Population genomics of Digitaria insularis from soybean areas in Brazil.

BACKGROUND: Digitaria insularis is a weed species that has gained considerable importance in Brazil's soybean production areas that rely on glyphosate-resistant cultivars. Herbicide-resistant weed populations of this species have been reported in many regions in Brazil, first in the south, followed by later reports in the north. We hypothesized that the spread of herbicide-resistant D. insularis is facilitated by movement of agricultural machinery from the southern regions of Brazil. RESULTS: Population genomics revealed a weak or no genetic structure (FST  = [0; 0.16]), moderate expected heterozygosity (HE  = 0.15; 0.44) and low inbreeding (FIS  = [-0.1; 0.1]) in D. insularis populations. Our data supported the hypothesis that herbicide resistance gene flow predominantly occurred in a south-to-north direction based on a migration analysis. We also found evidence of local adaptation of resistant populations in the northern soybean-growing regions of Brazil. CONCLUSION: Evidence in our work suggests that gene flow of glyphosate-resistant D. insularis is associated with movement of agricultural machinery, although local selection pressure seems to play an important role in the evolution of herbicide resistance throughout the country. Our results suggest preventive practices such as equipment sanitation should be implemented to limit the spread of herbicide resistant D. insularis. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Agricultural insect hybridization and implications for pest management.

Biological invasions, the expansion of agricultural frontiers, and climate change favor encounters of divergent lineages of animals and plants, increasing the likelihood of hybridization. However, hybridization of insect species and its consequences for agroecosystems have not received sufficient attention. Gene exchange between distinct and distant genetic pools can improve the survival and reproduction of insect pests, and threaten beneficial insects in disturbed agricultural environments. Hybridization may be the underlying explanation for the recurrent pest outbreaks and control failures in putative hybrid zones, as suspected for bollworm, corn borer, whiteflies, and stink bugs. Reliable predictions of the types of changes that can be expected in pest insect genomes and fitness, and of their impacts on the fate of species and populations remain elusive. Typical steps in pest management, such as insect identification, pest monitoring, and control are likely affected by gene flow and adaptive introgression mediated by hybridization, and we do not have ways to respond to or mitigate the problem. To address the adverse effects of farming intensification and global trade, we must ensure that current integrated pest management programs incorporate up-to-date monitoring and diagnostic tools. The rapid identification of hybrids, quantification of levels of introgression, and in-depth knowledge of what genes have been transferred may help to explain and predict insect population outbreaks and control failures in the future. © 2019 Society of Chemical Industry.