl-N′-(1,1-dimethylethyl)-1,3,5-triazine-2,4-diamine], the most active chlorotriazine, and was also more active than diruon. The effects of DCMBAT were also measured on triazine-resistant pigweed (Amaranthus hybridus L. # AMACH) both in vivo and in vitro. The activity of this compound in triazine-resistant chloroplasts was intermediate between that of atrazine and diruon both in inhibition of photosynthetic electron transport and in competition for diuron binding sites, with half-maximal values falling in the micromolar range. Whole plant phytotoxicity of DCMBAT on triazine-resistant pigweed was also intermediate between that of diuron and atrazine. Since DCMBAT is a triazine with biological properties similar to that of a urea, we conclude that in a functional as well as structural sense, DCMBAT is a herbicide that is a hybrid between a triazine and a urea.

Net (apparent) photosynthesis rate (Pn) of jointed goatgrass (Aegilops cylindrica Host # AEGCY) leaves in the greenhouse became light saturated at a photosynthetic photon flux density (PPFD) of about 1000 μE·m–1-2·s–1 with a maximum Pn of 27 mg CO2 ·dm–2 ·h–1. Diffusive resistance to water vapor (rl) of adaxial leaf surfaces was 43% that of abaxial surfaces, in part, because stomatal density was 50% greater on adaxial leaf surfaces than on abaxial surfaces. Dark respiration rate (Rd) was 1.6 mg CO2 ·dm−2·h−1. Light compensation point (CPl) was 21 μE·m−2·s−1 and CO2 compensation point (CPc) was 32 ppmv. In the field, where light intensity and temperature were greater than in the greenhouse, leaves became light saturated for Pn at a higher intensity, and Rd and CPl were three times greater than in the greenhouse. Pn and Rd of spikes at anthesis were at least 30% less and 200% greater, respectively, than the values for leaves.

Reductions in yields of processing tomatoes (Lycopersicon esculentum Mill. ‘H2653’ and ‘Earlirouge′) caused by interference from eastern black nightshade (Solanum ptycanthum Dun. # SOLPT) and hairy nighthsade (S. sarrachoides Sendt. # SOLSA) were estimated for transplanted and seeded tomatoes at two locations in southern Ontario. Tomato yield losses were significantly greater in seeded than in transplanted tomatoes. Stomatal conductance and transpiration rates of seeded tomatoes decreased more rapidly with increased nightshade density than did those of transplanted tomatoes. Percent yield losses also differed between sites. Seeded tomatoes grown at high density in twin rows (33 300 and 45 000 plants/ha) had higher yields and lower percent yield losses than did tomatoes grown at low density in single rows (12 500 to 22 500 plants/ha). Nightshade dry weight and seed production decreased per plant but increased per unit area with increasing nightshade density. Nightshade dry weights and seed production did not vary with site or method of tomato establishment. A hyperbolic model provided an excellent fit to data on both tomato yield losses and nightshade seed production as a function of nightshade density.

The influence of two weed management systems was determined on weed seed and seedling populations and on yields of cantaloupe (Cucumis melo L. var. reticulatus Naudin ‘Perlita′), bell pepper (Capsicum annuum L. var. grossum ‘Grande Rio 66′), cotton (Gossypium hirsutum L. ‘CP 3374′), onion (Allium cepa L. ‘1015Y′), and cabbage (Brassica oleracea, var. capitata L. 'Sanibel′) sequentially grown in two 3-yr cycles. Palmer amaranth (Amaranthus palmeri S. Wats. # AMAPA) did not exist initially, but hurricane-introduced seed populations increased to 1.1 billion/ha as seed populations of common purslane (Portulaca oleracea L. # POROL) decreased from 786 million/ha to 124 million/ha in the 6-yr period, without weeding or herbicide. Use of herbicides and handweeding reduced Palmer amaranth seed populations 98%, but 18 million/ha still remained after 6 yr. The use of herbicides and Palmer amaranth interference decreased the seed populations of common purslane by 84%, but handweeding was inefficient. Yields of all but the first crop of cantalouple were almost totally eliminated by season-long interference of Palmer amaranth. Savings with the utilization of herbicides rather than handweeding ranged from $62/ha for cotton to $4703/ha for bell pepper.