Ecological and genetic factors determining the dispersion of herbicide resistance in Conyza spp. across soybean cropping regions and seasons in brazil and paraguay

• Autor(a) principal: Kalsing, Augusto
• Data de Publicação: 2023
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UNESP
• Texto Completo: http://hdl.handle.net/11449/242818
• topic: Conyza bonariensis; Conyza sumatrensis; código de barra de DNA; sequenciamento de DNA; hibridização; DNA barcoding; DNA sequencing; hybridization

Soybean has been grown in about 45 million hectares in Brazil and Paraguay in 2022. This crop is cultivated across regions that differ by environment and management. Herbicides are one of the main methods to protect soybean yields against weeds. However, over-reliance of herbicides imposed high selection pressure on weeds. Conyza spp. have been exhibited multiple-resistance to herbicides in these countries. Frequency and dispersion of resistance are variable among soybean cropping regions. Thus, the general objective of the study was to access the frequency and dispersion of herbicide-resistant Conyza spp. across regions and seasons in Brazil and Paraguay. Seeds from mature plants that have escaped the control by diverse herbicide programs were sampled from more than 400 preharvest soybean fields in 2019, 2020 and 2021. In the first assay, five DNA barcodes and 32 morphological traits were used to identify the Conyza species associated to soybeans and their dispersion across the regions. After, 2,998 single-nucleotide polymorphisms were found by genotyping by sequencing to investigate the genetic diversity and structure among accessions of Conyza spp. Finally, in the third assay, the frequency and dispersion of Conyza accessions resistant to five synthetic auxins were evaluated using pre-characterized discriminating doses. The combination of its and rps16-trnQ gene regions and reproductive traits supported the taxonomic resolution of C. bonariensis and C. sumatrensis in the sampled fields. Strong genetic structure has separated C. bonariensis from C. sumatrensis and clustered individuals into three genetic groups associated to the cropping regions. However, individuals of C. bonariensis were structured within C. sumatrensis clusters, which indicate interspecific gene flow of resistance alleles between Conyza species. Resistance to 2,4-D was widespread in Brazil, mainly in in the Southern of the country, while resistance to dicamba and triclopyr was significantly less frequent and dispersed. Resistance to auxin herbicides in Conyza spp. is a growing problem in Brazil and must be managed based on strict herbicide rotation and integrated weed management.