Bt Hybrids Research Articles

Desenvolvimento de Helicoverpa spp. em milho Bt com expressão de diferentes proteínas

Resumo: O objetivo deste trabalho foi avaliar os aspectos biológicos de Helicoverpa zea e Helicoverpa armigera (Lepidoptera: Noctuidae) em híbridos de milho com expressão de diferentes proteínas. Foram avaliadas as proteínas Cry1F, Cry1A(b), Cry1A.105 + Cry2Ab2 e Vip3A e seus respectivos isogênicos convencionais. As larvas foram alimentadas com espiguetas de milho Bt e convencional, trocadas a cada dois dias. Os parâmetros avaliados foram: sobrevivência 48 horas após eclosão, sobrevivência larval, peso de larvas e de pupas, período de desenvolvimento larval e período pré-imaginal. Observou-se efeito significativo da interação entre evento de milho Bt e espécie de Helicoverpa para todas as variáveis biológicas avaliadas. Larvas de H. armigera apresentaram maior sobrevivência 48 horas após eclosão em milho expressando a proteína Cry1F e a Vip3 em relação a H. zea. O período letal foi maior em H. armigera do que em H. zea, mas, em milho com expressão da proteína Cry1A(b), foi quatro vezes menor. Não houve sobrevivente para ambas as espécies de Helicoverpa em nenhum dos híbridos Bt avaliados. Nos isogênicos convencionais, o índice de adaptação de H. armigera foi superior ao de H. zea, o que indica maior facilidade de adaptação ao ambiente dessa espécie.

Survival and development of spotted bollworm, Earias vittella (Fabricius) (Lepidoptera: Nolidae) on different transgenic Bt and isogenic non-Bt cotton genotypes

Four Bt cotton hybrids, each with one of four different events, viz., MRC 6301 Bt (cry1Ac gene), JKCH 1947 Bt (modified cry1Ac gene), NCEH 6R Bt (fusion cry1Ac/cry1Ab gene) and MRC 7017 Bollgard II (cry1Ac and cry2Ab genes) were compared for survival and development of Earias vittella (Fabricius) along with their isogenic non-Bt genotypes. None of the neonates were able to complete the larval period and reach pupal stage on squares of 90, 120 and 150 days old crop of all Bt hybrids. Likewise, on bolls also, zero per cent larval survival was observed in all Bt hybrids except JKCH 1947 Bt where 0.67 per cent larvae could manage to reach pre-pupal stage at 120 and 150 days old crop but failed to form cocoon and enter pupal stage. The surviving larva took more development time (3.7 to 5.4 days) as compared to larvae fed on bolls of JKCH 1947 non-Bt. The average survival period (ASP) of larvae was in order of 150 > 120 > 90 days old crop among the crop ages; JKCH 1947 Bt > MRC 6301 Bt > NCEH 6 R Bt > MRC 7017 Bollgard II among Bt hybrids; and bolls > squares between fruiting bodies. However, reverse was true for speed index of toxic effect. The concentration of Cry toxin varied significantly in squares and bolls and also among the crop ages. The amount of Cry toxin in squares and bolls had significant negative correlation with ASP of the E. vittella larvae.

FUM Gene Expression Profile and Fumonisin Production by Fusarium verticillioides Inoculated in Bt and Non-Bt Maize.

This study aimed to determine the levels of fumonisins produced by Fusarium verticillioides and FUM gene expression on Bt (Bacillus thuringiensis) and non-Bt maize, post harvest, during different periods of incubation. Transgenic hybrids 30F35 YG, 2B710 Hx and their isogenic (30F35 and 2B710) were collected from the field and a subset of 30 samples selected for the experiments. Maize samples were sterilized by gamma radiation at a dose of 20 kGy. Samples were then inoculated with F. verticillioides and analyzed under controlled conditions of temperature and relative humidity for fumonisin B1 and B2 (FB1 and FB2) production and FUM1, FUM3, FUM6, FUM7, FUM8, FUM13, FUM14, FUM15, and FUM19 expression. 2B710 Hx and 30F35 YG kernel samples were virtually intact when compared to the non-Bt hybrids that came from the field. Statistical analysis showed that FB1 production was significantly lower in 30F35 YG and 2B710 Hx than in the 30F35 and 2B710 hybrids (P < 0.05). However, there was no statistical difference for FB2 production (P > 0.05). The kernel injuries observed in the non-Bt samples have possibly facilitated F. verticillioides penetration and promoted FB1 production under controlled conditions. FUM genes were expressed by F. verticillioides in all of the samples. However, there was indication of lower expression of a few FUM genes in the Bt hybrids; and a weak association between FB1 production and the relative expression of some of the FUM genes were observed in the 30F35 YG hybrid.

Tolerance to Stalk and Ear‐Invading Worms and Yield Performance of Bt and Conventional Corn Hybrids

European corn borer (ECB, Ostrinia nubilalis Hübner) and corn earworm (CEW, Helicoverpa zea Boddie) are important yield‐reducing insect pests of field corn (Zea mays L. var. indentata) in the northeastern United States. Transgenic hybrids bioengineered to express insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have revolutionized methods to control these caterpillars and other insect pests in corn. However, corn producers are faced with two decision‐making challenges every year: selection of the most appropriate Bt hybrids for the targeted pest complex from a large list of commercially available hybrids, and finding competitively yielding conventional hybrids for the required refuge hectare. This study was conducted at five sites across Maryland for 3 yr to evaluate more than 100 hybrids representing six Bt trait groups (three single‐protein and three multi‐protein genes) and a conventional non‐Bt group for their relative susceptibility to lepidopteran feeding injury and yield performance. Conventional hybrid tolerance to ECB injury or CEW ear damage and their yield varied each year except Dekalb DKC61‐22, which consistently produced greater yield than other non‐Bt hybrids. Injury caused by ECB was not found among any of the Bt hybrid groups. Hybrids with multi‐protein Bt traits showed greater ear protection than those with single‐protein Bt traits, but this improvement was small. Genuity VT3 Pro and Agrisure Viptera 3111 hybrids had the best ear protection and yield performance among the six tested Bt traits.

Nitrogen and phosphorus nutrition and stoichiometry in the response of maize to various N rates under different rotation systems

Better understanding of plant nutrition and nutrient interactions is of critical importance for developing best management practices in crop production. A three-year study was conducted to examine N and P nutrition and their association in maize as affected by rotation system, N application rate and hybrid maize. Rotation by N treatments were composed of maize–alfalfa (MA), maize–soybean (MS) and continuous maize (MM), fertilized in maize year at 0, 50, 100 and 150 kg N ha−1, respectively. The two maize varieties were glyphosate-resistant (RR) non-Bt (non-Bt) and stacked RR + Bt near-isoline (Bt) hybrids. Our data showed that grain yield, stover, and total aboveground (or shoot) dry matter, N and P uptake (except for stover P) in amounts followed the order MA > MS > MM and were well responsive to N rates. Grain and shoot N and P contents of Bt maize was greater (P < 0.05) than those of non-Bt hybrid in MM. The N:P ratio was positively correlated with N application rates, and was greater in rotational maize than in MM. Both hybrids attained their maximum yields at approximately 201 kg ha−1 of grain N and 255 kg ha−1 of shoot N, corresponding to 36 and 43 kg P ha−1 in grain and shoot. Nitrogen harvest index, P harvest index and nutrient internal efficiency were responsive to N rates but were not different between the hybrids. This study revealed that the critical grain and shoot N content achieving maximum yield appeared to concomitantly result in high P contents.

Non Target Effect of Cry1 Ab and Cry Ab x Cry3 Bb1 Bt Transgenic Maize on Orius insidiosus (Hemiptera: Anthocoridae) Abundance

Non-target effects of Cry1Ab x CP4 EPSPS and Cry1Ab+Cry3Bb1×CP4 EPSPS Bt transgenic new maize hybrids on insidious flower bugs [Orius insidiosus (Say)] was studied in Nebraska (Mead, C lay Center, and Concord) during 2007 and 2008. The Bt effect was compared to CP4 EPSPS maize (isoline), conventional maize, and insecticide applications of permethrin (Pounce® 1.5G) and bifenthrin (Capture® 2EC) to control first and second generations of Ostrinia nubilalis (Hubner), respectively. Yellow sticky cards, visual observations, and destructive samplings were used to evaluate O. insidiosus abundance. The yellow sticky card data in 2007 showed that O. insidiosus abundance was lower on Pounce® 1.5G treated non-Bt isoline maize plots compared to the BT transgenic hybrid s at 60 and 90 days after planting (DAP). From visual observations, numbers of O. insidiosus were lower in Pounce® 1.5G treated plots and no adverse effects of the Bt hybrids was observed. In 2008, no significant differences were found among treatments in the sticky card data, but the O. insidiosus population significantly increased, with increasing DAP, where the lowest and highest numbers were recorded at 30 and 120 DAP, respectively. In the visual observation and destructive samplings, numbers of O. insidiosus were lower at Concord compared to other sites. Results from the visual observation data in 2008 also revealed that O. insidiosus abundance was lower on Pounce® 1.5G treated plots compared to other treatments. This study showed no adverse effects of the new BT transgenic hybrids that included stacked resistance genes on O. insidiosus compared to the non-Bt maize hybrids.

Effectiveness of Bt Maize against Corn Rootworm (Coleoptera: Chrysomelidae) and Species Composition in South Dakota Ten Years Following the Introduction of Transgenic Maize

Corn rootworms, Diabrotica spp. (Coleoptera: Chrysomelidae), are the most economically important pest of maize in the United States. The larvae consume maize roots, contributing to poor nutrient uptake, lodging of the plants, and severe yield loss. Transgenic maize expressing toxins from the bacterium Bacillus thuringiensis (Bt) have been employed to combat the pest. However, corn rootworm resistance to Bt maize has recently been reported and spurred research on the effectiveness of Bt toxins against corn rootworm across the Corn Belt. Thus, our objectives were twofold. First, we quantified the efficacy of Bt maize hybrids against corn rootworm in South Dakota. Second, we surveyed populations of Diabrotica species in areas where Bt maize had been grown since its commercialization in 2003. Maize hybrids expressing Cry3Bb1, Cry34/35Ab1, and mCry3A were evaluated at two locations with previous corn rootworm infestations or in fields that were in continuous maize for three or more consecutive years. We reported damage to maize expressing Cry3Bb1 and mCry3A toxins. We also observed significantly higher numbers of western corn rootworm than northern corn rootworm in our Diabrotica species surveys, suggesting that western corn rootworm are the dominant species in the region. This research has implications for maize production and sustainable corn rootworm management in South Dakota and the Northern Plains, and will advance our knowledge of the incidence of resistance to Bt toxins and long-term impact of Bt hybrids on species diversity of Diabrotica.

Control of Corn Rootworm Larvae with Soil-Applied Insecticides and Bt Hybrids, 2014

We established one trial at the Northwestern Illinois Agricultural Research and Development Center near Monmouth, IL, to evaluate the efficacy of soil-applied insecticides and Bt hybrids to control corn rootworm (CRW) larvae. The experimental design was a RCB with four replications. The plot size for each treatment was 10 ft (four rows) × 40 ft. The previous crop was a trap-crop (late-planted corn and pumpkins). Corn was planted on 7 May using a four-row, vacuum-style planter (SRES, South Hutchinson, KS) at a rate of 36,600 seeds/acre in 30-inch rows at an approximate depth of 1.75 inches. Hybrid information is provided in Table 1. Granular insecticides were applied through modified Noble metering units or through modified SmartBox metering …

Estimation of efficacy functions for products used to manage corn rootworm larval injury

AbstractMaize, Zea mays L., is an economically important crop grown throughout the world. Corn rootworm, Diabrotica spp. (Coleoptera: Chrysomelidae), larvae constitute a significant economic threat to maize production in the United States, where yield losses and management costs associated with corn rootworm species exceed $1 billion annually. Furthermore, the introduction of the western corn rootworm, D. virgifera virgifera LeConte, into maize‐producing regions of Europe has made managing corn rootworm larval injury an international concern. Larvae injure maize plants by feeding on root tissue and are the primary target of management activities. Products commonly used to protect root systems from injury include chemical insecticides (seed or soil applied) and genetically modified maize hybrids expressing toxins derived from Bacillus thuringiensis Berliner (Bt). The confirmation of field‐evolved resistance to various Bt toxins in populations of the western corn rootworm presents a significant management challenge. We performed a meta‐analysis to provide a broad understanding of the relative efficacy of the primary products currently being used to manage corn rootworm larval injury, including insecticidal seed treatments, soil insecticides and Bt hybrids (with and without the addition of soil insecticide). Our analysis is unique in the breadth of locations and years included – we analysed 135 individual trials conducted from 2003 through 2014 at multiple sites in both Illinois and Nebraska. Panel data were produced by pairing the mean node‐injury rating for each treatment of a given trial with the mean node‐injury rating for untreated maize. Linear regression models were developed to estimate the relationship between the potential for corn rootworm larval injury and product performance. For a given level of injury potential, the parameters estimated reveal differences in the degree of root protection offered by the various product categories analysed. Implications for developing long‐term, integrated, and sustainable practices for managing this important pest of maize are discussed.

Bioefficacy of mycopathogensVerticillium lecanii Zimmermen andMetarhizium anisopliae Metchnikoff against sucking pests of Bt cotton

Entomopathogenic fungi Verticillium lecanii Zimmermen and Metarhizium anisopliae Metchnikoff have generated a great deal of interest in recent years because of their potential as bio-control component in integrated pest management of cotton. These two mycopathogens were evaluated against sucking pests of Bt cotton during Kharif 2011 and 2012 at Cotton Improvement Project, Mahatma Phule Krishi Vidyapeeth, Rahuri to find out the scope and potentiality of V.lecanii and M.anisopliae against sucking pests of Bt cotton in intra hirsutum Bt hybrid (RCH-2Bt). Mycopathogens V.lecanii (2 x 10 8 cfu/gm and 2 x 10 12 cfu/g) and M.anisopliae @ 2000 g/hectare were evaluated alone and in combination ( V.lecanii + M.anisopliae ). The observations were recorded on 3,5 and 10 days interval after each spray application. Pooled analysis of two years data revealed that V.lecanii (2 x 10 12 cfu/g) @ 2000 g/hectare + M.anisopliae (2 x 10 12 cfu/g) @ 2000 g/ha in combination was found more effective and significantly superior to its lower dose V.lecanii (2 x 10 8 cfu/g)@ 2000 g/ha + M.anisopliae (2 x 10 8 cfu/g) @2000 g/ha. It wasproved superior over all other treatments in reducing aphids, jassids, thrips and whitefly population, however, it was at par with V.lecanii (2 x 10 12 cfu/g) @ 2000 g/ha. Thus, V.lecanii (2 x 10 12 cfu/g) @ 2000 g/ha was found to be the effective dose against all major sucking pests of cotton. Investigation on evaluation of entomopathogenic fungi against natural enemies of sucking pests in Bt cotton revealed that there was no significant adverse impact of V. lecanii and M. anisopliae on the activity of natural enemies viz ., Chrysoperla and Coccinellids; when compared with the population of natural enemies in control. Sole and combine application of V. lecanii and M.anisopliae at all the evaluated doses were not found toxic to natural enemies.

Effect of fertilizer levels on soil nutrient status at different growth stages and yield of Bt and non-Bt cotton

The Bt cotton is one of the outcome of gene revolution undertaken for production of cotton. Growing Bt cotton is proved as profitable as compare to non-Bt cotton which resulted in increase the area under cultivation of Bt cotton in Maharashtra as well as in India. The field experiment on effect of fertilizer levels on soil nutrient status at different growth stages and yield of Bt and non-Bt cotton was conducted at Cotton Improvement Project, Mahatma Phule Krishi Vidyapeeth, Rahuri during May to September, 2008. The experiment was laid out in Factorial Randomized Block Design with three replications and two main treatments i.e ., hybrid Bt RCH-2 and Non-Bt RCH-2 and nine sub treatments with different fertilizer doses i.e. , F 1 -No recommended doses of fertilizer (RDF), F 2 -50 % RDF, F 3 - 75 % RDF, F 4 -100 % RDF, F 5 -125 % RDF, F 6 -150 %RDF, F 7 -100 % RDF+ 2 %DAP spray, F 8 -100 % RDF + 1 % MgSO 4 and F 9 -100 % RDF + 1 % KNO 3 . The common RDF for Bt as well as non-Bt was 100 N, 50 P 2 O 5 and 50 K 2 O kg ha ?1 . The results revealed that the Non-Bt hybrid at 100 % NPK recorded maximum content of available nitrogen, potassium, magnesium and iron in soil as compared to Bt hybrid but except phosphorus which was more in Bt than non-Bt Non-Bt hybrid recorded maximum soil available nitrogen and potassium content in F 9 (100 % RDF + 1 % KNO 3 ) treatment at boll development stage as compared to Bt hybrid. However, magnesium and iron were maximum in F 8 (100 % RDF + 1 % MgSO 4 ) treatment in non-Bt as compared to Bt hybrid and phosphorus content was maximum in F 7 (100 % RDF + 2 % DAP) treatment in Bt as compared to non-Bt hybrid at boll development stage. The application of 100 % RDF + 1 % MgSO 4 spray recorded highest yield of Bt and non-Bt cotton hybrids.

Effect of fertilizer levels on leaf reddening in Bt and non-Bt cotton

Cotton is one of the most important cash crop in our country. Reddening is the most recent predominant problem in Bt cotton which became issue of debate for ascertaining the causes and remedies for reddening. To ascertain the role of nutrients in leaf reddening, the field experiment on effect of fertilizer levels on reddening in cotton on Vertisol was conducted at Cotton Improvement Project, Mahatma Phule Krishi Vidyapeeth, Rahuri during May to September, 2008. The experiment was laid out in Factorial Randomized Block Design with three replications and two main treatments i.e. , hybrid Bt RCH-2 and Non-Bt RCH-2 and nine sub treatments with different fertilizer doses i.e. , F 1 - No recommended doses of fertilizer (RDF), F 2 -50% RDF, F 3 - 75 %RDF, F 4 - 100 %RDF,F 5 -125 %RDF, F 6 - 150 %RDF,F 7 -100 % RDF + 2%DAPspray, F 8 -100 % RDF + 1% MgSO 4 and F 9 -100 % RDF +1 % KNO 3 . The common RDF for Bt as well as non-Bt was 100 N, 50 P 2 O 5 and 50 K 2 O kg ha ?1 . The results revealed that the incidence of leaf reddening was more in Bt cotton than non-Bt cotton. The minimum intensity of reddening in Bt and non-Bt cotton was observed in 100 % RDF + foliar sprays with 1% KNO 3 / 1% MgSO 4 / 2% DAP. Among the foliar spray 1 % KNO 3 showed minimum reddening of leaves, which suggest that at boll development stage the application of nitrogen and potassium were helpful for controlling the reddening in Bt and non-Bt cotton. However, the application of 100 % RDF + 1 % MgSO 4 spray was found to be the best for highest content of chlorophyll as well as yield of Bt and non-Bt cotton hybrids.

Impact of the Bt Corn Proteins Cry34/35Ab1 and Cry3Bb1, Alone or Pyramided, on Western Corn Rootworm (Coleoptera: Chrysomelidae) Beetle Emergence in the Field.

Western corn rootworm, Diabrotica virgifera virgifera LeConte, is a major pest of corn, Zea mays L. The effect of the Bt proteins Cry34/35Ab1 and Cry3Bb1, alone or pyramided in corn hybrids on D. v. virgifera adult emergence was evaluated in field experiments for 3 yr. Experiments were infested artificially with 2,500 viable D. v. virgifera eggs per row meter of corn. The reduction in beetle emergence compared with non-Bt controls, from Cry34/35Ab1, Cry3Bb1, and the pyramided hybrids ranged from 64.3 to 97.4%, 91.1 to 95.2%, and 98.1 to 99.6%, respectively. The sex ratio of emerged beetles was usually female-biased from the Cry3Bb1 and pyramided treatments, but not from Cry34/35Ab1 treatment alone. Emergence from all Bt hybrids was delayed compared with the control, with the delay longest from the pyramided hybrid. In 2013, three egg infestation levels were tested, with density-dependent mortality observed at 1,250 viable eggs per row meter. The effect of Bt proteins on the emergence timing and sex ratio of D. v. virgifera may impact the suitability of resistance management plans, specifically the effectiveness of the refuge strategy. Susceptible males emerging from refuge might not be synchronized to mate with potentially resistant females emerging later from Bt corn hybrids.

Crop phenology, thermal requirement, yield and fiber properties of cotton (Gossypium hirsutum) genotypes as influenced by different environments

A field experiment was conducted during 2012-2013, and 2013-2014 with two dates of sowing as main plot and six genotypes as sub-plot treatments. Late sowing resulted in significant reduction in the days to 50 % flowering, days to 50 % boll bursting and days to maturity as well as number of GDDs for boll bursting and maturity compared to normal sowing. The fiber quality parameters, viz., 2.5 % span length, uniformity ratio, micronaire value, fiber strength, elongation and fiber maturity exhibited sig- nificant decline under late sowing. However, short fiber index increased under late sowing. Late sown crop could not develop a full canopy surface area as evidenced by reduced plant height, sympodia, leaf area and LAI at dif- ferent growth stages. The Bt hybrid, Ankur-3028 BG-II recorded significantly higher plant height, sympodia, number of bolls, boll weight, seed cotton yield, seed and lint index and fiber properties like 2.5 % span length, fiber strength. The Bt hybrid G.Cot.Hy.-8 BG-II was early in terms of days to 50 % squaring, flowering, boll bursting and maturity and required less GDDs to attain a particular growth stage. The genotype Ankur-3028 BG-II took sig- nificantly higher number of GDDs during flowering to boll opening stage.

Evaluation of soil‐applied insecticides with Bt maize for managing corn rootworm larval injury

AbstractThe western corn rootworm, Diabrotica virgifera virgifera LeConte, is considered one of the most significant insect pests of maize in North America. Larvae of other secondary subterranean pests such as grape colaspis, Colaspis brunnea (F.), and Japanese beetle, Popillia japonica Newman, can also injure maize seedlings and cause yield loss. In the past decade, maize hybrids containing Bt proteins have been used to manage the western corn rootworm; additionally, seeds are commonly treated with a neonicotinoid and fungicide combination to control secondary pests. Recently, soil‐applied insecticides have been used in conjunction with rootworm Bt hybrids (and seed‐applied insecticides) in areas with perceived risk for increased rootworm larval or secondary pest damage. We conducted a series of trials from 2009 to 2011 that examined multiple rootworm Bt hybrids and their near‐isolines, along with two soil‐applied insecticides, to determine whether the Bt plus insecticide combination resulted in an increased level of efficacy or yield. We also sampled for Japanese beetle and grape colaspis larvae to determine their potential for reducing yield. Densities of secondary pests in our trials were low and likely had no effect on maize yield. The addition of a soil‐applied insecticide to rootworm Bt hybrids improved efficacy only once across 17 location‐years, when overall corn rootworm injury was highest; an improvement in yield was never observed. Our results suggest that the use of a soil‐applied insecticide with a rootworm Bt hybrid should only be considered in scenarios with potentially significant rootworm larval populations. However, potential negative consequences related to trait durability when soil insecticides are used with rootworm Bt maize should be considered.

Comparative susceptibility of transgenic Bt cotton hybrids to Earias spp. and other non-target insects

Four Bt cotton (Gossypium hirsutum L.) hybrids, each with one of four different events, viz., MRC 6301 Bt (cry1Ac gene), JKCH 1947 Bt (modified cry1Ac gene), NCEH 6R Bt (fusion cry1Ac/cry1Ab gene) and MRC 7017 Bollgard II (cry1Ac and cry2Ab genes) were evaluated along with their respective isogenic non-Bt genotypes against Earias spp., sucking insect pests, and predators in 2010 and 2011. Female oviposition was not significantly different between Bt and non-Bt cotton hybrids. All Bt cotton hybrids recorded significantly reduced damage of Earias spp. in shoots, squares, green bolls and freshly shed fruiting bodies as compared to the isogenic non-Bt genotypes. In 2010, the incidence of Earias spp. was observed only on 136 day old crop or later. MRC 7017 Bollgard II had the lowest damage followed by NCEH 6R Bt, MRC 6301 Bt and JKCH 1947 Bt. However, no damage was observed in any of the Bt hybrids throughout the cropping season in 2011. The time of first appearance of Earias spp. on Bt cotton differed from non-Bt genotypes, whereas, first appearance of sucking insects and predators did not differ between Bt and their isogenic non-Bt genotypes. Populations of sucking insect pests {Amrasca biguttula biguttula (Ishida), Bemisia tabaci (Gen.) and Thrips tabaci (Lindemann)} varied significantly among different cotton genotypes. Nevertheless, their incidence on Bt cotton hybrids did not differ significantly from the respective isogenic non-Bt genotypes. No significant differences were observed with respect to relative abundance of predators, viz., spiders, chrysopids and coccinellids on Bt and non-Bt cotton genotypes. All Bt cotton hybrids out-yielded their isogenic non-Bt genotypes during both years. The yield was significantly higher in MRC 7017 Bollgard II followed by MRC 6301 Bt, NCEH 6R Bt and JKCH 1947 Bt. The selection of superior genotypes with better yield characteristics is thus vital for developing high yielding transgenic cotton.

Impact of Harvest-aid Defoliants on Yield of American Cotton and Their Monetary Evaluation

Field experiments were conducted during Kharif 2012 and 2013 to determine the effect of two harvest-aid defoliants i.e Dropp ultra® and Ethrel, their application rates and time of application on three American cotton cultivars. Pooled data revealed significantly higher seed cotton yield for Bt hybrids MRC7361BGII (3055.2kg/ha) and MRC7017BGII (2913.0 kg/ha) as compared to non Bt variety F1861 (2346.0 kg/ha). Among tested defoliants, Dropp ultra® @200ml/ha resulted in better SCY, lint and seed yield. This yield enhancement in case of Dropp ultra® @ 200 ml/ha further lead to significantly better net returns (? 85373/ha) and B: C ratio (2.31) over other treatments. Application of defoliants at 150DAS resulted in significantly improved net returns (? 79288/ha) as compared to earlier application (? 73632/ha) at 140 DAS. Improved water productivity and fertilizer use efficiency coupled with better B: C ratio for Dropp ultra® @ 200 ml/ha at 150 DAS clearly indicated its superiority among all treatments. Therefore Bt hybrids seems to be superior over the non Bt varieties and application of ethrel@2000ppm or dropp ultra® @ 200 ml/ha at 150 DAS should be adopted as useful production practice for enhancing cotton yield under semi-arid conditions of north-western India.

Performance of BG-I and BG-II Bt Cotton hybrids againstAphis gossipiandAmrasca bigutulla bigutulla

Among all BG-I Bt cotton hybrids, aphid population ranged from 7.18 to 17.58/three leaves. Minimum aphid population was recorded on ACH-155 (7.18) and maximum on RCH-2 (17.58). Among BG-II cotton hybrids, aphid population ranged from 7.63 to 19.70/three leaves. Minimum aphid population was observed on ACH-155 (7.63) and maximum on MRC-7326 (19.70). Among all Bt cotton (BG-I and BG-II) hybrids, aphid population ranged from 7.18 to 19.70/three leaves. Minimum aphid population was observed on ACH-155 BG-I (7.18) which was found significantly superior over rest of hybrids except SP-499 BG-I (7.29), SP-1037 BG-I (7.30) and ACH-155 BG-II (7.63) which were at par with each others. Maximum population of aphid was observed on MRC-7326 BG-II (19.70) over rest of hybrids except UPLHH-2 BG-II (18.24), RCH-2 BG-II (18.06) and RCH-2 BG-I (17.58) which were at par with each others. The jassid population on BG-I Bt hybrids ranged from 1.50 to 5.64/three leaves, minimum being on ACH-21-1-BG-I (1.50/three leaves) and maximum on RCH-2 BG-I (5.64/three leaves). Among BG-II hybrids it ranged from 1.95 to 6.95/three leaves, minimum being on MRC-7326 BG-II (6.95/three leaves), followed by VBCH-1501 BG-II (6.52/three leaves). Among all Bt cotton hybrids jassid population ranged from 1.50 to 6.95/three leaves.

Performance and behaviour of Bt cotton hybrids under sub-optimal rainfall situation

Growth behaviour and yield performance of Bt cotton hybrids under sub-optimal rainfall situation is of practical significance, because more than 60% of the cotton area is under rainfed condition in India. A field trial conducted in a sandy clay loam soil during the seasons 2006–2007, 2007–2008, and 2008–2009 to study the growth behaviour and yield performance under scanty rainfall situation revealed that growth in both Bt and non-Bt cotton hybrids significantly differed under these parameters. The crop experienced moisture stress at the early stages of growth and again during boll development phase in 2006–2007 and 2008–2009. However, Bt hybrids (1691 kg ha−1) produced higher seed cotton yield than non-Bt hybrids (1092 kg ha−1), while the controlled variety (LRA 5166) performed the average of these two (1399 kg ha−1). Similar trend was evident in respect of bolls per plant (at 90 DAP) and the final harvested bolls in both Bt and non-Bt cotton. Because of Bt gene, the early formed bolls were protected from the boll worms which led to less damage and higher yield with Bt hybrids. Amongst the hybrids, RCHB 708 Bt (1917 kg ha−1) performed better over the others.

Improving the fertilizer use efficiency and profitability of small farms by intercropping with transgenic Bt cotton

Bt transgenic hybrid cotton productivity and profitability could not be sustained after 2007 in India which necessitated to investigate into the nutrient needs of transgenic Bt hybrid cotton and their intercropping systems. Seven Bt transgenic hybrid cotton intercropping systems with four fertilizer management practices and two plant spacings were evaluated in split plot design during 2010-12 in Vertisols at Central institute for Cotton Research, Nagpur, India. Present recommendation of Pigeon pea refugea as stripcropping (2:8) with transgenic Bt hybrid cotton reduced seed cotton yield by 69%, therefore, not accepted by 82% farmers. Tagetus sp. or Dolichus lab lab were advocated as better refugea with economic advantage of US $ 600 ha-1 with C: B ratio of 1:2.8. However, a net a profitability of US $768 and 662 ha-1 with a C:B ratio of 1:3.7 and 1:3 were achieved in intercropping with roselle or soybean compared to US $ 348 C:B ratio of 1:2.5 only with transgenic Bt hybrid cotton alone. This study also breaks the myth of 30% extra fertilizer dose for transgenic Bt hybrid cotton, which requires 90:20:37 N:P:K kgha-1 only and soybean intercropping requires additional 14:13:0 N:P:K kg ha-1. Any deficiencies arising can be economically corrected with two prophylactic foliar sprays of NMgB after square initiation. NPK uptake, nutrient and fertilizer use efficiencies were significantly improved in transgenic Bt hybrid cotton and intercropping with soybean and roselle (except PUE). Hand weeding cost was minimum in soybean and maximum in roselle with Pendimethalin PPI rotated with Pyrithiobac Na EPE. Key words: Transgenic Bt hybrid cotton, fertilizer use efficiency, intercropping, small farms, soybean.