Managing resistance evolution to transgenic Bt maize in corn borers in Spain

Post-genomic era in agriculture and veterinary science: successful and proposed application of genetic targeting technologies

Gene editing tools have become an indispensable part of research into the fundamental aspects of cell biology. With a vast body of literature having been generated based on next generation sequencing technologies, keeping track of this ever-growing body of information remains challenging. This necessitates the translation of genomic data into tangible applications. In order to address this objective, the generated Next Generation Sequencing (NGS) data forms the basis for targeted genome editing strategies, employing known enzymes of various cellular machinery, in generating organisms with specifically selected phenotypes. This review focuses primarily on CRISPR/Cas9 technology in the context of its advantages over Zinc finger proteins (ZNF) and Transcription activator-like effector nucleases (TALEN) and meganucleases mutagenesis strategies, for use in agricultural and veterinary applications. This review will describe the application of CRISPR/Cas9 in creating modified organisms with custom-made properties, without the undesired non-targeted effects associated with virus vector vaccines and bioactive molecules produced in bacterial systems. Examples of the successful and unsuccessful applications of this technology to plants, animals and microorganisms are provided, as well as an in-depth look into possible future trends and applications in vaccine development, disease resistance and enhanced phenotypic traits will be discussed.

Monitoring Insect Resistance to Bt Maize in the European Union: Update, Challenges, and Future Prospects

Transgenic maize producing the Cry1Ab toxin of Bacillus thuringiensis (Bt maize) was approved for cultivation in the European Union (EU) in 1998 to control the corn borers Sesamia nonagrioides (Lefèbvre) and Ostrinia nubilalis (Hübner). In the EU since then, Cry1Ab is the only Bt toxin produced by Bt maize and Spain is the only country where Bt maize has been planted every year. In 2021, about 100,000 hectares of Bt maize producing Cry1Ab were cultivated in the EU, with Spain accounting for 96% and Portugal 4% of this area. In both countries, Bt maize represented less than 25% of all maize planted in 2021, with a maximum regional adoption of 64% Bt maize in northeastern Spain. Insect resistance management based on the high-dose/refuge strategy has been implemented in the EU since 1998. This has been accompanied by monitoring to enable early detection of resistance. The monitoring data from laboratory bioassays show no decrease in susceptibility to Cry1Ab had occurred in either pest as of 2021. Also, control failures have not been reported, confirming that Bt maize producing Cry1Ab remains effective against both pests. Conditions in the EU preventing approval of new genetically modified crops, including maize producing two or more Bt toxins targeting corn borers, may limit the future effectiveness of resistance management strategies.

Seven Years of Monitoring Susceptibility to Cry1Ab and Cry1F in Asian Corn Borer

Resistance monitoring in the Asian corn borer, Ostrinia furnacalis, is necessary to accommodate the commercial introduction and stewardship of Bt maize in China. The susceptibility of 56 O. furnacalis field populations, collected between 2015 and 2021 from the corn belt regions of China, to Cry1Ab and Cry1F toxins was determined. Neonate larvae (within 12 h after hatching) were placed on the surface of semi-artificial agar-free diet incorporating a series of concentrations of purified toxins, and mortality was evaluated after 7d. The median lethal concentration (LC₅₀) values of Cry1Ab and Cry1F were 0.05 to 0.37 µg/g (protein/diet) and 0.10 to 1.22 µg/g, respectively. Although interpopulation variation in susceptibility to the toxins was observed, the magnitude of the differences was 5.8-fold and 8.3-fold for Cry1Ab and Cry1F, respectively. These results suggested that the observed susceptibility differences reflect natural geographical variation in response and not variation caused by prior exposure to selection pressures. Therefore, the O. furnacalis populations were apparently still susceptible to Cry1Ab and Cry1F across their range within China. The monitoring data established here will serve as a comparative reference for early warning signs of field-evolved resistance after the cultivation of Bt maize in China.

Effects of Exogenous Salicylic Acid Application to Aboveground Part on the Defense Responses in Bt (Bacillus thuringiensis) and Non-Bt Corn (Zea mays L.) Seedlings

Bt (Bacillus thuringiensis) corn is one of the top three large-scale commercialized anti-insect transgenic crops around the world. In the present study, we tested the Bt protein content, defense chemicals contents, and defense enzyme activities in both the leaves and roots of Bt corn varieties 5422Bt1 and 5422CBCL, as well as their conventional corn 5422 seedlings, with two fully expanded leaves which had been treated with 2.5 mM exogenous salicylic acid (SA) to the aboveground part for 24 h. The result showed that the SA treatment to the aboveground part could significantly increase the polyphenol oxidase activity of conventional corn 5422, the Bt protein content, and peroxidase activities of Bt corn 5422Bt1, as well as the polyphenol oxidase and peroxidase activity of Bt corn 5422CBCL in the leaves. In the roots, the polyphenol oxidase and peroxidase activity of conventional corn 5422, the polyphenol oxidase and superoxide dismutase activities of Bt corn 5422Bt1, the DIMBOA (2,4-dihydroxy-7-methoxy-2H, 1, 4-benzoxazin-3 (4H)-one) content, and four defense enzymes activities of Bt corn 5422CBCL were systematically increased. These findings suggest that the direct effect of SA application to aboveground part on the leaf defense responses in Bt corn 5422CBCL is stronger than that in non-Bt corn. Meanwhile, the systemic effect of SA on the root defense responses in Bt corn 5422CBCL is stronger than that in conventional corn 5422 and Bt corn 5422Bt1. It can be concluded that the Bt gene introduction and endogenous chemical defense responses of corns act synergistically during the SA-induced defense processes to the aboveground part. Different transformation events affected the root defense response when the SA treatment was applied to the aboveground part.

Update of environmental risk assessment conclusions and risk management recommendations of EFSA (2016) on EU teosinte

Teosinte, wild maize relatives originating from Mexico and Central America, emerged as a noxious agricultural weed in France and Spain. In 2016, the European Food Safety Authority (EFSA) issued a technical report that assessed the available scientific information on teosinte for its relevance for the environmental risk assessment (ERA) and risk management (RM) of genetically modified (GM) maize MON810, Bt11, 1507 and GA21 for cultivation. It was concluded that the impact of insect resistance and/or herbicide tolerance in GM teosinte hybrid progeny (potentially acquired through hybridisation between GM maize and teosinte) on target and non-target organisms, the abiotic environment and biogeochemical cycles would be very low under EU conditions. Following a request of the European Commission, EFSA evaluated whether the ERA conclusions and RM recommendations of EFSA (2016) remain applicable, or require revision in light of new scientific evidence on teosinte that has become available since the publication of EFSA (2016). A protocol was developed to clarify the interpretation of the terms of reference of the mandate and make them operational. The assessment relied on evidence retrieved via an extensive literature search and from reports of the Competent Authorities of France and Spain, and on hearing expert testimonies. A limited collection of 18 publications of varying relevance and quality was retrieved and assessed. Based on this evidence, it is concluded that the ERA conclusions and RM recommendations of EFSA (2016) remain applicable, except those pertaining to the use of glyphosate-based herbicides on maize GA21 which should be considered under Regulation (EC) No 1107/2009. In infested agricultural areas (especially in regions where maize MON810 is widely grown), weed management measures implemented to monitor, control and/or eradicate teosinte must remain in place, as they will contribute to further reduce the low vertical gene flow potential between GM maize and EU teosinte.