Bacillus thuringiensis-Based Gene Pyramiding: a Way Forward for a Combined Horizontal and Vertical Resistance in Plant

Toxicity of Bacillus thuringiensis Strains to Six Lepidopteran Pests of Brazilian Agricultural Landscape

The first step for biological insecticide production is the evaluating of the pathogenicity and strains virulence of entomopathogens against the target pests. Bacillus thuringiensis (Bt) is widespread in nature, lethal pathogen of a range of orders and the most widely used entomopathogenic biological control agent. Therefore, our objective was to study the susceptibility of six important lepidopteran pests in Brazilian agricultural production systems, Anticarsia gemmatalis (Hübner), Chrysodeixis includens (Walker) Helicoverpa armigera (Hübner), Spodoptera cosmioides (Walker), S. eridania (Cramer), and S. frugiperda (Smith), to Bt strains. In vitro bioassays were conducted with neonate larvae exposed to two Bt strains, 1680A and 775E, in seven concentrations of spores and protein crystals. After 7 days, the mortality was evaluated and indicated that lethal concentration (LC₅₀) for 775E strain ranged from 7.72 × 10⁴ to 2.45 × 10⁶ spores mL^-1 and for 1608A strain from 5.63 × 10³ to 1.21 × 10⁶ spores mL^-1. The strain 1608A was more toxic for A. gemmatalis and H. armigera than 775E strain, and then was further evaluated in greenhouse bioassays with maize and soybean plants infested separately with target insects. The strain 1608A showed an efficient control for most insect species studied in the greenhouse bioassays, promoting considerable reduction in leaf injury and demonstrating a high potential in biological control of important lepidopteran species in crop production systems in Brazil.

Stacking for future: Pyramiding genes to improve drought and salinity tolerance in rice

Abiotic stresses, such as drought and salinity, adversely affect rice production and cause a severe threat to food security. Conventional crop breeding techniques alone are inadequate for achieving drought stress tolerance in crop plants. Using transgenic technology, incremental improvements in tolerance to drought and salinity have been successfully attained via manipulation of gene(s) in several crop species. However, achieving the goal via pyramiding multiple genes from the same or different tolerance mechanisms has received little attention. Pyramiding of multiple genes can be achieved either through breeding, by using marker-assisted selection, or by genetic engineering through molecular stacking co-transformation or re-transformation. Transgene stacking into a single locus has added advantages over breeding or re-transformation since the former assures co-inheritance of genes, contributing to more effective tolerance in transgenic plants for generations. Drought, being a polygenic trait, the potential candidate genes for gene stacking are those contributing to cellular detoxification, osmolyte accumulation, antioxidant machinery, and signaling pathways. Since cellular dehydration is inbuilt in salinity stress, manipulation of these genes results in improving tolerance to salinity along with drought in most of the cases. In this review, attempts have been made to provide a critical assessment of transgenic plants developed through transgene stacking and approaches to achieve the same. Identification and functional validation of more such candidate genes is needed for research programs targeting the gene stacking for developing crop plants with high precision in the shortest possible time to ensure sustainable crop productivity under marginal lands.