RESUMEN

The majority of field corn, Zea mays L., in the southeastern United States has been genetically engineered to express insecticidal toxins produced by the soil bacterium, Bacillus thuringiensis (Bt). Field corn is the most important mid-season host for corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), which has developed resistance to all Cry toxins in Bt corn. From 2020 to 2023, corn earworm pupae were collected from early- and late-planted pyramided hybrids expressing Bt toxins and non-Bt near-isolines in North and South Carolina (16 trials). A total of 5,856 pupae were collected across all trials, with 55 and 88% more pupae collected in later-planted trials relative to early plantings in North and South Carolina, respectively. Only 20 pupae were collected from hybrids expressing Cry1F + Cry1Ab + Vip3A20 across all trials. Averaged across trials, Cry1A.105 + Cry2Ab2 hybrids reduced pupal weight by 6 and 9% in North and South Carolina, respectively, relative to the non-Bt near-isoline. Cry1F + Cry1Ab hybrids reduced pupal weight on average by 3 and 8% in North and South Carolina, respectively, relative to the non-Bt near-isoline. The impact of the Bt toxins on pupal weight varied among trials. When combined with data from 2014 to 2019 from previous studies, a significant decline in the percent reduction in pupal weight over time was found in both states and hybrid families. This study demonstrates a continued decline in the sublethal impacts of Bt toxins on corn earworm, emphasizing the importance of insect resistance management practices.

RESUMEN

The western corn rootworm, (Diabrotica virgifera virgifera LeConte, Coleoptera: Chrysomelidae), is a serious pest of corn (Zea mays Linnaeus, Cyperales: Poaceae) in the midwestern United States. Management practices for corn rootworm larvae include crop rotation, transgenic corn producing insecticidal toxins from the bacterium Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) (Bt), and soil-applied insecticides. The extent to which combining soil-applied insecticide with Bt corn would be beneficial from the perspective of insect resistance management (IRM) or integrated pest management (IPM) remains uncertain. We conducted a 3-yr field study to characterize the implications of combining a soil-applied insecticide and Bt corn for IRM and IPM of western corn rootworm. Experimental treatments were Bt corn, a soil-applied insecticide, the combination of these factors, and an experimental control in which both factors were absent. Data were collected on root injury to corn by rootworm, survival to adulthood, adult size, and emergence time for western corn rootworm. We found that mortality caused by the soil-applied insecticide was insufficient to delay resistance to Bt corn. While combining Bt corn and a soil-applied insecticide may provide a short-term economic benefit, additional research is needed to determine appropriate economic thresholds for combining these tactics. Additionally, combining a soil-applied insecticide and Bt corn would not be sustainable over multiple growing seasons because of its potential to rapidly select for Bt resistance. In general, a more sustainable IRM strategy for rootworm management would include using crop rotation and alternating between non-Bt corn with soil-applied insecticide and Bt corn without soil-applied insecticide.

RESUMEN

Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) has evolved resistance to insecticidal toxins from Bacillus thuringiensis (Bt) Berliner (Bacillales: Bacillaceae) expressed in genetically engineered corn, Zea mays L. This study provides an overview of field trials from Georgia, North Carolina, and South Carolina evaluating Bt and non-Bt corn hybrids from 2009 to 2022 to show changes in susceptibility in H. zea to Bt corn. The reduction in kernel injury relative to a non-Bt hybrid averaged across planting dates generally declined over time for Cry1A.105 + Cry2Ab2 corn. In addition, there was a significant interaction with planting date used as a covariate. The reduction in kernel injury remained above 80% and did not vary with planting date from 2009 to 2014, whereas a significant decline with planting date was found in this reduction from 2015 to 2022. For Cry1Ab + Cry1F corn, the reduction in kernel injury relative to a non-Bt hybrid averaged across planting dates did not vary among years. The reduction in kernel injury significantly declined with planting date from 2012 to 2022. Kernel injury as a proxy for H. zea pressure was greater in late-planted trials in non-Bt corn hybrids. Our study showed that Bt hybrids expressing Cry1A.105 + Cry2Ab2 are now less effective in later planted trials in reducing H. zea injury; however, this was not the case during the earlier years of adoption of corn expressing these 2 toxins when resistance alleles were likely less frequent in H. zea populations. The implications for management of H. zea and for insect resistance management are discussed.

RESUMEN

Protein complexes from edible oyster mushrooms (Pleurotus sp.) composed of pleurotolysin A2 (PlyA2) and pleurotolysin B (PlyB) exert toxicity in feeding tests against Colorado potato beetle (CPB) larvae, acting through the interaction with insect-specific membrane sphingolipid. Here we present a new strategy for crop protection, based on in planta production of PlyA2/PlyB protein complexes, and we exemplify this strategy in construction of transgenic potato plants of cv Désirée. The transgenics in which PlyA2 was directed to the vacuole and PlyB to the endoplasmic reticulum are effectively protected from infestation by CPB larvae without impacting plant performance. These transgenic plants showed a pronounced effect on larval feeding rate, the larvae feeding on transgenic plants being on average five to six folds lighter than larvae feeding on controls. Further, only a fraction (11%-37%) of the larvae that fed on transgenic potato plants completed their life cycle and developed into adult beetles. Moreover, gene expression analysis of CPB larvae exposed to PlyA2/PlyB complexes revealed the response indicative of a general stress status of larvae and no evidence of possibility of developing resistance due to the functional inactivation of PlyA2/PlyB sphingolipid receptors.

Asunto(s)

RESUMEN

Insect resistant genetically modified Bt cotton (containing a gene of Bacillus thuringiensis) has substantial potentiality of mounting cotton productivity. This study unveils an early insight on the economic viability of Bt cotton in Bangladesh. A total of 248 traditional cotton farmers and 8 Bt cotton experimental fields were surveyed in April 2022 for achieving the objectives. The data were analysed using descriptive statistics. Findings showed that the cost of Bt cotton production was slightly higher than that of conventional cotton. However, Bt cotton yielded a productivity increase of 0.81 t/ha. The cultivation of Bt cotton resulted in a higher net return (USD 2436/ha) compared to conventional cotton (USD 1624/ha). The results further indicated that the use of insecticides and pesticides in Bt cotton was significantly lower compared to traditional cotton, thereby contributing to the preservation of the natural environment. Overall, cultivation of Bt cotton is economically viable and may generate environmental benefits. Steps are warranted to disseminate and expand its cultivation.

RESUMEN

Transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) have revolutionized control of some major pests. However, more than 25 cases of field-evolved practical resistance have reduced the efficacy of transgenic crops producing crystalline (Cry) Bt proteins, spurring adoption of alternatives including crops producing the Bt vegetative insecticidal protein Vip3Aa. Although practical resistance to Vip3Aa has not been reported yet, better understanding of the genetic basis of resistance to Vip3Aa is urgently needed to proactively monitor, delay, and counter pest resistance. This is especially important for fall armyworm (Spodoptera frugiperda), which has evolved practical resistance to Cry proteins and is one of the world's most damaging pests. Here, we report the identification of an association between downregulation of the transcription factor gene SfMyb and resistance to Vip3Aa in S. frugiperda. Results from a genome-wide association study, fine-scale mapping, and RNA-Seq identified this gene as a compelling candidate for contributing to the 206-fold resistance to Vip3Aa in a laboratory-selected strain. Experimental reduction of SfMyb expression in a susceptible strain using RNA interference (RNAi) or CRISPR/Cas9 gene editing decreased susceptibility to Vip3Aa, confirming that reduced expression of this gene can cause resistance to Vip3Aa. Relative to the wild-type promoter for SfMyb, the promoter in the resistant strain has deletions and lower activity. Data from yeast one-hybrid assays, genomics, RNA-Seq, RNAi, and proteomics identified genes that are strong candidates for mediating the effects of SfMyb on Vip3Aa resistance. The results reported here may facilitate progress in understanding and managing pest resistance to Vip3Aa.

Asunto(s)

RESUMEN

Cry1A.105 is a bioengineered Bacillus thuringiensis (Bt) insecticidal protein consisting of three domains derived from Cry1Ac, Cry1Ab, and Cry1F. It is one of the two pyramided Bt toxins expressed in the MON 89034 event, a commonly planted Bt maize trait in the Americas. Recent studies have documented that field resistance of the corn earworm, Helicoverpa zea (Boddie), to the Cry1A.105 toxin in maize plants has become widespread in the United States. To investigate the inheritance of resistance to Cry1A.105 in H. zea, two independent tests, each with various genetic crosses among susceptible and Cry1A.105-resistant populations, were performed. The responses of these susceptible, resistant, F1, F2, and backcrossed insect populations to Cry1A.105 were assayed using a diet overlay method. The bioassays showed that the resistance to Cry1A.105 in H. zea was inherited as a single, autosomal, nonrecessive gene. The nonrecessive nature of the resistance could be an important factor contributing to the widespread resistance of maize hybrids containing Cry1A.105 in the United States. The results indicate that resistance management strategies for Bt crops need to be refined to ensure that they are effective in delaying resistance evolution for nonrecessive resistance (nonhigh dose).

RESUMEN

Heterologous expression of exogenous genes, overexpression of endogenous genes, and suppressed expression of undesirable genes are the three strategies of transgenic manipulation for crop improvement. Up to 2020, most (227) of the singular transgenic events (265) of crops approved for commercial release worldwide have been developed by the first strategy. Thirty-eight of them have been transformed by synthetic sequences transcribing antisense or double-stranded RNAs and three by mutated copies for suppressed expression of undesirable genes (the third strategy). By the first and the third strategies, hundreds of transgenic events and thousands of varieties with significant improvement of resistance to herbicides and pesticides, as well as nutritional quality, have been developed and approved for commercial release. Their application has significantly decreased the use of synthetic pesticides and the cost of crop production and increased the yield of crops and the benefits to farmers. However, almost all the events overexpressing endogenous genes remain at the testing stage, except one for fertility restoration and another for pyramiding herbicide tolerance. The novel functions conferred by the heterologously expressing exogenous genes under the control of constitutive promoters are usually absent in the recipient crops themselves or perform in different pathways. However, the endogenous proteins encoded by the overexpressing endogenous genes are regulated in complex networks with functionally redundant and replaceable pathways and are difficult to confer the desirable phenotypes significantly. It is concluded that heterologous expression of exogenous genes and suppressed expression by RNA interference and clustered regularly interspaced short palindromic repeats-cas (CRISPR/Cas) of undesirable genes are superior to the overexpression of endogenous genes for transgenic improvement of crops.

RESUMEN

Plants are subjected to biotic and abiotic stresses regularly, which irreparably harm agricultural production. Eco-friendly and sustainable technology to deal with this challenge is to breed abiotic stress tolerant cultivars. To generate crop plants conferring resistance against stresses, conventional breeding was used in the past, but because of the complex heredity of abiotic stress tolerance traits, such techniques remain insufficient in making greater enhancement. Genome-engineering based on CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats-CRISPR associated protein9) has shown enormous potential in developing climate-resilient cultivars. Likewise, the development of chickpea transgenic lines by knockout of 4CL and REV7 genes exhibits drought tolerance which establishes a foundation for future studies in chickpea. In addition, the CRISPR-Cas9 system can boost yield potential under abiotic stress situations by producing non-transgenic plants having the required characteristics. This review article discusses the validation of gene function based on the CRISPR-Cas9 for the development of abiotic stress-tolerant crop plants, emphasizing the chickpea to open the new ventures of generating abiotic stress-tolerant chickpea varieties.

Asunto(s)

RESUMEN

KEY MESSAGE: Transgenic sugarcane expressing V-ATPase subunit E dsRNA affects growth and survival of Sphenophorus levis. Plants being sessile organisms are constantly confronted with several biotic and abiotic stresses. Sugarcane (Saccharum spp) is a major tropical crop widely cultivated for its sugar and other by-products. In Brazil, sugarcane plantations account for significant production losses due to Sphenophorus levis (sugarcane weevil) infestations. With the existing control measures being less effective, there arises a necessity for advanced strategies. Our bioassay injection experiments with V-ATPase E dsRNA in S. levis larvae showed significant mortality and reduction in transcription levels. Furthermore, we down-regulated the V-ATPase E gene of S. levis in transgenic sugarcane using an RNAi approach. The resultant RNAi transgenic lines exhibited reduction in larval growth and survival, without compromising plant performance under controlled environment. Our results illustrate that RNAi-mediated down-regulation of key genes is a promising approach in imparting resistance to sugarcane weevil.

Asunto(s)

RESUMEN

We characterized the metabolites in grains of transgenic protoporphyrinogen IX oxidase-inhibiting herbicide-resistant rice and weedy accessions using GC-MS and examined whether the chemical composition of their hybrids differed from that of the parents. We found that the metabolite profiles of transgenic rice and weedy rice were clearly separated. Although the metabolite profiles of F2 progeny were partially separated from their parents, zygosity did not affect the profiles. The F2 progeny had similar or intermediate levels of most major nutritional components compared with their parents. However, levels of galactopyranose, trehalose, xylofuranose, mannitol, and benzoic acid were higher in the F2 progeny. Some fatty acids and organic acids also showed prominent quantitative differences between the F2 progeny and the parents. Changes in the metabolite levels of transgenic crop-weed hybrids compared to their parents might influence not only the ecological consequences of the hybrids, but also the nutritional quality and food safety.

Asunto(s)

RESUMEN

Antiviral proteins (AVPs) from plants possess multiple activities, such as N-glycosidase, RNase, DNase enzymatic activity, and induce pathogenesis-related proteins, salicylic acid, superoxide dismutase, peroxidase, and catalase. The N-glycosidase activity releases the adenine residues from sarcin/ricin (S/R) loop of large subunit of ribosomes and interfere the host protein synthesis process and this activity has been attributed for antiviral activity in plant. It has been shown that AVP binds directly to viral genome-linked protein of plant viruses and interfere with protein synthesis of virus. AVPs also possess the RNase and DNase like activity and may be targeting nucleic acid of viruses directly. Recently, the antifungal, antibacterial, and antiinsect properties of AVPs have also been demonstrated. Gene encoding for AVPs has been used for the development of transgenic resistant crops to a broad range of plant pathogens and insect pests. However, the cytotoxicity has been observed in transgenic crops using AVP gene in some cases which can be a limiting factor for its application in agriculture. In this review, we have reviewed various aspects of AVPs particularly their characteristics, possible mode of action and application.

RESUMEN

Transgenic corn expressing insecticidal proteins derived from the bacterium Bacillus thuringiensis (Bt) is an important pest management tool. Western corn rootworm, Diabrotica virgifera virgifera LeConte, is a key pest of corn in the midwestern United States that has developed field-evolved resistance to all available Bt traits. The first Bt trait to be commercialized for management of rootworm was Cry3Bb1 in 2003, and field-evolved resistance appeared in 2009. In this study, we examined fields in counties where greater-than-expected injury to Cry3 (Cry3Bb1 or mCry3A) corn roots (>1 node) had previously been reported (problem counties) and counties where injury had not been reported (non-problem counties). Four to eight fields were sampled per county in 2015, 2016, and 2017 to quantify rootworm abundance, root injury, Cry3Bb1resistance, and rootworm management strategies. Rootworm abundance, root injury, and resistance to Cry3Bb1 did not differ between county types. Management tactics differed between county types, with problem counties growing more corn, using more soil insecticide, and growing more Cry34/35Ab1 corn. Additionally, a comparison of root injury to Bt and non-Bt corn within fields indicated that farmers derived an economic benefit from planting Bt corn to manage corn rootworm. Our results suggest that rootworm populations are similar between problem and non-problem counties in Iowa due to similar levels of selection pressure on Cry3 corn, but problem county fields have applied more management tactics due to previous rootworm issues in the area.

Asunto(s)

RESUMEN

Abiotic stresses negatively influence the survival, biomass production, and yield of crops. Tolerance to diverse abiotic stresses in plants is regulated by multiple genes responding differently to various stress conditions. Genetic engineering approaches have helped develop transgenic crops with improved abiotic stress tolerance including yields. The dehydration-responsive element binding protein (DREB) is a stress-responsive transcription factor that modulates the expression of downstream stress-inducible genes, which confer simultaneous tolerance to multiple stresses. This review focuses on advances in the development of DREB transgenic crops and their characterization under various abiotic stress conditions. It further discusses the mechanistic aspects of abiotic stress tolerance, yield gain, the fate of transgenic plants under controlled and field conditions and future research directions toward commercialization of DREB transgenic crops.

RESUMEN

Controversy continues to exist regarding whether the transgene for glyphosate resistance (GR) and/or glyphosate applied to GR crops adversely affect plant mineral content. Field studies were conducted in 2013 and 2014 in Stoneville, MS and Urbana, IL to examine this issue in maize. At each location, the experiment was conducted in fields with no history of glyphosate application and fields with several years of glyphosate use preceding the study. Neither glyphosate nor the GR transgene affected yield or mineral content of leaves or seed, except for occasional (<5%) significant effects that were inconsistent across minerals, treatments, and environments. Glyphosate and AMPA (aminomethylphosphonic acid), a main degradation product of glyphosate, were found in leaves from treated plants, but little or no glyphosate and no AMPA was found in maize seeds. These results show that the GR transgene and glyphosate application, whether used for a single year or several years, have no deleterious effect on mineral nutrition or yield of GR maize.

Asunto(s)

RESUMEN

The general increase of the cultivation and trade of Bt transgenic plants resistant to Lepidoptera pests raises concerns regarding the conservation of animal and plant biodiversity. Demand for biofuels has increased the cultivation and importation of oilseed rape (Brassica napus L.), including transgenic lines. In environmental risk assessments (ERAs) for its potential future cultivation as well as for food and feed uses, the impact on wild Brassicaeae relatives and on non-target Lepidoptera should be assessed. Here we consider the potential exposure of butterflies as results of possible cultivation or naturalization of spilled seed in Sicily (Italy). Diurnal Lepidoptera, which are pollinators, can be exposed directly to the insecticidal proteins as larvae (mainly of Pieridae) through the host and through the pollen that can deposit on other host plants. Adults can be exposed via pollen and nectar. The flight periods of butterflies were recorded, and they were found to overlap for about 90% of the flowering period of B. napus for the majority of the species. In addition, B. napus has a high potential to hybridise with endemic taxa belonging to the B. oleracea group. This could lead to an exposure of non-target Lepidoptera if introgression of the Bt gene into a wild population happens. A rank of the risk for butterflies and wild relatives of oilseed rape is given. We conclude that, in environmental risk assessments, attention should be paid to plant-insect interaction especially in a biodiversity hotspot such as Sicily.

Asunto(s)

RESUMEN

Transgenic Bacillus thuringensis (Bt) crops are widely deployed to control lepidopterous pests with minimal impact on non-target soil invertebrates. However, most of the results were obtained from field works, the great environmental variation may conceal the small spatial-temporal scaled changes in microhabitats, such as those created near the roots (rhizosphere) or around decomposing residues (detritusphere), which are expected to impact free-living soil organisms more than the bulk soils. The objective of this study was to assess the impact of root and straw residues of transgenic crops on soil, by comparing nematode communities in the rhizosphere (soil microsites only affected by living root), the detritusphere (soil microsites affected by crop aboveground residues) and the rhizosphere-detritusphere interface (soil microsites intensively co-affected by root and residues) of Bt rice and its non-Bt near isoline. Bt rice did not affect nematode abundance and community composition, however, it enhanced the network connections within nematode communities, in both the rhizosphere and detritusphere, indicating the frequency of co-occurring species increased due to the moderate stress of crystal (Cry) as a labile resource of protein or as a moderate pressure of toxic compounds. Furthermore, 60-80% of the correlation between Cry protein (Cry1Ab/Cry1Ac) and nematode genera were positive in the rhizosphere and detritusphere of Bt rice, suggesting that higher Cry protein concentration was associated with the intensive co-occurrence among nematode populations. This finding offers new insights into how the biotic interactions of non-target soil community response to both live and dead parts of transgenic crop, highlighting the moderate stress of Cry protein might affect the community structure and consequent functioning of soil ecosystem based on the elaborately developed knowledge of biotic interactions via ecological network analysis.

Asunto(s)

RESUMEN

Greater than expected injury by western corn rootworm (WCR) (Diabrotica virgifera virgifera LeConte) to Cry3Bb1 expressing maize hybrids (Zea mays L.) has been reported in southwestern Nebraska. Affected areas of some fields are often associated with high pH calcareous soils where maize growth is poor and iron chlorosis is common. As part of a comprehensive study to understand potential causes of unexpected injury, experiments were conducted during 2013 and 2014 to ascertain whether the calcareous soil conditions and associated poor maize growth negatively affect the expression of Cry3Bb1. Quantitative determination of Cry3Bb1 protein expression levels in root tissues was carried out on plants at V5-V6 growth stage using the enzyme-linked immunosorbent assay. Cry3Bb1 and non-Bt near isoline maize hybrids were artificially infested with Cry3Bb1-susceptible WCR eggs to measure survival and efficacy of Cry3Bb1 maize in calcareous and non-calcareous soils. Results showed that there was not a significant difference in expression of Cry3Bb1 protein between plants from calcareous and non-calcareous soils (18.9-21.2 µg/g fresh weight). Western corn rootworm survival was about sevenfold greater from the non-Bt isoline than Cry3Bb1 maize indicating that Cry3Bb1 performed as expected when infested with a Cry3Bb1 susceptible rootworm population. When survival from calcareous and non-calcareous soils was compared, no significant differences were observed in each soil. A significant positive correlation between soil pH and expression of Cry3Bb1 protein in roots was detected from samples collected in 2014 but not in 2013. No such correlation was found between soil pH and survival of WCR. Results suggest that Cry3Bb1 expression levels were sufficient to provide adequate root protection against WCR regardless of soil environment, indicating that lowered Cry3Bb1 expression is not a contributing factor to the greater than expected WCR injury observed in some southwestern Nebraska maize fields.

Asunto(s)

RESUMEN

Species sensitivity distributions (SSDs) have a long history of use within environmental risk assessment to help make informed decisions about the potential risks associated with a variety of environmental stressors. Current risk assessments for transgenic crops conveying insect protection incorporate bioassays conducted on both pest and non-pest insects. As technology developers commercialize new insecticidal traits, SSDs combine the results of these individual studies to construct what may be a better picture of potential environmental risks. While SSDs have been used by technology developers and regulatory agencies to support transgenic crop risk assessments, they are not yet routine in the industry.

Asunto(s)

RESUMEN

The use of Bt transgenic rice (or Bt rice) remains controversial in several countries, including China. Risk assessments are a prerequisite to confirm the safety of Bt rice for ecosystems before a commercial release. This study was conducted to compare the responses of spider assemblages to Bt rice and nontransgenic rice. Two experiments with different locations and times were conducted, and the data were analyzed using standard diversity indices and multivariate community analysis. With both analytical approaches, spider diversity and assemblage composition were not significantly different between Bt and non transgenic rice fields. However, based on principal component analyses, temporal (seasonal) variations occurred in the composition of the spider assemblage. In this study, Bt rice had no detrimental effects on the spider assemblages, although assemblage composition and species abundance varied during the growing season. This study demonstrated an advantage in using community assemblages and repeated sampling to compare fields over a growing season because changes in the assemblages, and more specifically for some species, not always the most dominant, may vary over time. To more accurately assess the changes in composition and structure of spider assemblages through time, particularly for those species that may require a longer period to detect a response, an increase in sampling effort and longer-term experiments might be required.

Asunto(s)