Evaluation of transgenic cotton varieties and a glyphosate application on seedling disease incidence

A study was conducted to determine whether stand densities of transgenic cotton (Gossypium hirsutum) varieties, with or without glyphosate, were similar to conventional varieties of the same lineage group in Georgia and Mississippi. Transgenic and conventional cotton varieties were placed into five lineage groups of related varieties and seedling disease was evaluated in three greenhouse tests and a field trial using Rhizoctonia solani AG-4. Seed vigor was determined by standard germination studies were conducted evaluating conventional and transgenic varieties of similar lineage. Results showed that no interactions occurred for the heights and dry weight data across treatments within the lineage groups in any of the experiments. No interactions were shown between stand densities at different inoculum rates and inoculated versus uninoculated pots (plots). Across all greenhouse studies, stand counts of PM 1220 were similar to the transgenic varieties PM 1220 RR and PM 1220 B/RR with or without a glyphosate application. In the field trial, PM 1220 B/RR + glyphosate had significantly lower stands than all other treatments expect PM 1220 RR (no glyphosate treatment) prior to and after glyphosate application. Stand densities for varieties within the lineage group DPL 5415 were also inconsistent when compared between the greenhouse and field trials with no apparent trends occurring. However, the Coker 312 varieties containing glyphosate tolerance had consistently lower stand counts compared to the conventional variety of Coker 312 but only during the greenhouse studies. Seed germination of Coker 312 could not be correlated with either the greenhouse or field trial data. In general, the commercially available varieties such as PM 1220, DPL 5690, DPL 5415, and DPL 50 with glyphosate tolerance had similar stand count, height, and dry weight data when compared to the conventional varieties from the same lineage group regardless of a glyphosate application. When differences did occur, no consistent trends could be determined within these four lineage groups.     

Susceptibility and tolerance in hybrid and pure‐line rice varieties to herbivore attack: biomass partitioning and resource‐based compensation in response to damage

Hybrid rice has been noted for its susceptibility to insects and diseases compared to pure‐line (conventional) rice varieties. We investigated herbivory by Nilaparvata lugens, Sogatella furcifera and Scirpophaga incertulas on replicated three‐line hybrid sets (parental and hybrid lines) in field and greenhouse experiments. In a field experiment, caterpillar densities and stemborer damage was similar among hybrid and parental lines. In field and greenhouse experiments, the cytoplasmic male sterile (CMS)‐lines and maintainer lines had higher densities of planthoppers (including N. lugens and S. furcifera) than restorer or hybrid lines likely because of their wild abortive CMS‐lineage. High nitrogen levels increased plant mortality due to N. lugens, but often reduced mortality from S. furcifera and S. incertulas: this was similar between hybrid and pure‐line varieties. The hybrids were generally more tolerant of herbivory (lower biomass reductions per unit weight of insect) than the inbred parental lines. The addition of nitrogen to both the hybrid and pure‐line varieties had contrasting effects on tolerance depending on the nature of the attacking insect: fertiliser increased tolerance to S. furcifera (lower losses of yield and shoot biomass per mg insect) and S. incertulas (lower yield, shoot and root biomass loss) but fertiliser reduced tolerance to N. lugens (higher loss of root biomass and no effects on yield and shoot biomass loss). Our results indicate that hybrid rice is not physiologically more susceptible to herbivores than are pure‐line varieties even under high nitrogen conditions, but does have higher tolerance to insect damage.     

Metal uptake by iron-efficient and inefficient oats

Metal uptake by oats depending on plant responses to Fe-deficiency stress was investigated. Coker 227 oats classified as Fe-efficient and TAM 0–312 oats as Fe-inefficient cultivars (Hopkins et al., 1992) were grown either alone or in combination in three sandy soils using a pot experiment. These soils were from a field trial with sludge-borne metals applications leading to an increased metal content. Plant shoots were harvested one month after growth. Because soil pH increased from 5.4 to 6.8, shoot Fe level decreased in the Fe-inefficient TAM 0–312 oats compared to Coker 227 oats when plants were grown alone. In combination, TAM 0–312 oats had a negative impact on the availability of Fe in the Fe-efficient Coker 227 oats. Especially, Coker 227 and TAM 0–312 shoots showed chlorosis in mixed culture with high Zn and Mn content in the soil (soil B). However, Fe content in TAM 0–312 shoots in mixed culture did not increase compared to monoculture in all soils. In metal-contaminated soils, TAM 0–312 oats grown alone obtained less Zn and Cd than Coker 227 oats. Additionally at soil pH 6.8, shoot Ni and Mn levels were also lower in TAM 0–312 oats than in Coker 227 oats. Shoot Zn, Cd, and Ni levels decreased in Coker 227 oats from mixed cultures, and were not different compared to those in TAM 0–312 oats. Cu uptake was similar in all treatments except for the mixed culture in soil B. Coker 227 oats have been found to release a phytosiderophore whereas TAM 0–312 did not (Brown et al., 1991). Results indicated that phytosiderophores may lead to a higher Zn, Cd and Ni supply in the rhizosphere of Coker 227 oats and to higher metal contents in their shoots than in TAM 0–312 oats which did not activate such mechanisms.     

Co‐expression of GR79 EPSPS and GAT yields herbicide‐resistant cotton with low glyphosate residues

Glyphosate‐resistant (GR) crops have been adopted on a massive scale by North and South American farmers. Currently, about 80% of the 120 million hectares of the global genetically modified (GM) crops are GR crop varieties. However, the adoption of GR plants in China has not occurred at the same pace, owing to several factors including, among other things, labour markets and the residual effects of glyphosate in transgenic plants. Here, we report the co‐expression of codon‐optimized forms of GR79 EPSPS and N‐acetyltransferase (GAT) genes in cotton. We found five times more resistance to glyphosate with 10‐fold reduction in glyphosate residues in two pGR79 EPSPS‐pGAT co‐expression cotton lines, GGCO2 and GGCO5. The GGCO2 line was used in a hybridization programme to develop new GR cottons. Field trials at five locations during three growing seasons showed that pGR79‐pGAT transgenic cotton lines have the same agronomic performance as conventional varieties, but were USD 390‐495 cheaper to produce per hectare because of the high cost of conventional weed management practices. Our strategy to pyramid these genes clearly worked and thus offers attractive promise for the engineering and breeding of highly resistant low‐glyphosate‐residue cotton varieties.     

Transgenic cotton resistant to herbicide bialaphos

Resistance to bialaphos, a non-selective herbicide, was intro duced into cotton through genetic engineering. A gene encoding phosphinothric in acetyltransferase (bar) from Streptomyces hygroscopicus was inserted into elite varieties of cotton through particle bombardment. Based on the marker gene, -glucuronidase (gus) expression, a total of 18 Pima (Gossypium barbadense), 45 DP50 (G. hirsutum L.), 20 Coker 312 (G. hirsutum) and 2 El Dorado (G. hirsutum) transgenic plants were recovered. Integration of the bar gene into cotton genomic DNA was confirmed by Southern blot analysis and gene expression was confirmed by northern blot and enzyme assays. Herbicide (Basta®) tolerance up to 15 000 ppm was demonstrated in greenhouse trials. The newly introduced herbicide tolerance trait is inherited in a Mendelian fashion in the progenies of germline transformants. This study demonstrates the potential for particle bombardment to introduce commerically important genes directly into elite varieties of cotton. This mode of gene transfer can expedite the introduction of transgenic cotton products into world markets     

转Bt基因棉花及其受体品种主要挥发性物质的测定

应用顶空进样气质联机系统（Headspace-GC-MS)测定了转Bt基因棉花及其对照亲本主要挥发性物质。结果表明棉花营养器官和繁殖器官的主要挥发性物质的差异,棉花植株现蕾期前,叶片中挥发性物质以α-蒎烯为主,而现蕾后,蕾、花和铃中主要以β-月桂烯为主。研究初步发现,外源Bt杀虫蛋白表达对棉花自身主要挥发性物质的合成不会造成不利影响。     

Efficient particle bombardment-mediated transformation of Cuban soybean (INCASoy-36) using glyphosate as a selective agent

Soybean is highly affected by weeds in tropical countries, causing significant losses in yields. Transgenic herbicide resistant soybeans have been produced in a limited number of varieties and parental lines. This study was conducted to obtain glyphosate herbicide resistant transgenic soybean plants through particle bombardment of embryonic axes in a Cuban variety. Shoot regeneration in 25 mg/L of glyphosate occurred within a short period and plantlets developed roots in a medium without selection pressure, which favored the in vitro growth of plants at a transformation frequency of 3.1–6.0?%. Expression and integration of the cp4epsps gene was confirmed in the progeny by an immune-detection assay, PCR and Southern blot. All greenhouse evaluated transgenic soybean lines (T₁) displayed tolerance to 1.25 Kg/ha of glyphosate. Growth and seed development of transformed plants was similar to untransformed plants. The regeneration procedure using embryonic axes combined with the efficient selection of shoots in glyphosate enabled the production of transgenic plants of this Cuban genotype, showing high tolerance to the herbicide, good efficiency and reproducibility.     

Glyphosate affects photosynthesis in first and second generation of glyphosate-resistant soybeans

The crop area planted to conventional soybeans has decreased annually while that planted to glyphosate-resistant (RR) soybean has drastically increased mainly due to the wide adoption of glyphosate in current weed management systems. With the extensive use of glyphosate, many farmers have noted visual plant injury in RR soybean varieties after glyphosate application. A new generation designated as “second generation—RR2” has been recently developed and these RR2 cultivars already are commercially available for farmers and promoted as higher yielding relative to the previous RR cultivars. However, little information is currently available about the performance of RR2 soybean beyond commercial and farmer testimonial data. Thus, an evaluation of different glyphosate rates applied in different growth stages of the first and second generation of RR soybeans, revealed a significant decrease in photosynthesis. In general, increased glyphosate rate and late applications (V6) pronounced decrease photosynthetic parameters and consequently decreased in leaf area and shoot biomass production. In contrast, low rate and early applications were less damage for the RR soybean plants, suggesting that with early applications (V2), plants probably have more time to recover from glyphosate or its metabolites effects regarding late applications.     

Cell suspension culture-mediated incorporation of the rice bel gene into transgenic cotton

Cotton plants engineered for resistance to the herbicides, glyphosate or glufosinate have made a considerable impact on the production of the crop worldwide. In this work, embryogenic cell cultures derived from Gossypium hirsutum L. cv Coker 312 hypocotyl callus were transformed via Agrobacterium tumefaciens with the rice cytochrome P450 gene, CYP81A6 (bel). In rice, bel has been shown to confer resistance to both bentazon and sulfanylurea herbicides. Transformed cells were selected on a liquid medium supplemented alternately or simultaneously with kanamycin (50mg/L) and bentazon (4.2 μmol). A total of 17 transgenic cotton lines were recovered, based on the initial resistance to bentazon and on PCR detection of the bel transgene. Bel integration into the cotton genome was confirmed by Southern blot and expression of the transgene was verified by RT-PCR. In greenhouse and experimental plot trials, herbicide (bentazon) tolerance of up to 1250 mg/L was demonstrated in the transgenic plants. Transgenic lines with a single copy of the bel gene showed normal Mendelian inheritance of the characteristic. Importantly, resistance to bentazon was shown to be stably incorporated in the T1, T2 and T3 generations of self-fertilised descendents and in plants outcrossed to another upland cotton cultivar. Engineering resistance to bentazon in cotton through the heterologous expression of bel opens the possibility of incorporating this trait into elite cultivars, a strategy that would give growers a more flexible alternative to weed management in cotton crops.     

Effects of Heterodera glycines and Meloidogyne incognita on Early Growth of Soybean

Greenhouse and field microplot studies were conducted to compare soybean shoot and root growth responses to root penetration by Heterodera glycines (Hg) and Meloidogyne incognita (Mi) individually and in combination. Soybean cultivars Centennial (resistant to Hg and Mi), Braxton (resistant to Mi, susceptible to Hg), and Coker 237 (susceptible to Hg and Mi) were selected for study. In the greenhouse, pot size and number of plants per pot had no effect on Hg or Mi penetration of Coker 237 roots; root weight was higher in the presence of either nematode species compared with the noninoculated controls. In greenhouse studies using a sand or soil medium, and in field microplot studies, each cultivar was grown with increasing initial population densities (Pi) of Hg or Mi. Interactions between Hg and Mi did not affect early plant growth or number of nematodes penetrating roots. Root penetration was the only response related to Pi. Mi penetration was higher in sand than in soil, and higher in the greenhouse than in the field, whereas Hg penetration was similar under all conditions. At 14 days after planting, more second-stage juveniles were present in roots of susceptible than in roots of resistant plants. Roots continued to lengthen in the greenhouse in the presence of either Mi or Hg regardless of host genotype, but only in the presence of Mi in microplots; otherwise, responses in field and greenhouse studies were similar and differed only in magnitude and variability.     

Expression of the Arabidopsis vacuolar H+‐pyrophosphatase gene (AVP1) improves the shoot biomass of transgenic barley and increases grain yield in a saline field

Cereal varieties with improved salinity tolerance are needed to achieve profitable grain yields in saline soils. The expression of AVP1, an Arabidopsis gene encoding a vacuolar proton pumping pyrophosphatase (H⁺‐PPase), has been shown to improve the salinity tolerance of transgenic plants in greenhouse conditions. However, the potential for this gene to improve the grain yield of cereal crops in a saline field has yet to be evaluated. Recent advances in high‐throughput nondestructive phenotyping technologies also offer an opportunity to quantitatively evaluate the growth of transgenic plants under abiotic stress through time. In this study, the growth of transgenic barley expressing AVP1 was evaluated under saline conditions in a pot experiment using nondestructive plant imaging and in a saline field trial. Greenhouse‐grown transgenic barley expressing AVP1 produced a larger shoot biomass compared to null segregants, as determined by an increase in projected shoot area, when grown in soil with 150 mm NaCl. This increase in shoot biomass of transgenic AVP1 barley occurred from an early growth stage and also in nonsaline conditions. In a saline field, the transgenic barley expressing AVP1 also showed an increase in shoot biomass and, importantly, produced a greater grain yield per plant compared to wild‐type plants. Interestingly, the expression of AVP1 did not alter barley leaf sodium concentrations in either greenhouse‐ or field‐grown plants. This study validates our greenhouse‐based experiments and indicates that transgenic barley expressing AVP1 is a promising option for increasing cereal crop productivity in saline fields.     

Assessment of gene flow from glyphosate-resistant transgenic soybean to conventional soybean in China

Glyphosate-resistant (GR) transgenic soybean has never been cultivated commercially in China. It is essential to develop the separation measures required to prevent out-crossing between GR and conventional soybean (Glycine max (L.) Merr.) by characterizing the transgene flow before GR soybean is released. In this study, the transgene flow from a GR transgenic soybean AG5601 to conventional soybeans was characterized. First, natural out-crossing rate was evaluated using 36 conventional soybean varieties interplanted with GR soybean AG5601 transformed with a cp4 EPSPS gene conferring the resistance to herbicide glyphosate in the field in 2007 and 2008 in China. Second, drift distance of cp4 EPSPS gene from GR soybean AG5601 to soybean cv. Zhonghuang13 was evaluated using the progenies harvested from eight directions at different distance. Third, the relationship of gene flow of GR soybean AG5601 with flowering synchronization days or insect pollinators of each variety was analyzed using regression analysis. Thirty-two of 36 tested conventional soybean varieties had surviving progenies after two times of sprays of glyphosate, and 49 of 41,679 progenies were verified to be glyphosate-tolerant heterozygous offspring. The out-crossing rates in positive varieties (having surviving offspring after two times of sprays of glyphosate) ranged from 0.039 to 0.934 %. The farthest distance (drift distance) between soybean AG5601 and cv. Zhonghuang13 at which out-pollinating was still able to be observed was 15 m, with an out-crossing rate of 0.012 %. Regression analysis showed that there was a positive relationship between cross-pollination frequency and flowering synchronization days or pollinator insects. Therefore, when GR soybean is released to the field, it should be critically separated with the conventional soybean in space and cultivation time with efficient insect control during flowering.     

Identification of a novel elite genotype for in vitro culture and genetic transformation of cotton

Hypocotyls of cotton (Gossypium hirsutum L.) cultivars cv. YZ-1, Coker 312 and Coker 201 were inoculated on Murashige and Skoog callus induction medium. YZ-1 exhibited a very high regeneration potential, with 81.9 % of the explants inoculated differentiated into embryogenic callus within 8–10 weeks. During the process of callus maintenance (subculture for 1 to 3 years), the total embryos number in Coker 312 and Coker 201 calli dropped sharply, and the percentage of embryo germination decreased. On the contrary, the callus of YZ-1 consistently maintains a high frequency of plant regeneration after long-time subculture. Transgenic kanamycin-resistant calli of Coker 201 partially lost the ability of somatic embryogenesis and plant regeneration. The stress produced by the transformation procedure slightly affected somatic embryogenesis and plant regeneration of YZ-1, which showed minimum loss of plant regeneration ability.     

Effect of Bt-cotton expressing Cry1A(c) on the survival and fecundity of two hymenopteran parasitoids (Braconidae, Encyrtidae) in the laboratory

We examined the effect of Bt-cotton (Event 531) plants expressing the Bacillus thuringiensis δ-endotoxin CryIA(c) on two hymenopteran endoparasitoids, Cotesia marginiventris and Copidosoma floridanum. In the laboratory, parasitized and unparasitized Pseudoplusia includens larvae were reared on foliage from a conventional soybean cultivar (Pioneer 97B61), a conventional cotton cultivar (DPL 5415), or a Bt-cotton cultivar (NuCotn 33B). C. marginiventris developed significantly faster within P. includens larvae feeding on Pioneer 97B61 and DPL 5415 compared to those feeding on NuCotn 33B. C. marginiventris that developed inside P. includens larvae feeding on NuCotn 33B suffered reduced longevity, and females had fewer ova. NuCotn 33B also affected the growth and development of P. includens parasitized with C. floridanum and life history parameters of adult C. floridanum. Parasitized and unparasitized P. includens developed more slowly when they were fed NuCotn 33B and the prepupae weighed less. Survival of parasitized and unparasitized P. includens was lower when larvae were fed NuCotn 33B and some evidence points to higher susceptibility of parasitized caterpillars to intoxication by NuCotn 33B. Fewer C. floridanum adults emerged from hosts fed NuCotn 33B, but pupal weight and adult longevity were unaffected. Analysis comparing the two experiments conducted with C. floridanum suggests that older NuCotn 33B plants (90–120 days after planting) may affect parasitoid development and adult survival less than younger NuCotn 33B plants (60–90 days after planting). Feeding on NuCotn 33B by P. includens affected the survival and development of the two hymenopteran endoparasitoids studied here, and the degree of the effect was similar to that observed with natural resistance found in soybean plants. It remains to be determined if the effects demonstrated here are less than, equal to, or greater than the impact of conventional insecticide applications used in conventional, non-transgenic, cotton.     

Herbicide-resistant Acala and Coker cottons transformed with a native gene encoding mutant forms of acetohydroxyacid synthase

Herbicide-resistant transgenic cotton (Gossypium hirsutum L.) plants carrying mutant forms of a native acetohydroxyacid synthase (AHAS) gene have been obtained by Agrobacterium and biolistic transformation. The native gene, A19, was mutated in vitro to create amino acid substitutions at residue 563 or residue 642 of the precursor polypeptide. Transformation with the mutated forms of the A19 gene produced resistance to imidazolinone and sulfonylurea herbicides (563 substitution), or imidazolinones only (642 substitution). The herbicide-resistant phenotype of transformants was also manifested in their in vitro AHAS activity. Seedling explants of both Coker and Acala cotton varieties were transformed with the mutated forms of the A19 gene using Agrobacterium. In these experiments, hundreds of transformation events were obtained with the Coker varieties, while the Acala varieties were transformed with an efficiency about one-tenth that of Coker. Herbicide-resistant Coker and Acala plants were regenerated from a subset of transformation events. Embryonic cell suspension cultures of both Coker and Acala varieties were biolistically transformed at high frequencies using cloned cotton DNA fragments carrying the mutated forms of the A19 gene. In these transformation experiments the mutated A19 gene served as the selectable marker, and the efficiency of selection was comparable to that obtained with the NPT II gene marker of vector Bin 19. Using this method, transgenic Acala plants resistant to imidazolinone herbicides were obtained. Southern blot analyses indicated the presence of two copies of the mutated A19 transgene in one of the biolistically transformed R₀ plants, and a single copy in one of the R₀ plants transformed with Agrobacterium. As expected. progeny seedlings derived from outcrosses involving the R₀ plant transformed with Agrobacterium segregated in a 1:1 ratio with respect to herbicide resistance. The resistant progeny grew normally after irrigation with 175 g/l of the imidazolinone herbicide imazaquin, which is five times the field application rate. In contrast, untransformed sibling plants were severely stunted.Abbreviations AHAS acetohydroxyacid synthase - CaMV cauliflower mosaic virus - ELISA enzyme linked immunosorbent assay - FW fresh weight - GUS -glucuronidase - IC₅₀ herbicide concentration that produces a 50% reduction in the fresh weight growth of cells - NAA -naphthaleneacetic acid - NPT II neomycin phosphotransferase II - MS Murashige and Skoog (1962)     

Phenolic compounds and somatic embryogenesis in cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.)

Studies of phenolic compounds were performed during cell suspension cultures in relation with the induction of embryogenic structures in two cultivars of cotton. Coker 312 produced embryogenic structures, unlike R405-2000 which was found to be a non-embryogenic cultivar. Embryogenesis induction in Coker 312 was strongly linked to a higher content of caffeic, ferulic and salicylic acids and to the appearance of p-coumaric acid, benzoic acid, trans-resveratrol, catechin and naringenin.     

Enhancement of Reproductive Heat Tolerance in Plants

Comparison of average crop yields with reported record yields has shown that major crops exhibit annual average yields three- to seven-fold lower than record yields because of unfavorable environments. The current study investigated the enhancement of pollen heat tolerance through expressing an Arabidopsis thaliana heat shock protein 101 (AtHSP101) that is not normally expressed in pollen but reported to play a crucial role in vegetative thermotolerance. The AtHSP101 construct under the control of the constitutive ocs/mas ‘superpromoter’ was transformed into cotton Coker 312 and tobacco SRI lines via Agrobacterium mediated transformation. Thermotolerance of pollen was evaluated by in vitro pollen germination studies. Comparing with those of wild type and transgenic null lines, pollen from AtHSP101 transgenic tobacco and cotton lines exhibited significantly higher germination rate and much greater pollen tube elongation under elevated temperatures or after a heat exposure. In addition, significant increases in boll set and seed numbers were also observed in transgenic cotton lines exposed to elevated day and night temperatures in both greenhouse and field studies. The results of this study suggest that enhancing heat tolerance of reproductive tissues in plant holds promise in the development of crops with improved yield production and yield sustainability in unfavorable environments.     

Efficacy of transgenic cotton containing a cry1Ac gene from Bacillus thuringiensis against Helicoverpa armigera (Lepidoptera: Noctuidae) in northern China

NuCOTN 33B, a Bt transgenic variety of upland cotton (Gossypium hirsutum L.) expressing the insecticidal protein Cry1Ac from Bacillus thuringiensis Berliner sp. kurstaki, was evaluated for resistance to Helicoverpa armigera (Hübner) during 1998-2000 in northern China. The results indicated that there was no significant difference in egg densities between NuCOTN 33B and three nontransgenic varieties (DP5415, Zhongmian12, and Shiyuan321) during the season, although the survival of larvae on NuCOTN 33B seemed significantly reduced. High larval densities observed on non-Bt cotton appeared in great contrast to the low larval populations observed on NuCOTN 33B plants during the seasons. In an environment without insecticide sprays, the annual ginned cotton yields in NuCOTN 33B plots, ranging from 1391.17 to 1511.35 kg/ha, were significantly higher than those in non-Bt cotton (340.34-359.58 kg/ha). These high levels of field efficacy for NuCOTN 33B against H. armigera in northern China may pave the way for reduced pesticide applications and an expansion of alternative pest-control strategies.     

A Comparative Risk Assessment of Genetically Engineered,Mutagenic, and Conventional Wheat Production Systems

Wheat (Triticum aestivum L.) varieties produced using modern biotechnologies, such as genetic engineering and mutagenic techniques, have lagged behind other crop species, but are now being developed and, in the case of mutagenic wheat, commercially grown around the world. Because these wheat varieties have emerged recently, there is a unique opportunity to assess comparatively the potential environmental risks (human health, ecological, and livestock risks) associated with genetically engineered, mutagenic, and conventional wheat production systems. Replacement of traditional herbicides with glyphosate in a glyphosate-tolerant (genetically engineered) wheat system or imazamox in an imidazolinone-tolerant (mutagenic) wheat system may alter environmental risks associated with weed management. Additionally, because both systems rely on plants that express novel proteins, the proteins and plants themselves may impose risks. The purpose of our study was to examine comparatively the multiple aspects of risk associated with different wheat production systems in the US and Canada using the risk assessment paradigm. Specifically, we used tier 1 quantitative and qualitative risk assessment methods to compare specific environmental risks associated with the different wheat production systems. Both glyphosate and imazamox present lower human health and ecological risks than many other herbicides associated with conventional wheat production systems evaluated in this study. The differences in risks were most pronounced when comparing glyphosate and imazamox to herbicides currently with substantial market share. Current weight-of-evidence suggests that the transgenic CP4 EPSPS protein present in glyphosate-tolerant wheat poses negligible risk to humans, livestock, and wildlife. Risk for mutated AHAS protein in imidazolinone-tolerant wheat most likely would be low, but there are not sufficient effect and exposure data to adequately characterize risk. Environmental risks for herbicides were more amenable to quantitative assessments than for the transgenic CP4 EPSPS protein and the mutated AHAS protein.     

Effect of pyramiding Bt and CpTI genes on resistance of cotton to Helicoverpa armigera (Lepidoptera: Noctuidae) under laboratory and field conditions

Transgenic cotton (Cossypium hirsutum L.) varieties, adapted to China, have been bred that express two genes for resistance to insects, the CrylAc gene from Bacillus thuringiensis (Berliner) (Bt), and a trypsin inhibitor gene from cowpea (CpTI). Effectiveness of the double gene modification in conferring resistance to cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), was studied in laboratory and field experiments. In each experiment, performance of Bt+CpTI cotton was compared with Bt cotton and to a conventional nontransgenic variety. Larval survival was lower on both types of transgenic variety, compared with the conventional cotton. Survival of first-, second-, and third-stage larvae was lower on Bt+CpTI cotton than on Bt cotton. Plant structures differed in level of resistance, and these differences were similar on Bt and Bt + CpTI cotton. Likewise, seasonal trends in level of resistance in different plant structures were similar in Bt and Bt+CpTI cotton. Both types of transgenic cotton interfered with development of sixth-stage larvae to adults, and no offspring was produced by H. armigera that fed on Bt or Bt+CpTI cotton from the sixth stage onward. First-, second-, and third-stage larvae spent significantly less time feeding on transgenic cotton than on conventional cotton, and the reduction in feeding time was significantly greater on Bt+CpTI cotton than on Bt cotton. Food conversion efficiency was lower on transgenic varieties than on conventional cotton, but there was no significant difference between Bt and Bt+CpTI cotton. In 3-yr field experimentation, bollworm densities were greatly suppressed on transgenic as compared with conventional cotton, but no significant differences between Bt and Bt+CpTI cotton were found. Overall, the results from laboratory work indicate that introduction of the CpTI gene in Bt cotton raises some components of resistance in cotton against H. armigera, but enhanced control of H. armigera under field conditions, due to expression of the CpTI gene, was not demonstrated.