Populations of Rhizoctonia solani in soil under crops in rotation with sugar beet

Using a soil debris isolation method, populations of Rhizoctonia solani were monitored over a 4 -yr period in four fields which were initially cropped to sugar beet and in which four areas of Rhizoctonia crown rot diseased beets (DA) and four areas of apparently healthy beets (AH) had been selected and precisely located. Soil from these areas was assayed during the subsequent crops, which included sugar beet, tomato, cucumber, maize and soybean. No significant differences in colony counts were found between the soils in DA and AH on any of 30 sampling dates. R. solani population counts were, in general, quite low, except under sugar beet and following tomato harvest. Areas of diseased beet and high R. solani soil populations that developed in subsequent sugar beet crops did not necessarily coincide with the previously selected diseased areas. High R. solani populations developed from parasitic activity on sugar beet or saprophytically on tomato crop residues. Of the other crops, both maize and soybean may have slightly increased the low R. solani residual populations in soil. The monitoring of R. solani populations in the season prior to, and during the early season of sugar beet cropping did not provide a basis for forecasting disease in fields or sites within fields. The initiation of disease patches in these sugar beet fields was therefore governed by factors other than inoculum density.     

Biocontrol of Rhizoctonia crown and root rot of sugar beet by binucleate Rhizoctonia spp. and Laetisaria arvalis

Two isolates of Laetisaria arvalis and 10 of binucleate Rhizoctonia spp. (BNR) from the Ohio sugar beet production area, were tested in the greenhouse and field for biocontrol of Rhizoctonia crown and root rot of sugar beet, caused by Rhizoctonia solani anastomosis group 2, type 2. L. arvalis was ineffective in standard greenhouse tests, and the single isolate used in the field was generally ineffective. Seven of 10 BNR isolates effectively controlled crown and root rot in greenhouse tests. Delayed application of biocontrol agents to plants 5 – 10 wk old was generally more effective than applications made at planting. A BNR isolate significantly reduced % plant loss and disease ratings and increased yield in a 1985 field test as compared with the control infested with R. solani alone. Two BNR isolates were effective in a 1986 field test and increased yields c. 22% in comparison to a L. arvalis treatment, which did not differ from the R. solani-infested control. The Ohio binucleate Rhizoctonia isolates appear to have considerable potential as applied biocontrol agents and may play a role in the natural ecology of R. solani in the sugar beet production area of Ohio.     

Evaluation of the state of the gene pool of natural populations dwelling in the fragmented landscape of Moscow and Moscow region (with special reference to brown frogs)

A system of urban ecological genetic monitoring of vertebrates has been developed for the first time in Russia and in the world. As a model, two species of brown frogs, Rana arvalis Nilss. and R. temporaria L. (16 populations, seven isozyme loci) were used. An evaluation of the gene pool state in urban frog populations has shown that the diversity in the Moscow frog populations was lower than that in natural populations (up to 80 and 50% in respectively R. arvalis and R. temporaria). Mean heterozygosities per locus were higher in large natural populations than in small urban isolates: in R. arvalis, these values were 0.16 and 0.06; in R. temporaria, 0.34 and 0.18, respectively. The number of polymorphic loci was also higher in natural populations than in the urban ones: 4 versus 2 in R. arvalis and 5 versus 4 in R. temporaria. Using superoxiddismutase as an example, fixation of different alleles of the same locus in different small isolates was shown. The gene pool condition of all but one urban populations of brown frog was evaluated as unsatisfactory, and that of the R. arvalis populations, as critical. These changes of the gene pool are explained mainly by gene drift accompanied by inbreeding, which was caused by human-induced fragmentation of the range and a decrease in population size of the species. The results of this study was employed in the development of the Moscow governmental program on restoration of the gene pools of vanishing animal species on specially protected natural urban territories. The series of works on long-term monitoring and assessment of the state of natural populations of model species in anthropogenic landscapes of Moscow and Moscow region has laid a foundation for a new branch of science, gene urbanology.     

Effect of Tillage System and Irrigation on Population Densities of Plant Nematodes in Field Corn

Soil populations of plant-parasitic nematodes were monitored bimonthly for 18 months in irrigated and nonirrigated corn plantings using four production systems: conventional and minimum tillage with crop residue returned and minimum tillage with 60% or 90% of previous corn crop residue removed. Populations of Meloidogyne incognita, Scutellonema brachyurum, Pratylenchus scribneri, and Paratrichodorus christiei varied among the tillage, nematicide, and irrigation treatments. Meloidogyne incognita and P. christiei populations were not significantly affected by tillage method, but S. brachyurum populations were highest during April 1981 and 1982 in minimum tillage treatments where crop debris was not removed. In contrast, S. brachyurum populations were lowest during the same period in minimum tillage plots where 90% of previous crop debris had been removed or where residues were incorporated with conventional tillage. Populations of P. scribneri were lowest in minimum tillage during August 1981 and April 1982. Regardless of tillage system, corn yields in all nonirrigated plots were increased during 1982 by application of carbofuran (2.24 kg a.i./ha). No yield increases were observed following nematicide application in 1981.     

Effects of Switchgrass (Panicum virgatum) Rotations with Peanut (Arachis hypogaea L.) on Nematode Populations and Soil Microflora

A 3-year field rotation study was conducted to assess the potential of switchgrass (Panicum virgatum) to suppress root-knot nematodes (Meloidogyne arenaria), southern blight (Sclerotium rolfsii), and aflatoxigenic fungi (Aspergillus sp.) in peanut (Arachis hypogaea L.) and to assess shifts in microbial populations following crop rotation. Switchgrass did not support populations of root-knot nematodes but supported high populations of nonparasitic nematodes. Peanut with no nematicide applied and following 2 years of switchgrass had the same nematode populations as continuous peanut plus nematicide. Neither previous crop nor nematicide significantly reduced the incidence of pods infected with Aspergillus. However, pod invasion by A. flavus was highest in plots previously planted with peanut and not treated with nematicide. Peanut with nematicide applied at planting following 2 years of switchgrass had significantly less incidence of southern blight than either continuous peanut without nematicide application or peanut without nematicide following 2 years of cotton. Peanut yield did not differ among rotations in either sample year. Effects of crop rotation on the microbial community structure associated with peanut were examined using indices for diversity, richness, and similarity derived from culture-based analyses. Continuous peanut supported a distinctly different rhizosphere bacterial microflora compared to peanut following 1 year of switchgrass, or continuous switchgrass. Richness and diversity indices for continuous peanut rhizosphere and geocarposphere were not consistently different from peanut following switchgrass, but always differed in the specific genera present. These shifts in community structure were associated with changes in parasitic nematode populations.     

Interrelationships of Rotylenchulus reniformis with Rhizoctonia solani on Cotton

The interrelationships between reniform nematode (Rotylenchulus reniformis) and the cotton (Gossypium hirsutum) seedling blight fungus (Rhizoctonia solani) were studied using three isolates of R. solani, two populations of R. reniformis at multiple inoculum levels, and the cotton cultivars Dehapine 90 (DP 90) and Dehapine 41 (DP 41). Colonization of cotton hypocotyl tissue by R. solani resulted in increases (P ≤ 0.05) in nematode population densities in soil and in eggs recovered from the root systems in both 40- and 90-day-duration experiments. Increases in soil population densities resulted mainly from increases in juveniles. Enhanced reproduction of R. reniformis in the presence of R. solani was consistent across isolates (1, 2, and 3) of R. solani and populations (1 and 2) and inoculum levels (0.5, 2, 4, and 8 individuals/g of soil) of R. reniformis, regardless of cotton cultivar (DP 90 or DP 41). Severity of seedling blight was not influenced by the nematode. Rhizoctonia solani caused reductions (P ≤ 0.05) in cotton growth in 40- and 90-day periods. Rotylenchulus reniformis reduced cotton growth at 90 days. The relationship between nematode inoculum levels and plant growth reductions was linear. At 90 days, the combined effects of these pathogens were antagonistic to plant growth.     

Suppression of sugar beet damping-off caused by Rhizoctonia solani using bacterial and fungal antagonists

Rhizoctonia damping-off caused by Rhizoctonia solani Kühn, is one of the most damaging sugar beet diseases. It causes serious economic damage wherever sugar beets are grown. Biological control is an efficient and environmentally friendly way to prevent damping-off disease. Suppression of damping-off disease caused by R. solani was carried out by four isolates of Bacillus subtilis (Ehrenberg) Cohn as well as three isolates of each of Trichoderma harzianum Rifai and Trichoderma hamatum (Bonord.) Bainier. The effect of Bacillus and Trichoderma isolates against R. solani was investigated in vitro and tested on sugar beet plants under greenhouse conditions. Isolates of Bacillus and Trichoderma were able to inhibit the growth of R. solani in dual culture. Furthermore, Trichoderma isolates gave high antagonistic effect than isolates of B. subtilis. Under greenhouse conditions, coating seeds by T. harzianum and B. subtilis separately, reduced seedling damping-off significantly. However, applications of T. harzianum increased the percentage of surviving plants more than B. subtilis in comparison to control. The obtained results indicate that T. harzianum and B. subtilis are very effective biocontrol agents that offer potential benefit in sugar beet damping-off and should be harnessed for further biocontrol applications.     

Density dependent growth in adult brown frogs Rana arvalis and Rana temporaria – A field experiment

In species with complex life cycles, density regulation can operate on any of the stages. In frogs there are almost no studies of density effects on the performance of adult frogs in the terrestrial habitat. We therefore studied the effect of summer density on the growth rate of adult frogs during four years. Four 30 by 30 m plots in a moist meadow were used. In early summer, when settled after post-breeding migration, frogs (Rana arvalis and Rana temporaria that have a very similar ecology and potentially compete) were enclosed by erecting a fence around the plots. Frogs were captured, measured, marked and partly relocated to create two high density and two low density plots. In early autumn the frogs were again captured and their individual summer growth determined. Growth effects were evaluated in relation to two density measures: density by design (high/low manipulation), and actual (numerical) density. R. arvalis in plots with low density by design grew faster than those in high density plots. No such effect was found for R. temporaria. For none of the species was growth related to actual summer density, determined by the Lincoln index and including the density manipulation. The result suggests that R. arvalis initially settled according to an ideal free distribution and that density had a regulatory effect (mediated through growth). The fact that there were no density effects on R. temporaria (and a significant difference in its response to that of R. arvalis) suggests it is a superior competitor to R. arvalis during the terrestrial phase. There were no density effects on frog condition index, suggesting that the growth rate modifications may actually be an adaptive trait of R. arvalis. The study demonstrates that density regulation may be dependent on resources in frogs' summer habitat.     

Effect of Population Dynamics of Pseudomonas cepacia and Paecilomyces lilacinus on Colonization of Polyfoam Rooting Cubes by Rhizoctonia solani

Suspensions of Pseudomonas cepacia (strain 5.5B) and Paecilomyces lilacinus (isolate 6.2F) were applied to polyfoam rooting cubes for control of stem rot of poinsettia caused by Rhizoctonia solani. The populations of antagonists and colonization of rooting cubes by R. solani were monitored during a 3-week period. Colonization of cubes by R. solani was reduced in cubes treated with P. cepacia, but the population of P. cepacia decreased by as much as 97% during the test period. Increased colonization by R. solani was correlated with a decline in population of P. cepacia. P. lilacinus was more persistent than P. cepacia in cubes, with only a 21% reduction observed during the 3-week period. Colonization of the P. lilacinus-treated cubes by R. solani was significantly less than colonization of infested controls. No correlation existed between population of P. lilacinus and colonization of cubes by R. solani.     

Role of Nematodes and Soil-borne Fungi in Cotton Stunt

The nematodes, Pratylenchus brachyurus, Trichodorus christiei, and T. porosus and the soil-borne fungi, Rhizoctonia solani, Pythium debaryanum, P. irregulare, P. ultimum, and Fusarium spp. were the pathogens most frequently found in the roots and rhizosphere of field-grown cotton (Gossypium hirsutum) showing "stunt" symptoms. Field-plot application of the nematicide D-D (l,2-dichloropropane, 1,3-dichloropropene) at 373.4 liter/ha (40 gal/A) significantly increased plant growth and yield. A fungicidal mixture of Dexon (p-dimethylaminobenzenediazo sodium sulfonate at 23.5 kg/ha (2l lb/A) and Terraclor (pentachloronitrobenzene at 25.2 kg/ha (22.5 lb/A) was phytotoxic, but combined nematicide/fungicide treatments were not. Greenhouse temperature-tank experiments in soils from two locations showed significantly improved root and shoot growth following methyl bromide fumigation at both 25 C and 18 C and more severe "stunt" at the lower temperature.     

Dynamics and management of the white potato cyst nematode Globodera pallida in commercial potato crops

Eight trials were conducted in commercial potato fields infested with the white potato cyst nematode (wPCN, Globodera pallida) and one in a field infested with the yellow PCN (yPCN, Globodera rostochiensis). Our aims were to produce data to validate and refine a computer‐based program (The Model) for the long‐term management of PCN, to determine nematicide effectiveness and to assess rates of PCN population decline between potato crops. Prior to planting, each farmer applied an overall nematicide treatment to his field, except for ten untreated plots that were widely spaced to encompass a range of PCN population densities. Each untreated plot was paired with a similar plot in the adjacent treated area and all plots were intensively sampled for PCN population densities at planting (P_i) and again at harvest (P_f) when tuber yields were determined. Four trials were re‐sampled 2–4 years later to determine PCN population decline rates. Regressions that form the basis of ‘The Model’ and described the relationship between P_i and tuber yield and PCN population density at harvest were fitted to the results from both the untreated and nematicide treated plots. These regressions also enabled us to estimate the yield potential at each site in the absence of PCN and showed that nematicide treatment generally did not increase yield potential and that both tuber yield and PCN multiplication decreased with increasing P_i. However, there were major differences between sites and cultivars. When untreated, the yield of cv. Maris Piper was hardly affected in a highly organic soil with P_i > 200 eggs g^?1 whereas the yield of partially resistant cv. Santé was decreased from a potential of c. 60 t ha^?1 to c. 20 t ha^?1 in a light silt with P_i = 20 egg g^?1 soil. Similarly, untreated wPCN multiplication rates at a low P_i ranged from 46‐fold to >100‐fold. Nematicide effectiveness was estimated from the regressions and, at several sites, yield was decreased despite nematicide treatment. Control of wPCN multiplication was even poorer. In only two of seven trials planted with susceptible cultivars was more than 50% control achieved – maximum populations in treated plots usually exceeded 250 eggs g^?1. Partially resistant Santé decreased the multiplication rate of wPCN in the two trials where it was planted. An alternative analysis using Genstat indicated that The Model tended to underestimate the maximum multiplication rate and overestimate the maximum population density. When four sites were re‐sampled 2–4 years after harvest the populations of wPCN had declined by between 15% and 33.5% per annum with a mean of 26% per annum. Modelling indicated that rotations longer than 8 years were required to control wPCN unless other effective control measures, such as growing a partially resistant cultivar, were used.     

Effects of Belonolaimus longicaudatus Management and Nitrogen Fertility on Turf Quality of Golf Course Fairways

Field experiments evaluated the effects of nematicide and fertility on performance of ‘Tifway 419’ bermudagrass parasitized by the sting nematode (Belonolaimus longicaudatus). Plot treatments were nontreated or nematicide (1,3-dichloropropene) treated combined with different nitrogen (N) fertilizer levels. Effects of treatments on numbers of B. longicaudatus and turf performance were compared. Nematicide consistently reduced numbers of B. longicaudatus, but fertilizer level had no effect on B. longicaudatus. Turf performance of nematicide-treated plots was improved compared with nontreated plots during both experiments. Increasing N fertilizer level improved turf performance in nematicide-treated plots in some cases, but had no effect on turf performance in nontreated plots in either experiment. Results suggest that increasing N fertilizer levels may not improve turf performance at sites infested with B. longicaudatus unless nematode management tactics are effective in reducing nematode densities.     

Nematicide Efficacy,Root Growth,and Fruit Yield in Drip-irrigated Pineapple Parasitized by Rotylenchulus reniformis

A 3-year field trial near Kunia, Oahu, Hawaii, was conducted to evaluate four nematicide treatments for efficacy against Rotylenchulus reniformis in drip-irrigated pineapple (Ananas comosus L. (Merr.)). The treatments were (A) preplant fumigation with 1,3-dichloropropene (1,3-D) (336 liter/ ha) and postplant drip application of fenamiphos (3.4 kg/ha) with restricted irrigation, (B) preplant 1,3-D only, weekly irrigation, (C) 1,3-D fenamiphos, weekly irrigation, and (D) postplant fenamiphos only, weekly irrigation. Fenamiphos was applied at 3-month intervals for 1 year after planting in three treatments. Although nematode populations increased in all treatments 1 year after planting, no differences in fruit yield were detected among treatments in the first (plant crop) harvest 19 months after planting. In the second (ratoon) crop (33 months after planting) significant yield differences, larger fruit size, and greater root biomass were obtained in the dual nematicide treatments. Root biomass increased continuously throughout the crop cycle, was greatest near the drip line, and showed a shallow depth distribution (30-40 cm). Rotylenchulus reniformis populations and fenamiphos concentrations were negatively correlated in soil profiles taken 13 months after planting. In the absence of postplant fenamiphos applications, nematode numbers were positively correlated with root biomass.     

Amphibians and squamate reptiles from the late Pleistocene of the “Caverne Marie-Jeanne” (Hastière-Lavaux,Namur, Belgium): Systematics,paleobiogeography, and paleoclimatic and paleoenvironmental reconstructions

Archeological sites usually provide important information about the past distribution of small vertebrate fauna, and by extension about past terrestrial environments and climate in which human activities took place. In this context, Belgium has an interesting location in northwestern Europe between the fully studied zooarcheological records of Germany and England. We present here the revision of the late Pleistocene (Marine Isotope Stages 3 and 2) collection of the “Caverne Marie-Jeanne” (Hastière-Lavaux, Namur), studied by Jean-Claude Rage in the 1970s and the revision of the whole “indeterminate” small vertebrate materials from the “Caverne Marie-Jeanne” stored in the Royal Belgian Institute of Natural Sciences (RBINS) Quaternary collections in search of more herpetofaunal remains. It is now by far the largest late Pleistocene collection at RBINS with more than 20,500 recognized bones of amphibians and reptiles and covering the last 60,000 years. The faunal list comprises two urodeles (Lissotriton gr. L. vulgaris and Salamandra salamandra), four anurans (Bufo gr. B. bufo-spinosus, Epidalea calamita, Rana temporaria and Rana cf. R. arvalis), three lizards (Lacerta cf. L. agilis, Zootoca vivipara and Anguis gr. A. fragilis), and three snakes (Natrix gr. N. natrix, Coronella austriaca, and Vipera berus). This study represents the first fossil record in Belgium for L. gr. L. vulgaris, R. arvalis, Z. vivipara, N. gr. N. natrix and C. austriaca. As a whole, this assemblage suggests a patchy humid landscape under colder and dryer climatic conditions in comparison with present ones. This study also underlines the necessity of a primary separation in larger taxonomical categories by the specialist itself.     

Effects of Rapeseed and Vetch as Green Manure Crops and Fallow on Nematodes and Soil-borne Pathogens

In a rapeseed-squash cropping system, Meloidogyne incognita race 1 and M. javanica did not enter, feed, or reproduce in roots of seven rapeseed cultivars. Both nematode species reproduced at low levels on roots of the third crop of rapeseed. Reproduction of M. incognita and M. javanica was high on squash following rapeseed, hairy vetch, and fallow. The application of fenamiphos suppressed (P = 0.05) root-gall indices on squash following rapeseed, hairy vetch, and fallow; and on Dwarf Essex and Cascade rapeseed, but not Bridger and Humus rapeseed in 1987. The incorporation of 30-61 mt/ha green biomass of rapeseed into the soil 6 months after planting did not affect the population densities of Criconemella ornata, M. incognita, M. javanica, Pythium spp., Rhizoctonia solani AG-4; nor did it consistently increase yield of squash. Hairy vetch supported larger numbers of M. incognita and M. javanica than rapeseed cultivars or fallow. Meloidogyne incognita and M. javanica survived in fallow plots in the absence of a host from October to May each year at a level sufficient to warrant the use of a nematicide to manage nematodes on the following susceptible crop.     

Role écologique deDigitalis purpurea dans la limitation naturelle des populations du puceron strié de la pomme de terreAulacorthum solani parAphidius urticae dans l'ouest de la France

Résumé En Bretagne les cultures de pommes de terre sont colonisées parAulacorthum solani,kltb,Macrosiphum euphorbiae thomas etMyzus persicae sulz. Lorsque le vol de contamination initiale par A.solani etM. persicae est de grande amplitude, le vol de dissémination est virtuellement absent, et inversement. Nous montrons que ceci est d? au très fort parasitisme qui affecte les populations dès leur installation sur les pommes de terre. En ce qui concerneA. solani, attaqué en particulier parAphidius urticae Hal. le r?le de la digitale en tant que producteur de pucerons et de parasites est mis en évidence. Le synchronisme entre la production de pucerons ailés et de parasites varie selon les biotopes et à ce titre la température para?t avoir une action prédominante.

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Summary In western France, the potato crops are regularly invaded byA. solani kltb,Myzus persicae sulz. andMacrosiphum euphorbiae thomas. Whenever the primary infestation by winged aphids is low, then the dissemination flight is relatively important and conversely (fig. 1). The reason is that aphidiids exert a good control as soon as aphid populations are building up. These parasites may be carried as eggs or young larvae in the alate aphids ofA. solani (table 1) and asD. purpurea constitutes one of its main winter host (A. solani is anholocyclic), the impcrtance of this plant was investigated as regards to aphid, parasite and hyperparasite production.Aphidius urticae hal-was the only parasite recorded so far with five hyperparasite species. On potato plants, too,A. urticae seems specifically concerned withA. solani otherwise attacked byAphidius picipes nees andAphidius ervi hal. It was shown some discrepancies between different biotopes as regards to the rate of parasitism at the same time (table 2) and attention is stressed on apparent differences between parasitization of apterous and winged instars (table 3), the importance of which is discussed regarding to the amount of winged invaders the foxglove may produce by the time the potato plants are shooting. Temperature appears to exert an important r?le in this respect.

     

Distribution and Morphology of Longidorus breviannulatus Norton &Hoffman, 1975 and Longidorus fragilis Thorne, 1974 (Nematoda: Longidoridae) from North America

In a survey of ecotypes for longidorids, primarily from the rhizosphere hardwood trees growing in sandy soil along stream banks, 828 soil samples were collected from 37 Arkansas counties in 1999-2001. Eight populations of Longidorus breviannulatus were identified from the Arkansas survey samples. A total of 19 populations from California, Illinois, Iowa, Kansas, Michigan, Nebraska, New Jersey, New York, and Wisconsin were identified from the collection of the second author. A few males were found in New York and Nebraska populations and are described herein. Seven populations of L. fragilis were identified in the Arkansas survey samples, and one population was found from Indiana. Four juvenile stages of L. fragilis are present, and data are given for them herein.     

Advances in molecular interactions on the Rhizoctonia solani-sugar beet pathosystem

Rhizoctonia solani is a soilborne pathogen with a broad host range. An anastomosis group (AG) system based on hyphal fusions has been established to distinguish between different R. solani subgroups in this species complex. Members of the AG2-2IIIB subgroup can cause serious problems in sugar beet production, resulting in Rhizoctonia root and crown rot. In this review, we summarize the current molecular advances in the R. solani sugar beet pathosystem. The draft genome of R. solani AG2-2IIIB has an estimated size of 56.02 Mb, larger than any of the R. solani AGs sequenced to date. The genome of AG2-2IIIB has been predicted to harbor 11,897 protein-encoding genes, including a high number of carbohydrate-active enzymes (CAZymes). The highest number of CAZymes was observed for polysaccharide lyase family 1 (PL-1), glycoside hydrolase family 43 (GH-43), and carbohydrate esterase family 12 (CE-12). Eleven single-effector candidates were predicted based on AG2-2IIIB genome data. The RsLysM, RsRlpA, and RsCRP1 genes were highly induced upon early-stage infection of sugar beet seedlings, and heterologous expression in Cercospora beticola and model plant species demonstrated their involvement in virulence. However, despite the progress achieved thus far on the molecular interactions in this pathosystem, many aspects remain to be elucidated, including the development of efficient transformation systems, important for functional studies, and the silencing of undesirable traits in the sugar beet crop.     

Nematicides Increase Grain Yields in Spring Wheat Cultivars and Suppress Plant-Parasitic and Bacterial-Feeding Nematodes

Grain yields of spring wheat (Triticum aestivum L. cvs. AC Barrie, AC Walton, AC Wilmot, Belvedere, Glenlea) in field plots over a 3-year period were increased (P < 0.001) by an average of 0.56 (25.1%) and 1.17 (52.5%) tonnes/ha in comparison to untreated check plots when aldicarb at 2.24 kg or fosthiazate at 13.5 a.i./ha, respectively, were broadcast and incorporated into the soil to suppress nematodes. The planned F test using orthogonal coefficients indicated that the mean response of grain yields to nematicide treatments of AC Barrie and Glenlea, which are grown primarily in the prairie provinces of Canada, was greater (48.5%) than the mean response of Belvedere, AC Walton, and AC Wilmot (33.7%), which are more common in the Maritime region of Canada (P < 0.001). Root lesion nematodes (primarily Pratylenchus penetrans) in wheat roots and in root zone soil at harvest were reduced by the nematicide applications (P < 0.001). Bacterial-feeding nematodes (primarily Diplogaster lheritieri (Maupas)) in root zone soil were also suppressed by fosthiazate (P < 0.01) but not by aldicarb. These data indicate that root lesion nematodes cause substantial yield losses in spring wheat in the Maritime region of Canada.     

Enhanced Heavy Metal Tolerance and Accumulation by Transgenic Sugar Beets Expressing Streptococcus thermophilus StGCS-GS in the Presence of Cd,Zn and Cu Alone or in Combination

Phytoremediation is a promising means of ameliorating heavy metal pollution through the use of transgenic plants as artificial hyperaccumulators. A novel Streptococcus thermophilus γ-glutamylcysteine synthetase-glutathione synthetase (StGCS-GS) that synthesizes glutathione (GSH) with limited feedback inhibition was overexpressed in sugar beet (Beta vulgaris L.), yielding three transgenic lines (s2, s4 and s5) with enhanced tolerance to different concentrations of cadmium, zinc and copper, as indicated by their increased biomass, root length and relative growth compared with wild-type plants. Transgenic sugar beets accumulated more Cd, Zn and Cu ions in shoots than wild-type, as well as higher GSH and phytochelatin (PC) levels under different heavy metal stresses. This enhanced heavy metal tolerance and increased accumulation were likely due to the increased expression of StGCS-GS and consequent overproduction of both GSH and PC. Furthermore, when multiple heavy metal ions were present at the same time, transgenic sugar beets overexpressing StGCS-GS resisted two or three of the metal combinations (50 μM Cd-Zn, Cd-Cu, Zn-Cu and Cd-Zn-Cu), with greater absorption in shoots. Additionally, there was no obvious competition between metals. Overall, the results demonstrate the explicit role of StGCS-GS in enhancing Cd, Zn and Cu tolerance and accumulation in transgenic sugar beet, which may represent a highly promising new tool for phytoremediation.