Black scurf and stem canker of potato (Corticium Solani Bourd. & Galz.)

Black scurf and stem canker of the potato was investigated in field trials on infected soil at Warburton, Cheshire, to study the effect of planting clean and contaminated seed, and the relation between the dates of planting and lifting and the contamination of the crop tubers.
Black scurf was prevalent on crops grown from clean seed but was more severe on crops raised from contaminated seed. Under conditions favourable for the disease the yields from clean and contaminated seed were satisfactory and were not significantly different. Young shoots of plants from contaminated seed were severely attacked and tuber formation was checked; these results were not obtained on clean seed plots.
More black scurf occurred on late-dug crops; on early-dug plots the disease, although almost absent in 1941, was prevalent in 1942. Late planting failed to reduce appreciably the amount of black scurf.
Variety trials included Arran Banner, Kerr's Pink (two vigorous varieties), King Edward and Majestic (two less vigorous varieties). All were heavily infected and each recovered well from an attack on the young shoots.
Inoculation of the seed at planting time did not affect the results; in all trials, misses and wilted shoots caused by Corticium were rare and there was no relation between the yield and the amount of black scurf on the crop tubers.
The results indicate that the disease causes little, if any, loss under farm conditions.     

Frequency and distance of pollen dispersal from transgenic oilseed rape (Brassica napus)

The objective of this study was to evaluate pollen dispersal inBrassica napus (oilseed rape). The selectable marker, used to follow pollen movement, was a dominant transgene (bar) conferring resistance to the herbicide glufosinate-ammonium. Transgenic and non-transgenic plants of the cultivar Westar were planted in a 1.1 ha field trial, with the transgenic plants in a 9 m diameter circle at the centre, surrounded by non-transgenic plants to a distance of at least 47 m in all directions. A 1 m circle of non-transgenic plants was sown in the centre of the transgenic area to allow estimation of the level of pollen dispersal when plants were in close contact. Honeybee hives were placed at the trial site to optimize the opportunity for cross-pollination. During the flowering period, regular observations were made of the number of plants flowering and the number and type of insects present in 60 1 m² areas. These areas were located uniformly around the plot at distances of 1, 3, 6, 12, 24, 36 and 47 m from the edge of the 9 m circle of transgenic plants. Seed samples were harvested from each of the 7 distances so that approximately 20% of the circumference of the plot was sampled at each distance. The centre non-transgenic circle was also sampled. Plants were grown from the seed samples and sprayed with glufosinate to estimate the frequency of pollen dispersal at each distance. In order to screen enough samples to detect low frequency cross-pollination events, seed samples were tested in the greenhouse and on a larger scale in the field. Results were confirmed by testing progeny for glufosinate resistance and by Southern blot analysis. The estimated percentage of pollen dispersal in the non-transgenic centre circle was 4.8%. The frequency was estimated to be 1.5% at a distance of 1 m and 0.4% at 3 m. The frequency decreased sharply to 0.02% at 12 m and was only 0.00033% at 47 m. No obvious directional effects were detected that could be ascribed to wind or insect activity.     

Gene flow from transgenic to nontransgenic soybean plants in the Cerrado region of Brazil

Evaluation of transgenic crops under field conditions is a fundamental step for the production of genetically engineered varieties. In order to determine if there is pollen dispersal from transgenic to nontransgenic soybean plants, a field release experiment was conducted in the Cerrado region of Brazil. Nontransgenic plants were cultivated in plots surrounding Roundup Ready transgenic plants carrying the cp4 epsps gene, which confers herbicide tolerance against glyphosate herbicide, and pollen dispersal was evaluated by checking for the dominant gene. The percentage of cross-pollination was calculated as a fraction of herbicide-tolerant and -nontolerant plants. The greatest amount of transgenic pollen dispersion was observed in the first row, located at one meter from the central (transgenic) plot, with a 0.52% average frequency. The frequency of pollen dispersion decreased to 0.12% in row 2, reaching 0% when the plants were up to 10 m distance from the central plot. Under these conditions pollen flow was higher for a short distance. This fact suggests that the management necessary to avoid cross-pollination from transgenic to nontransgenic plants in the seed production fields should be similar to the procedures currently utilized to produce commercial seeds.     

Surveying of pollen-mediated crop-to-crop gene flow from a wheat field trial as a biosafety measure

Outcrosses from genetically modified (GM) to conventional crops by pollen-mediated gene flow (PMGF) are a concern when growing GM crops close to non-GM fields. This also applies to the experimental releases of GM plants in field trials. Therefore, biosafety measures such as isolation distances and surveying of PMGF are required by the regulatory authorities in Switzerland. For two and three years, respectively, we monitored crop-to-crop PMGF from GM wheat field trials in two locations in Switzerland. The pollen donors were two GM spring wheat lines with enhanced fungal resistance and a herbicide tolerance as a selection marker. Seeds from the experimental plots were sampled to test the detection method for outcrosses. Two outcrosses were found adjacent to a transgenic plot within the experimental area. For the survey of PMGF, pollen receptor plots of the conventional wheat variety Frisal used for transformation were planted in the border crop and around the experimental field up to a distance of 200 m. Although the environmental conditions were favorable and the donor and receptor plots flowered at the same time, only three outcrosses were found in approximately 185,000 tested seedlings from seeds collected outside the experimental area. All three hybrids were found in the border crop surrounding the experimental area, but none outside the field. We conclude that a pollen barrier (border crop) and an additional isolation distance of 5 m is a sufficient measure to reduce PMGF from a GM wheat field trial to cleistogamous varieties in commercial fields below a level that can be detected.     

Growth and yield of winter wheat (Triticum aestivum L.) and corn (Zea mays L.) near a high voltage transmission line

The objective of this study was to determine the effects of an electromagnetic field from a high voltage transmission line on the yield of agricultural crops cultivated underneath and near the transmission line. For 5 years, experiments with winter wheat and corn were carried out near the 380 kV transmission line Dürnrohr (Austria)-Slavetice (Czech Republic). Different field strengths were tested by planting the crops at different distances from the transmission line. The plants were grown in experimental plots (1.77 m2), aligned to equal electric field strengths, and were cultivated according to standard agricultural practice. The soil for all plots was homogenized layer-specifically to a depth of 0.5 m to guarantee uniform soil conditions in the plant root environment. The soil was sampled annually for determinations of carbon content and the behavior of microbial biomass. During development of the vegetation, samples were collected at regular intervals for growth rate analyses. At physiological maturity, the plots (n = 8) were harvested for grain and straw yield determinations. The average electric and magnetic field strengths at four distances from the transmission line (nominal distances: 40, 14, 8, and 2 m) were between 0.2 and 4.0 kV/m and between 0.4 and 4.5 micro T, respectively. No effect of the field exposures on soil microbial biomass could be detected. The wheat grain yields were 7% higher (average of 5 years) in the plots with the lowest field exposure than in the plots nearer to the transmission line (P <.10). The responses of the plants were more pronounced in years with drought episodes during grain filling than in humid years. No significant yield differences were found for corn yields. The extent of the yield variations attributed to the distance from the transmission line was small compared to the observed annual variations in climatic or soil specific site characteristics.     

Monitoring the Spread of Recombinant DNA from Field Plots with Transgenic Sugar Beet Plants by PCR and Natural Transformation of Pseudomonas Stutzeri

Previous studies had shown that recombinant DNA can be detected for several months in soil after the deposition of litter from transgenic (tg) plants. Here we show by PCR monitoring of field releases of tg sugar beet plants that during the growth of the plants the soil close to the plants and also plant material contains recombinant DNA, in the form of extracellular molecules. Surprisingly, the monitoring also revealed the presence of tg DNA in many field plots (30–70%) in which tg plants were never grown. These studies and the further monitoring during other tg sugar beet release experiments by PCR and a novel bioassay (measuring the transforming potential of recombinant DNA for Pseudomonas stutzeri) indicated that recombinant DNA was only detectable in the surface soil of field plots and their vicinity where flowering of the tg beet plants was allowed. Recombinant DNA was found in soil at a distance of 50 m from pollen-producing plants surrounded by a strip with hemp plants as a containment regime. It is concluded that recombinant DNA is deposited in soil during the growth of tg sugar beets and that a major mechanism of recombinant DNA spread in the environment is the dispersal of pollen which allows recombinant DNA to persist in the field plot for at least a year.     

Factors of pine-stand transformation in the city of Yekaterinburg

The relationships between the health of Pinus sylvestris trees and stands and the levels of anthropogenic stress and fragmentation of habitats have been studied based on the example of pine stands of natural origin in Yekaterinburg and its vicinity (48 sampling plots located at different distances from the center of the city). The distances from the city center and from the boundary of a built-up area to a sampling plot and the population density around this plot are taken to characterize the level of anthropogenic stress. The area and perimeter of a forest site; the distance from the boundary of a sampling plot to the forest edges; and the shape of forest edges are used to characterize the level of fragmentation of habitats. We have found that the average morphological metrics of trees have slight changes, while the traits of tree health are significantly altered under urban environment. The overall performance of stands decreases by 22–35% in the urbanization gradient. The health of stands is most substantially influenced by the forest-site area. The population density around sampling plots and the distance of these plots from the megalopolis center have a lower effect on the health of trees and stands. Fragmentation of forests in the city leads to a decrease in the size of forest sites, which causes a decrease in wood stocks and the diameter and height of trees and the deterioration of their health. The lowest area of the forest to make it sustain an urban environment is about 30 ha. The untransformed core of forest is located no less than 70 m from the forest edge.     

Effect of Proximity to a Cattle Feedlot on Escherichia coli O157:H7 Contamination of Leafy Greens and Evaluation of the Potential for Airborne Transmission

The impact of proximity to a beef cattle feedlot on Escherichia coli O157:H7 contamination of leafy greens was examined. In each of 2 years, leafy greens were planted in nine plots located 60, 120, and 180 m from a cattle feedlot (3 plots at each distance). Leafy greens (270) and feedlot manure samples (100) were collected six different times from June to September in each year. Both E. coli O157:H7 and total E. coli bacteria were recovered from leafy greens at all plot distances. E. coli O157:H7 was recovered from 3.5% of leafy green samples per plot at 60 m, which was higher (P < 0.05) than the 1.8% of positive samples per plot at 180 m, indicating a decrease in contamination as distance from the feedlot was increased. Although E. coli O157:H7 was not recovered from air samples at any distance, total E. coli was recovered from air samples at the feedlot edge and all plot distances, indicating that airborne transport of the pathogen can occur. Results suggest that risk for airborne transport of E. coli O157:H7 from cattle production is increased when cattle pen surfaces are very dry and when this situation is combined with cattle management or cattle behaviors that generate airborne dust. Current leafy green field distance guidelines of 120 m (400 feet) may not be adequate to limit the transmission of E. coli O157:H7 to produce crops planted near concentrated animal feeding operations. Additional research is needed to determine safe set-back distances between cattle feedlots and crop production that will reduce fresh produce contamination.     

Black scurf and stem canker of potato (Corticium Solani Bourd. & Galz.): Further field studies on the use of clean and contaminated seed potatoes and on the contamination of crop tubers

Black scurf and stem canker of the potato were investigated in field trials in contaminated soil at Warburton, Cheshire, to determine the effect of planting clean and contaminated seed (vars. Arran Banner and Majestic) on crop yield and on the contamination of the crop tubers.
Black-scurf contamination was prevalent on crops grown from clean seed and was not significantly different from that occurring on plots planted with contaminated seed. It was severe on early-dug tubers, but was more severe on late-dug tubers. Produce grown with and without stable manure was heavily contaminated.
Contaminated seed caused a check to tuber formation and an appreciable increase in stem canker and in the number of primary shoots killed. Nevertheless, the yields from the manured, contaminated seed plots were satisfactory and were not lower than those from the clean-seed plots. There was no relation between the yield and the amount of black scurf on the produce.
The results of a trial made in a field which had been in grass for at least 43 years, suggested that the soil contained little, if any, Corticium Solani. Heavy contamination occurred on tubers grown under relatively dry soil conditions.
In all the trials misses and wilted shoots caused by Corticium were rare and there was no premature yellowing or death of the haulms on the clean or contaminated seed plots.
The evidence obtained in the four seasons from 1941 to 1944 indicates that in this country satisfactory yields of early maincrop and maincrop varieties may be obtained despite the prevalence of C. Solani in the soil and on the seed, provided the soil and cultural conditions are reasonably good.     

The effects of a bumble bee nectar robber on plant reproductive success and pollinator behavior

Interactions between a plant species (Corydalis caseana), a bumble bee nectar robber (Bombus occidentalis), and a bumble bee pollinator (B. appositus) were studied. There were no significant differences between naturally robbed and unrobbed flowers in fruit set or mean seed set per fruit. Plots of C. caseana plants were subjected to treatments of robbing and no robbing using commercially available colonies of B. occidentalis. Robbers did not pollinate the flowers. Pollinator behavior was observed to determine (1) the number of bees attracted to each plot, (2) the number of inflorescences visited in a plot, (3) the number of flowers visited on each inflorescence, and (4) the distance flown between inflorescences. There were no significant differences in the number of inflorescences visited per bee or the number of flowers visited per inflorescence per bee when robbed and unrobbed treatments were compared. Of the parameters measured, only distance flown between inflorescences differed in the robbed and the unrobbed treatments. Bees flew significantly further between inflorescences in the robbed plots than in the unrobbed plots. The results indicate that the nectar robbers have no negative effect on fruit set or seed set in C. caseana and that they may cause increased pollen flow distances by changing the behavior of the pollinator.     

EFFECTS OF DISTANCE BETWEEN POLLEN DONOR AND POLLEN RECIPIENT ON FITNESS COMPONENTS IN ESPELETIA SCHULTZII

The effect of flowering time and of distance between pollen donor and pollen recipient on the proportion of filled achenes, aborted seeds, and seedling survivorship was studied in populations of Espeletia schultzii in the Venezuelan Andes. Hand-pollinations were performed in two different years and at different times during the flowering season. Pollinations within-population included crosses between plants within a few meters to a maximum of 500 m apart and between-population pollinations included crosses between plants more than 10 km and up to 78 km away. Late in the flowering season, plants suffered a reduction in the proportion of filled achenes and an increase in aborted seeds. The proportion of filled achenes and aborted seeds did not vary significantly between the distances between pollen and ovules in crosses done early in the flowering season. However, the proportion of filled achenes in crosses between individuals within 30 m distance were very variable, either very successful or not successful. Beyond 30 m, for some of the populations, the frequency of unsuccessful crosses was almost 0. This pattern was observed at three elevation sites in two consecutive years. When crosses were done late in the flowering season, the proportion of filled achenes was lower in crosses between close individuals and between very distant ones. Seedling survivorship varied significantly between the crossing distances at the higher elevation only. The results show that a clear effect of the incompatibility alleles on the crossing success of the plants is present in the different populations examined, while they suggest that the effect of inbreeding or outcrossing depression is less clear but might still be present only under certain conditions. Late in the season, when plants might have fewer resources available for reproduction and at the high and intermediate site where cold and dry environmental conditions are less favorable for the plants, the discrimination among distances was stronger.     

Environmental and biotic drivers of soil microbial β‐diversity across spatial and phylogenetic scales

Soil microbial communities play a key role in ecosystem functioning but still little is known about the processes that determine their turnover (β‐diversity) along ecological gradients. Here, we characterize soil microbial β‐diversity at two spatial scales and at multiple phylogenetic grains to ask how archaeal, bacterial and fungal communities are shaped by abiotic processes and biotic interactions with plants. We characterized microbial and plant communities using DNA metabarcoding of soil samples distributed across and within eighteen plots along an elevation gradient in the French Alps. The recovered taxa were placed onto phylogenies to estimate microbial and plant β‐diversity at different phylogenetic grains (i.e. resolution). We then modeled microbial β‐diversities with respect to plant β‐diversities and environmental dissimilarities across plots (landscape scale) and with respect to plant β‐diversities and spatial distances within plots (plot scale). At the landscape scale, fungal and archaeal β‐diversities were mostly related to plant β‐diversity, while bacterial β‐diversities were mostly related to environmental dissimilarities. At the plot scale, we detected a modest covariation of bacterial and fungal β‐diversities with plant β‐diversity; as well as a distance–decay relationship that suggested the influence of ecological drift on microbial communities. In addition, the covariation between fungal and plant β‐diversity at the plot scale was highest at fine or intermediate phylogenetic grains hinting that biotic interactions between those clades depends on early‐evolved traits. Altogether, we show how multiple ecological processes determine soil microbial community assembly at different spatial scales and how the strength of these processes change among microbial clades. In addition, we emphasized the imprint of microbial and plant evolutionary history on today's microbial community structure.     

Pollen-mediated transgene flow in the wind-pollinated grass species tall fescue (Festuca arundinacea Schreb.)

Information regarding gene flow in wind-pollinated, outcrossing forage grasses is essential for any future releases of value-added transgenic cultivars. Experiments on pollen dispersal was carried out by growing transgenic tall fescue (Festuca arundinacea) in a central plot, surrounded by exclosures containing recipient plants up to a distance of 200 m from the central source plants in eight directions. The central transgenic tall fescue plants carried a chimeric hygromycin phosphotransferase gene (hph) and a chimeric -glucuronidase gene (gusA). Seeds were collected from the recipient plants and germinated seedlings were used for high throughput DNA isolation and polymerase chain reaction (PCR) analysis. More than 21,000 seedlings were PCR analyzed for the experiments conducted in three years. Transgenes were detected in recipient plants at up to 150 m from the central transgenic plot. The highest transgene frequencies, 5% at 50 m, 4.12% at 100 m and 0.96% at 150 m, were observed north of the central plot, the prevailing wind direction. Lower transgene frequencies were detected in other directions, particularly at 100 m and 150 m distances. No transgene was detected at 200 m distance in any direction. Transgene flow was less effective or ineffective when recipient plants were further away from the central donor plants. Southern blot hybridization analysis confirmed the transgenic nature of the PCR positive plants. A supplementary experiment demonstrated that transgene flow can be controlled by placing transgenic plantings downwind and long distances from non-transgenic seed increases, thus allowing tall fescue breeding and transgene development programs to be conducted concurrently at the same research station.     

Effect of chlorocholine chloride and gibberellic acid on the anthocyanin synthesis in radish seedlings

Anthocyanin synthesis in radish ( Raphanus sativus L. cv. Scarlet Globe) seedlings after treatment with chlorocholine chloride (CCC) and gibberellic acid (GA) has been investigated. CCC promotes and GA₃ inhibits the synthesis. When both substances are given together, CCC reverses the inhibition caused by GA₃. Simultaneous external feeding of anthocyanin precursors (sucrose and phenylalanine) reverses the GA₃ inhibition. A higher amount of total free amino acids, in particular phenylalanine, was present in CCC-treated seedlings compared to controls grown on distilled water. The amount of phenylalanine was lower in seedlings treated with both CCC and GA₃ as compared to seedlings treated with CCC alone, and total free sugars (reducing plus non-reducing) was lower in CCC treated seedlings than in controls grown on distilled water. We conclude that CCC and GA3 control the anthocyanin synthesis at the level of precursors.     

洪水干扰对青冈种群更新的影响

本文在安徽黄山选择位于溪谷、受洪水干扰程度不同的3个样地,调查青冈种群的更新特征,结论如下：①从幼苗数量来看,受洪水影响最轻的样地3最多,密度为0.5825株m-2,洪水影响最严重的样地1数量最少,密度仅为0．1150株m-2;从幼苗性质来看,样地1萌生苗比率最高．3个样地中,随着高度级别增加,萌生苗的比例也增加。②萌生苗高度的分布接近于对称的低峰分布,实生苗的偏斜度均为正值。所有的Gini系数都较大,平均为0．5260,说明大小不等性较大。③3个样地中萌生苗均为集聚分布,样地2、3中实生苗为随机分布,而样地1由于洪水干扰较严重,实生苗多集中于地势较高的一端,呈集聚分布。以上结果表明,青冈种群的更新受洪水影响较大,溪谷种群形成了以无性繁殖为主的更新对策。     

Storage Organ Development in Radish (Raphanus sativus L.). 1. A Comparision of Development in Seedlings and Rooted Cuttings of Two Contrasting Varieties

Development was compared in two contrasting varieties of radishgrown in nutrient solution. Differences in shape of the long,tapering radish of Long White Icicle and the smaller, roundCherry Belle were associated with differences in the growthof the upper part of the tap root. Thickening was the resultof , cambial activity and transverse scctions through the upperroot showed differences in both cell number and a l l size.Long White Icicle contained more cells in the secondary xylemand phloem/secondary cortex than Cherry Belle, and the non-lignifiedxylem parenchyma cells were also larger in Icicle. The upperpart of the tap root also elongated in Icicle but not in CherryBelle, and this was entirely due to an increase in cell numberin the longitudinal plane. Removing the distal part of the root system had little effecton storage organ size unless most of the root system was removed.Adventitious roots on seedling and shoot-tip cuttings of bothvarieties were capable of thickening and the single root developingon shoot-tip cuttings of Cherry Belle achieved a diameter greaterthan that of the radicle of the intact plant. Rooted cotyledonsof Cherry Belle cxrasionally produced small storage organs. Raphanus sativus, radish storage organ, root thickening, cambial activity     

Pollen-mediated gene flow in wheat (Triticum aestivum L.) in a semiarid field environment in Spain

Transgenic wheat (Triticum aestivum L.) varieties are being developed and field-tested in various countries. Concerns regarding gene flow from genetically modified (GM) crops to non-GM crops have stimulated research to estimate outcrossing in wheat prior to the release and commercialization of any transgenic cultivars. The aim is to ensure that coexistence of all types of wheat with GM wheat is feasible in accordance with current regulations. The present study describes the result of a field experiment under the semi-arid climate conditions of Madrid, Spain, at two locations (??La Canaleja?? and ??El Encin?? experimental stations) in Madrid over a 3-year period, from 2005 to 2007. The experimental design consisted of a 50?×?50?m wheat pollen source sown with wheat cultivars resistant to the herbicide chlortoluron (??Deganit?? and ??Castan?? respectively) and three susceptible receptor cultivars (??Abental??, ??Altria?? and ??Recital??) sown in replicated 1?×?1?m plots at different distances (0, 1, 3, 5, 10, 20, 40, 80 and 100?m) and four directions. Outcrossing rates were measured as a percentage of herbicide-resistant hybrids using an herbicide-screening assay. Outcrossing was greatest near the pollen source, averaging 0.029?% at 0?m distance at ??La Canaleja?? and 0.337?% at ??El Encin??, both below the 0.9?% European Union regulated threshold, although a maximum outcrossing rate of 3.5?% was detected in one recipient plot. These percentages declined rapidly as the distance increased, but hybrids were detected at different rates at distances of up to 100?m, the maximum distance of the experiment. Environmental conditions, as drought in 2004?C2005 and 2005?C2006, may have influenced the extent of outcrossing. These assays carried out in wheat under semi-arid conditions in Europe provide a more complete assessment of pollen-mediated gene flow in this crop.     

Progress of infection by Erysiphe graminis on fungicide-treated and untreated barley

Tridemorph-treated and untreated barley plants wre grown either in separate growth rooms or together. They were inoculated either with a sensitive or a tolerant isolate, and the progress of mildew was recorded. Comparisons were made between the rates of progress of sensitive and tolerant isolates on separated and unseparated fungicide treatments. Results suggested that interactions took place between pathogen populations on adjacent treated and untreated plants. Barley cv. Golden Promise was sown in plots made up of two adjacent fungicide treatments. Triadimefon, triforine, tridemorph and ethirimol were paired with each other and with untreated crops in all combinations. The progress of mildew on each plot was recorded, and differences were found between similar fungicide treatments from different plot pairs. The likelihood of interactions between mildew populations exposed in the field to different fungicide treatments is discussed.     

Control of K+ (Rb+) influx and transport with changed internal K+ concentration and age in two varieties of barley

The influx of Rb⁺ into the roots of two barley varieties (Hordeum vulgare L. cv. Salve and cv. Ingrid) from a K⁺-free ⁸⁶Rb-labelled nutrient solution with 2.0 mM Rb⁺, was checked at intervals from day 6 to day 18. The control plants were continuously grown in complete nutrient solution containing 5.0 mM K⁺, while two other groups of plants were grown in K⁺-free nutrient solution starting on day 6 and between day 6 and day 9, respectively. The pattern of Rb⁺ influx was similar for both varieties, although their efficiencies in absorbing Rb⁺ were different. The relationship between Rb⁺ influx and K⁺ concentration of the root could be interpreted in terms of negative feedback through allosteric control of uptake across the plasmalemma of the root cells. Hill plots were bimodal, but in the opposite direction. The Hill coefficients, reflecting the minimum number of interacting allosteric binding sites for K⁺ (Rb⁺), were low (≤–3.0). It is discussed whether the threshold value, that is the breaking point in the Hill plot, is indicative of a changed efficiency of transporting units for K⁺ (Rb⁺) transport to the xylem. Moreover, feedback regulation might be involved in transport of K⁺ between root and shoot. The variation in K⁺ concentrations in the roots and shoots of control plants were cyclic but in phase opposition despite an exponential growth. The average K⁺ concentration varied only slightly with age.     

Spatial and Temporal Assessment of Pollen- and Seed-Mediated Gene Flow from Genetically Engineered Plum Prunus domestica

Pollen flow from a 0.46 ha plot of genetically engineered (GE) Prunus domestica located in West Virginia, USA was evaluated from 2000–2010. Sentinel plum trees were planted at distances ranging from 132 to 854 m from the center of the GE orchard. Plots of mixed plum varieties and seedlings were located at 384, 484 and 998 m from the GE plot. Bee hives (Apis mellifera) were dispersed between the GE plum plot and the pollen flow monitoring sites. Pollen-mediated gene flow from out of the GE plum plot to non-GE plums under the study conditions was low, only occurring at all in 4 of 11 years and then in only 0.31% of the 12,116 seeds analyzed. When it occurred, gene flow, calculated as the number of GUS positive embryos/total embryos sampled, ranged from 0.215% at 132 m from the center of the GE plum plot (28 m from the nearest GE plum tree) to 0.033–0.017% at longer distances (384–998 m). Based on the percentage of GUS positive seeds per individual sampled tree the range was 0.4% to 12%. Within the GE field plot, gene flow ranged from 4.9 to 39%. Gene flow was related to distance and environmental conditions. A single year sample from a sentinel plot 132 m from the center of the GE plot accounted for 65% of the total 11-year gene flow. Spatial modeling indicated that gene flow dramatically decreased at distances over 400 m from the GE plot. Air temperature and rainfall were, respectively, positively and negatively correlated with gene flow, reflecting the effects of weather conditions on insect pollinator activity. Seed-mediated gene flow was not detected. These results support the feasibility of coexistence of GE and non-GE plum orchards.