Using in vitro systems, numerous authors have cited the sensitivity of pollen tube growth to high temperature as a major cause of low yields for crops with valuable reproductive structures. We investigated the hypothesis that in vivo fertilization efficiency would be negatively affected by heat stress-induced changes in energy reserves and calcium-mediated oxidative status in the pistil. Gossypium hirsutum plants exposed to optimal (30/20 degrees C) or high day temperature (38/20 degrees C) conditions during flowering were analyzed for fertilization efficiency via UV microscopic observation of pollen tube-containing ovules and for soluble carbohydrates, adenosine triphosphate (ATP), calcium, antioxidant enzyme activity and NADPH oxidase (NOX; EC 1.6.3.1) activity in the pistil. Leaf measurements included gas exchange, chlorophyll content, quantum efficiency and ATP content of the subtending leaf on the day of anthesis. In the pistil fertilization efficiency, soluble carbohydrates, ATP content and NOX activity declined significantly, whereas water soluble calcium and glutathione reductase (EC 1.8.1.7) activity increased, and superoxide dismutase (EC 1.15.1.1) activity remained unchanged. In leaves, heat stress decreased photosynthesis, quantum efficiency and chlorophyll content, but increased stomatal conductance. We conclude that decreased source leaf activity either inhibits pollen development, tube growth through the style or guidance to the ovules as a result of an insufficient energy supply to the developing pistil. We further conclude that a calcium-augmented antioxidant response in heat-stressed pistils interferes with enzymatic superoxide production needed for normal pollen tube growth and fertilization of the ovule.

Jefferson counties in Arkansas to assess nonpoint source water pollution. During these 3 years, 59-62 lake and river/ stream sites were sampled eight times and screened for 17 pesticides commonly used in Arkansas. Pesticides were extracted by solid-phase extraction (SPE) disks. Extracts were analyzed by gas chromatography-electron capture detection (ECD) and high-performance liquid chromatography-UV detection (LCUV). Detections were confirmed by gas chromatography-mass spectroscopy (MS) or co-chromatography. The 256 detections during the survey represented 14 pesticides. Metolachlor (25% of total detections), atrazine (22%), norflurazon (16%), and cyanazine (14%) were the most commonly detected compounds. A total of 5% of the total detections was above health advisories. Spring and summer samples provided 73% of the total pesticide detections. Rivers and streams were responsible for 62% of the detections. The highest number of repeated detections of the same pesticide at a site was for cyanazine (six of eight sampling periods).

The stability of various pesticides in water at 4 °C was compared with their stability on C-18 SPE disks under three storage regimes. The disk storage regimes involved using the disk to extract the chemical from water, removing the disk and placing it in a plastic bag, and then storing it at either -20 or +4 °C for 1 day and then -20 °C for the remainder of the storage period. The storage periods included 0, 3, 30, 90, and 180 days. The percent recovery of each chemical was determined and used to compare storage treatments. Results indicate that the pesticides have equivalent or greater stability on solid-phase extraction disks compared to their storage in water at 4 °C. The data suggest that freezing the disk after pesticide loading is the most favorable storage option. Results show that field extraction/storage methodology is feasible, which could improve the reliability of future environmental water sampling procedures.

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Japanese honeysuckle presents a serious problem to the economically attractive natural regeneration of loblolly and shortleaf pine. This research investigated the potential allelopathic interference mechanisms of Japanese honeysuckle in relation to pine regeneration and growth, which may provide insight into overcoming this problem. The allelopathic potential of root exudates and leaf litter from Japanese honeysuckle was tested against loblolly and shortleaf pine seedlings. When Japanese honeysuckle and loblolly pine seedlings were grown using the same irrigation reservoir, there was no significant effect on the growth of either pine species. Exudates of Japanese honeysuckle grown as a pure culture in donor cups also produced no growth effects on pure-cultured pine seedlings grown in acceptor cups. In other assays, aqueous extracts of Japanese honeysuckle leaf tissue were toxic to duckweeds at concentrations well below levels where plasmolysis might cause effects. When Japanese honeysuckle leaf tissue was added to soil at a rate of 2 g tissue 100 g−1 soil, mean seedling height at 128 d after planting was reduced by as much as 40%. Moreover, pine seedlings grown in the presence of Japanese honeysuckle tissue exhibited significant chlorosis of the shoot and needles. Gas chromatography–mass spectroscopy analyses and high-performance liquid chromatography of Japanese honeysuckle leaf tissue aqueous extracts confirmed the presence of five compounds previously identified as possible allelochemicals: 4-hydroxycinnamic acid; 2-hydroxycinnamic acid; 3,4-dihydroxybenzoic acid; 3,4-dihydroxycinnamic acid; and chlorogenic acid. Results indicate that allelopathy plays at least a partial role in Japanese honeysuckle interference with loblolly and shortleaf pine.

Some accessions of rice (Oryza sativa L.) have been shown to inhibit the growth of barnyardgrass (Echinochloa crus‐galli (L.) Beauv.). Our objective was to determine if high‐performance liquid chromatography (HPLC) chromatograms from leaf extracts of different accessions of rice correlated with weed control activity. Chromatograms of extracts consisting of 10 mg of fresh leaf tissue per milliliter of methanol (CH3OH) were obtained from 40 accessions of rice. Cluster analysis was performed using 20 peaks from the chromatograms. Three clusters were found, with one cluster being distinctly separated from the other two. Although weed control data are not available for all the accessions, the isolated cluster contains all of the accessions that have been shown to inhibit growth of barnyardgrass and none that do not. This indicates that the assay could be used year‐round to screen accessions of rice for weed control potential to determine which accessions should be further tested in the field. This could be done in a relatively short time using a small amount of space in the greenhouse. Because the assay requires only 10 mg of tissue per milliliter of methanol, it may potentially be used to test individual plants within an accession for weed control potential in a nondestructive manner.

A year-long nurseryworker pesticide exposure study was designed to measure and evaluate the exposure occurring to workers who had the potential for simultaneous exposure to multiple pesticides. This four-State study was conducted in five nurseries (four USDA Forest Service and one State) involved in conifer seedling production. Primary comparisons were made among nursery workers in the Pacific northwest and south central United States. Worker exposure was assessed by using patches attached to clothing, handrinse samples and urine excreted from potentially exposed workers. In addition, dislodgeable residue in rinsate from a water wash of pesticide-treated seedlings was also evaluated. Four different groups of field workers, designated as applicators, weeders, scouts and packers, were included. The pesticide absorbed dose, assessed by urine analysis of pesticide metabolites and the deposition of pesticide on patches attached to the clothing of field workers, was monitored as they performed their duties under normal conditions (e.g., typical clothing, pesticide application). Monitoring was performed for the 14 different pesticides which were used in these nurseries. Seven pesticides were studied in more detail using biological monitoring. For these compounds, metabolites known to be excreted in the urine of exposed humans or other mammals were used to estimate the dose of pesticide absorbed by the exposed workers. The highest percentage of positive samples came from dislodgeable residue samples (8.3%) followed by patch samples (3.2%), handrinse (2.9%), and urine samples (1.3%). To summarize the conclusions from the urinary excretion data, 12 of the 73 nursery workers in the study received a low absorbed dose of pesticide. Biological monitoring revealed that three pesticides (benomyl, bifenox and carbaryl) were found in the urine of some of the workers. Of the 3,134 urine samples analyzed there were 42 positive; 11 urine samples were positive for benomyl, while bifenox was responsible for 13 positives and carbaryl accounted for the remaining 18. The 12-week continuous monitoring of urine showed that metabolites of these materials were rapidly excreted; thus, no build-up in the body is anticipated. Margins of Safety (MOS) calculations were made to provide an assessment of the significance of the exposure. Based on the low frequency of positive urine samples in the study, the low levels of metabolites when they were found, their apparent rapid excretion rate and the No Observed Effect Level (NOEL) data, furnished from other sources, nursery worker exposure to pesticides in these conifer nurseries is below health threatening levels.

Pesticides used in rice production have the potential to harm nontarget species. The objective of this study was to measure concentrations of selected rice pesticides in four rivers in eastern Arkansas from spring through mid-August for 2002 through 2008 to determine if changes over time might be leading to environmental water quality problems above a threshold of 2 µg L -1 (2 ppb). Most of the pesticide detections were in May, June, and early July. The probability of detecting a given compound in any sample ranged from 0.0042 on the St. Francis River to 0.0387 on the Cache River. After 2002, clomazone and quinclorac accounted for 55% to 96% of detections each year. Of the samples collected, 60% to 86% that contained a pesticide contained only one pesticide, and 12% to 34% of all samples collected contained two pesticides. Large concentrations were more common in samples collected upstream than those taken downstream. Clomazone and quinclorac were often detected on consecutive sampling dates, indicating the possibility that concentrations greater than 2 µg L -1 may be present over an extended period of time. Compared to ecotoxicity data, observed levels of these pesticides do not appear to be causing an environmental problem unless there is strong synergism between clomazone and quinclorac over a period of several weeks.