Cultivation Of Bt Cotton Research Articles

Insect resistance management facing African smallholder farmers under climate change.

Changes in climatic conditions affect pest populations and ultimately result in increased pest status and yield losses. While pesticide application is usually the first defensive tool used to control pest species that threaten crop production, genetically modified (GM) crops with insecticidal traits (Bt crops) are becoming more common. The indiscriminate and over use of insecticides, and absence of insect resistance management (IRM) strategies ultimately lead to evolution of resistance against these technologies. IRM faces significant challenges in the African context. In this paper we use examples of cotton, maize, cowpea and tomato pests to illustrate their potential to evolve resistance to insecticides and also highlight the importance of IRM strategies, both with regard to the use of pesticides and the cultivation of Bt cotton, Bt maize and Bt cowpea.

Frequency of resistance alleles to Cry1Ac toxin from cotton bollworm, Helicoverpa armigera (Hübner) collected from Bt-cotton growing areas of Telangana state of India

Transgenic cotton expressing Bacillus thuringiensis (Bt) cry1Ac and cry2Ab toxin genes is widely cultivated to manage bollworm complex in India. Cotton bollworm Helicoverpa armigera (Hübner) is one of the most serious of this complex. It is likely to evolve resistance to Cry toxins in view of continual selection pressure due to extensive cultivation of Bt cotton. Monitoring susceptibility of cotton bollworm using conventional bioassays is reported to have shown its increasing tolerance to Cry1Ac over the years. We report using an F2 screen Cry1Ac resistance allele frequencies of 0.050 (95% CI 0.022–0.076) and 0.056 (95% CI 0.035–0.075) in the insect populations collected from pigeon pea grown alongside Bt cotton in the respective years of 2016 and 2017 in the Telangana state of India. Compared to our earlier studies for 2013 and 2014, resistance allele frequency to Cry1Ac in the cotton bollworm in the following two years remains unchanged. The significance of these results is discussed in the context of non-Bt host crops acting as refuge for cotton bollworm for ensuring sustainable resistance management.

A study of technological gap in cultivation of Bt-cotton under FLD through KVK Khargone (M.P.)

A study of technological gap in cultivation of Bt-cotton under FLD through KVK Khargone (M.P.)

The mirid bug Apolygus lucorum deploys a glutathione peroxidase as a candidate effector to enhance plant susceptibility.

The mirid bug Apolygus lucorum has become a major agricultural pest since the large-scale cultivation of Bt-cotton. It was assumed that A. lucorum, similarly to other phloem sap insects, could secrete saliva that contains effector proteins into plant interfaces to perturb host cellular processes during feeding. However, the secreted effectors of A. lucorum are still uncharacterized and unstudied. In this study, 1878 putative secreted proteins were identified from the transcriptome of A. lucorum, which either had homology with published aphid effectors or shared common features with plant pathogens and insect effectors. One hundred and seventy-two candidate effectors were used for cell death-inducing/suppressing assays, and a putative salivary gland effector, Apolygus lucorum cell death inhibitor 6 (Al6), was characterized. The mRNAs of Al6 were enriched at feeding stages (nymph and adult) and, in particular, in salivary glands. Moreover, we revealed that the secreted Al6 encoded an active glutathione peroxidase that reduced reactive oxygen species (ROS) accumulation induced by INF1 or Flg22. Expression of the Al6 gene in planta altered insect feeding behavior and promoted plant pathogen infections. Inhibition of cell death and enhanced plant susceptibility to insect and pathogens are dependent on glutathione peroxidase activity of Al6. Thus, this study shows that a candidate salivary gland effector, Al6, functions as a glutathione peroxidase and suppresses ROS induced by pathogen-associated molecular pattern to inhibit pattern-triggered immunity (PTI)-induced cell death. The identification and molecular mechanism analysis of the Al6 candidate effector in A. lucorum will provide new insight into the molecular mechanisms of insect-plant interactions.

Influence of Cry1Ac Toxin From Bt Cotton on the Soil Microbiota

The first record of transgenic cotton cultivation in Brazil was in 2005, of that of the cultivar MON 531, possessing the cry1Ac gene. Since then, no evaluation has been performed to understand whether the cultivation of Bt cotton has caused any interference with the soil microbiota, including bacteria. In this context, our research was aimed to assess whether the cultivation of Bt cotton negatively affects the community of soil bacteria, through quantitative and metagenomic analyses (marker gene 16S rRNA) for phylum identification. Samples of bacterial populations obtained from the soil cultivated with Bt cotton expressing the Cry1Ac toxin were compared with soil samples from the area cultivated with conventional cotton. Significant differences were not observed in the measure of colony-forming units of bacteria between the soils cultivated with Bt and non-Bt cotton; however, differences were detected only when comparing samples from different collection times of the Bt treatment. Cultivation of Bt cotton did not affect the diversity of the soil bacterial population. Overall, our study shows that, similar to most of the works that have been reported worldwide, cultivation of transgenic cotton does not seem to affect the quantity and diversity of natural soil bacteria.

Resistance status of Helicoverpa armigera against Bt cotton in Pakistan

Transgenic cotton expressing the toxin Cry1Ac from Bacillus thuringiensis L. (Bt) is widely cultivated in Pakistan after its formal approval in 2010. The exposure of the local target pests to the Cry1Ac endotoxin for this duration might have changed the baseline susceptibility. To probe the status of resistance in one of the main target pests, Helicoverpa armigera, field-collected larvae were reared in the lab for conducting leaf fed bioassays. Twenty-six cotton accessions collected from farmers, including 25 Bt-cotton and one non-Bt, were tested to quantify the level of Cry1Ac, an insecticidal crystalline protein (ICP), in leaves of lower, middle and upper canopies of plants. The concentration of ICP was tested through Enzyme-linked Immunosorbent Assay and found significantly variable (P < 0.01) between and within accessions. The highest mean expression was observed in Accession-2 and Accession-4, while the lowest in Accession-21 and Accession-19. Among fresh leaf tissues from different parts of the plant, the highest mean expression was recorded at 60days after sowing in upper canopy leaves of cotton accessions, which decreased in lower parts of the plant with the lowest mean expression in lower canopy leaves. Laboratory bioassays, to calculate lethal dose, for H. armigera showed that LD50 and LD95 were 0.62μg/g and 1.59μg/g of fresh tissue weight, respectively. A strong positive correlation also exists between the levels of Cry1Ac protein and insect mortality (r = 0.84). These findings suggested the future risk of cultivation of Bt cotton, carrying single Cry1Ac gene, in Pakistan, as resistance surging in H. armigera against Cry protein. These results may also have significant implications for the resistance management in Bt crops, especially cotton, in future.

Resource Use Efficiency of Bt Cotton in Hanumangarh District of Rajasthan

An attempt has been made to examine the resource use efficiency of Bt cotton in Hanumangarh district of Rajasthan. The purposive random sampling method was used to select 60 farmers. Survey method was adopted to conduct the inquiry by personal interview with the help of interview schedule. The Cobb-Douglas production function was used for estimation of the resources use efficiency. The results revealed that the Marginal Value Product (MVP) to Marginal Factor Cost (MFC) ratio for human labour (1.44), machine labour (5.07), seed (12.76) and irrigation (1.88) were found to be underutilized, which implies the increased usage of these inputs add to the gross income from cultivation of Bt cotton. Hence, there is an ample potential of raising Bt cotton production through adoption of improved and new technologies and optimum utilization of resources like human labour, machine labour, seed, manure and fertilizer, plant protection chemical (PPC) and irrigation with better management practices.

Impact of transgenic Cry1Ac + CpTI cotton on diversity and dynamics of rhizosphere bacterial community of different root environments

The objective of this study was to characterize the diversity and dynamics of rhizosphere bacterial community, especially the response of dominant and rare bacterial taxa to the cultivation of Bt cotton for different root environments at different growth stages. qPCR analyses indicated that bacterial abundances of the taproots and lateral root rhizospheres of the Bt cotton SGK321 were significantly different at seedling and bolling stages. But no significant differences were detected between the same root zones from Bt and the conventional cotton varieties. Total bacterial genera had similar pattern with dominant genera in abundance, and with rare genera in richness to the changes of bacterial community, respectively. Although the rhizosphere bacterial diversity of the three cotton varieties changed in taproot and lateral root, no significant differences were detected in the same root environments between Bt and conventional cotton. Moreover, Soil pH was more correlated with variations in the bacterial community composition than Bt proteins. In conclusion, these results revealed no indication that rhizosphere bacterial community of Bt cotton had different response to increased Bt protein regarding the same root environment. In particular, dominant and rare bacterial taxa showed the variation in diversity and community composition in different root microhabitats.

Transgenic Bt cotton expressing Cry1Ac/Cry2Ab or Cry1Ac/EPSPS does not affect the plant bug Adelphocoris suturalis or the pollinating beetle Haptoncus luteolus.

The widespread cultivation of transgenic Bt cotton makes assessing the potential effects of this recombinant crop on non-target organisms a priority. However, the effect of Bt cotton on many insects is currently virtually unknown. The plant bug Adelphocoris suturalis is now a major pest of cotton in southern China and the beetle Haptoncus luteolus is one of the most ancient cotton pollinators. We conducted laboratory experiments to evaluate the toxicity of the Bt cotton varieties ZMSJ, which expresses the toxins Cry1Ac and Cry2Ab, and ZMKCKC, which expresses Cry1Ac and EPSPS, on adult A.suturalis and H.luteolus. No significant increase in the mortality of either species was detected after feeding on Bt cotton leaves or pollen for 7 days. Trace amounts of Cry1Ac and Cry2Ab proteins could be detected in both species but invitro binding experiments found no evidence of Cry1Ac and Cry2Ab binding proteins. These results demonstrate that feeding on the leaves or pollen of these two Bt cotton varieties has no toxic effects on adult A.suturalis or H.luteolus.

Persistence of Cry1Ac Protein from Transgenic Bt Cotton Cultivation and Residue Returning in Fields and Its Effect on Functional Diversity of Soil Microbial Communities

The persistence of Cry1Ac protein in the soil and its effect on soil microbial communities are a core issue in assessing the ecological risk of transgenic Bacillus thuringiensis (Bt) cotton. In this study a field experiment was conducted on the cultivation of transgenic Bt cotton (Jin 26 and BtJi 668) with the immediate returning of residues to the fields, in order to quantify the Cry1Ac protein content in the fields and investigate its effects on the functional diversity of soil microbial communities. Cry1Ac protein in the residue-soil mixture was gradually degraded in the transgenic Bt cotton fields. After transgenic Bt cotton straw was returned to the fields for 30 d, 63.73% and 58.33% of the initial amounts of Cry1Ac protein were degraded in the Jin 26 and BtJi 668 fields, respectively. Before the crops were sown in the following year (180 d after returning the straw), no Cry1Ac protein was detected in the fields. After returning the cotton straw to the fields for 30 d, the Shannon-Wiener and McIntosh indices of soil microbial communities in the transgenic Bt cotton fields were significantly higher than those in the non-transgenic cotton fields. Meanwhile, the utilization of carbon sources including amino acids, amines, and carbohydrates by the soil microbial communities significantly increased. Both the McIntosh index and the utilization of carbohydrates increased until 180 d. Principal component analysis revealed that amino acids, amides, and carbohydrates were the main carbon sources distinguishing the two principal component factors. These findings indicated that Cry1Ac protein did not accumulate in the fields after transgenic Bt cotton was planted for one year and the residues were immediately returned to the fields; however, the original functional diversity of soil microbial communities was affected continuously.

Transfer of Cry1Ac and Cry2Ab proteins from genetically engineered Bt cotton to herbivores and predators.

With the cultivation of Bt cotton, the produced insecticidal Cry proteins are ingested by herbivores and potentially transferred along the food chain to natural enemies, such as predators. In laboratory experiments with Bollgard II cotton, concentrations of Cry1Ac and Cry2Ab were measured in Lepidoptera larvae (Spodoptera littoralis, Heliothis virescens), plant bugs (Euschistus heros), aphids (Aphis gossypii), whiteflies (Bemisia tabaci), thrips (Thrips tabaci, Frankliniella occidentalis), and spider mites (Tetranychus urticae). Tritrophic experiments were conducted with caterpillars of S. littoralis as prey and larvae of ladybird beetles (Harmonia axyridis, Adalia bipunctata) and lacewings (Chrysoperla carnea) as predators. Immunological measurements (ELISA) indicated that herbivores feeding on Bt cotton contained 5%-50% of the Bt protein concentrations in leaves except whiteflies and aphids, which contained no or only traces of Bt protein, and spider mites, which contained 7 times more Cry1Ac than leaves. Similarly, predators contained 1%-30% of the Cry protein concentration in prey. For the nontarget risk assessment, this indicates that Bt protein concentrations decrease considerably from one trophic level to the next in the food web, except for spider mites that contain Bt protein concentrations higher than those measured in the leaves. Exposure of phloem sucking hemipterans is negligible.

Management practices to control premature senescence in Bt cotton

ABSTRACTCommercial cultivation of Bt cotton produced higher boll load which led to stiff inter-original competition for photosynthates, resulting in early cessation of growth (premature senescence) due to more availability of sink and less sources. To overcome this problem, field experiment was conducted during 2011 and 2012 using five treatments of plant growth manipulation viz. no fruiting branch removal (F1), removal of first fruiting branch (F2), removal of first and second fruiting branch (F3), removal of all squares from first fruiting branch (F4), removal of all squares from first and second fruiting branches (F5), and three potassium (K) application rates viz. 50 kg ha−1 (K1), 100 kg ha−1 (K2), and 150 kg ha−1 (K3). More nodes above white flower were recorded in F5, followed by F3, while minimum were recorded in F1. Among potassium levels, maximum nodes above white flower were recorded in K3 followed by K2 and K1 during both years of study. Plant height recorded at physiological cutout stage or at maturity stage showed that plants gained more height with removal of all squares from first tosecond fruiting branches with higher potassium dose. Leaf K increased with increasing applied potassium and also with square/branch removal. So early removal of squares/fruiting branches along with higher potassium dose helped in delaying canopy senescence in Bt cotton.

Impact of Bt-cotton on soil microbiological and biochemical attributes

Transgenic Bt-cotton produces Bt-toxins (Cry proteins) which may accumulate and persist in soil due to their binding ability on soil components. In the present study, the potential impacts of Bt- and non-Bt genotypes of cotton on soil microbial activity, substrate use efficiency, viable microbial population counts, and nutrient dynamics were studied. Two transgenic Bt-cotton genotypes (CIM-602 CIM-599) expressing cry1 Ac gene and two non-Bt cotton genotypes (CIM-573 and CIM-591) were used to evaluate their impact on biological and chemical properties of soil across the four locations in Punjab. Field trials were conducted at four locations (Central Cotton Research Institute-Multan, Naseer Pur, Kot Lal Shah, and Cotton Research Station-Bahawalpur) of different agro-ecological zones of Punjab. Rhizosphere soil samples were collected by following standard procedure from these selected locations. Results reveled that Bt-cotton had no adverse effect on microbial population (viable counts) and enzymatic activity of rhizosphere soil. Bacterial population was more in Bt-cotton rhizosphere than that of non-Bt cotton rhizosphere at all locations. Phosphatase, dehydrogenase, and oxidative metabolism of rhizosphere soil were more in Bt-cotton genotypes compared with non-Bt cotton genotypes. Cation exchange capacity, total nitrogen, extractable phosphorous, extractable potassium, active carbon, Fe and Zn contents were higher in rhizosphere of Bt-cotton genotypes compared with non-Bt cotton genotypes. It can be concluded from present study that the cultivation of Bt-cotton expressing cry1 Ac had apparently no negative effect on metabolic, microbiological activities, and nutrient dynamics of soils. Further work is needed to investigate the potential impacts of Bt-cotton on ecology of soil-dwelling insects and invertebrates before its recommendation for extensive cultivation.

English

The impact of 9 months cultivation of transgenic Bacillus thuringiensis (Bt) cotton on selected culturable bacterial and fungal populations in rhizosphere soil was investigated. The transgenic Bt cotton line (06Z604M), isoline (99M03) and a non-Bt cotton line (HART 89M) were planted in confined field site in Samuru-Thika where non-Bt cotton had been continuously cultivated for the past 2 years. Rhizosphere soil samples were collected at planting, maturity, flower and boll, and boll-opening stages and harvesting stages of cotton. Numbers of culturable soil microbial groups (bacteria, actinomycetes and fungi) involved in decomposition and nutrients recycling were measured at CFU and population levels. The proteins did not show effects on bacterial, actinomycetes and fungal counts and populations possibly as a result of adsorption of the proteins on soil particles, which could have rendered the proteins inaccessible for microbial utilization. Culturable microbial population and colony counts arranged in decreasing order were 06Z604D>99M03>HART89M, similar to the amounts of MBC and clay in the soils. Moreover, bacteria and fungi counts were higher at 110 DAS in 06Z604D than in 99M03 and HART89M plot soils. Our observations suggest that insecticidal proteins (Cry1Ac and Cry2Ab2) produced by Bollgard II Bt cotton could persist in tropical soils as a result of adsorption on soil clays but that there were no observable effect on the studied culturable microbial groups.The data presented here showed no consistent statistically significant differences (p 0.001) with soil respiration and microbial biomass, which exhibited uneven trend with the treatments. Generally Soil from 06Z604D showed the slight higher microbial populations and CFU count, whilst HART 89M showed slight lower microbial count. This depicts the fact that slight variability in the treatments, quality and content of the root exudates might have a temporal or permanent shift in micro biota populations of a variety of crop studied.This study therefore suggests that a single-year cultivation of transgenic Bt cotton may not affect the functional bacterial and fungi populations in rhizosphere soil. Key words: Bacillus thuringiensis, bacteria, population, colony forming units, fungi, Bt cotton.

Cost, returns and profitability of Bt-cotton production in beed district

Investigation was carried out during the year 2013-14. About 96 Bt-cotton growers were randomly selected from twelve villages of two tehsils of beed district of Maharashtra. Cross sectional data were collected from Bt-cotton grower with the help of pretested schedule by personal interview method. The techniques like mean, percentage, ratio and cost concept of Cost- A, Cost-B and Cost-C were used to analyze the data. The results revealed that per hectare cost of cultivation of Bt-cotton was Rs. 67137.76. Among individual items of expenditure, the share of rental value of land was 31.85 per cent followed by hired human labour (13.79 %), bullock labour (9.21), irrigation (8.17%), seed (7.51%), fertilizers (6.19%), family human labour (5.64 %), manure (5.45%), plant protection (3.75%), machine labour (2.15 %), respectively. Per hectare gross returns and net profit was Rs. 129111.85 and Rs. 61974.09, respectively. Output-input ratio was 1.92.

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.

Supply response of Bt cotton in Haveri district, Karnataka (India) -A profit function approach

Increasing cost of plant protection measures was rendering the cotton cultivation uneconomical in many cotton growing areas. Notwithstanding the debate, the cultivation of Bt cotton is able to offer some respite to many cotton growers in the country. However, the supply response of cotton to several other factors is yet to be ascertained fully to draw meaningful inferences. Hence, the present study was taken up during 2012-13 in Haveri district of Karnataka state to know the supply elasticity of Bt cotton and demand elasticity of inputs used in its cultivation using profit function approach. A total of 80 Bt cotton growing farmers was selected randomly from 8 villages. The major findings revealed that the elasticity of supply of Bt cotton was significant, suggesting that the supply of Bt cotton was sensitive to change in price. The farmers in Haveri district cultivating Bt cotton were highly responsive to changes in cotton price and any fall in the market price of cotton would lead to the replacement of Bt cotton by other competing crops. Hence, cotton prices need to be stabilized. Demand for labour in cotton cultivation is highly elastic; hence there is a need for mechanization in cotton cultivation.

Identification of female sex pheromone of a plant bug, Adelphocoris fasciaticollis Reuter (Hemiptera: Miridae)

AbstractThe plant bug, Adelphocoris fasciaticollis, has begun to resurge and become a key pest for cotton and alfalfa in northern China, along with the widespread cultivation of Bt cotton. To control this plant bug without pesticides, we attempted to develop a new approach by utilizing sex pheromone. The sex pheromone components from the whole‐body extracts were analysed by GC‐MS and gas chromatography–electroantennogram detector analysis (GC‐EAD). (E)‐4‐Oxo‐2‐hexenal and hexyl butyrate, identified as the major components in the extracts of female bugs, elicited strong EAD responses. Field tests indicated that either (E)‐4‐oxo‐2‐hexenal or hexyl butyrate attracted few A. fasciaticollis males and was significantly less active than virgin females and the binary blend. Their ratio was optimized to be 1 : 11. Our results could expand acknowledge of the pheromone of mirids and provide novel approaches to monitor and control this plant bug without pesticides.

Assessment of density-dependent feeding damage by the cotton dusky bug, Oxycarenus laetus Kirby (Hemiptera: Lygaeidae), in cotton

The dusky cotton bug, Oxycarenus laetus Kirby (Hemiptera: Lygaeidae), is a serious threat to cotton due to early cultivation of Bt cotton. These studies were carried out under laboratory and field conditions to estimate the feeding damage caused by O. laetus to seed weight, seed germination, and lint quality of cotton cultivar Bt-121 at 6 bug densities (0, 5, 10, 15, 20, and 25 adult pairs). The results revealed that seed germination and seed weight decreased, whereas percent reduction in seed germination and seed weight over control increased with increasing bug density. Bug density in the range of 5-25 pairs caused approximately 9.3%-40.7% reduction in seed germination and 7.5%-29.5% reduction in 100-seed weight over control in both laboratory and field trails. The color of lint changed from pure-white to white when bolls were exposed to 10 and 15 pairs of bugs, while it changed to light-yellow and slightly yellow when bolls were exposed to 20 and 25 pairs of bugs, respectively. Bug density had a high negative correlation with percent seed germination and 100-seed weight, while it had a high positive correlation with reduction in seed germination, reduction in 100-seed weight, and lint quality, under both laboratory and field conditions. Bug density explained more than 95% of total variability in seed germination, reduction in seed germination, 100-seed weight, and reduction in 100-seed weight under both laboratory and field conditions; it explained less than 95% (93.2%) of total variability in lint staining under field conditions. These results indicate that reductions in seed weight, seed germination, and lint quality depend upon bug density. Hence, appropriate control measures should be adopted to check consistent increases in the dusky cotton bug population to avoid seed germination and lint quality losses.

Impact of transgenic cottons expressing cry1Ac on soil biological attributes

Three transgenic Bt cotton hybrids (RCH-2 Bt, Bunny Bt and NHH 44 Bt) expressing cry1Ac gene were evaluated for their effects on soil biological, microbiological and diversity attributes at 0&amp;ndash;15 cm and 15&amp;ndash;30 cm soil depth under field conditions. At both soil depths, soil respiration rate and fluorescein diacetate hydrolysis were the highest in the soil under Bt cotton grown followed by non-Bt soil, and by the control bulk soil, indicating no adverse effects of Bt cotton on soil microbial activity. Urease and dehydrogenase activities, reflecting potentially available N and the oxidative metabolism in soil, respectively, also increased in the sequence no-crop variant &amp;lt; non-Bt soil &amp;lt; soil under Bt cotton at both soil depths. A similar trend was found with the soil microbial biomass carbon, microbial population and microbial diversity indices. These results suggest that cultivation of Bt cotton expressing cry1Ac gene may not pose ecological or environmental risk.