Abstract. Feralization is an evolutionary process that can reverse domestication traits, giving rise to invasive or weedy plants. Brassica rapa is an example of extensive diversification, producing multiple domesticated crops, while its non-crop forms persist as weeds in disturbed habitats worldwide. In Argentina, the spread of this weed has increased since 2012, when populations resistant to glyphosate (transgenic) and to acetohydroxyacid synthase (AHAS)-inhibiting herbicides (non-transgenic) were first reported. Despite their spread across more than one million hectares with economic consequences, their origin and genetic diversity remain unknown. This study aims to evaluate the genetic diversity and population structure of Argentinian B. rapa accessions and try to infer the origin of herbicide-resistant populations. We analysed 56 Argentinian accessions and compared them with 568 accessions worldwide using genotyping-by-sequencing. A total of 15 790 SNPs were used to analyse genetic diversity, population structure, and phylogeny. Resistant and susceptible Argentinian accessions formed a genetically homogeneous group distinct from global populations. An exception was a population from southwestern Argentina, which clustered separately. The lowest genetic differentiation was observed with weedy strains from South and North America and with European turnips, suggesting a shared origin and local differentiation. The genetic similarity between resistant and susceptible accessions suggests that herbicide resistance may have emerged via local gene flow from transgenic Brassica napus cultivated informally in Argentina. Overall, our findings improve understanding of the genetic diversity and evolutionary history of this weed and provide a genomic baseline for future management strategies, as well as insights into transgene escape.

Abstract: The pink boll worm now became a menace for sustainable cultivation of Bt cotton in India. Based on the data recorded in unsprayed conditions at 13 different locations of north, central and south cotton growing zone between 2007 and 2023, initiation of green boll damage during later part of the season was observed on Bt cotton genotype during 2009–2014 wherein incidence of PBW already existed on non-Bt genotype. In our research, between 2014 and 2017, the central and southern regions of India experienced a rise in the survival of pink bollworms on Bt cotton surpassing the Economic Threshold Level (ETL) whereas in the north zone PBW incidence started in 2018 at experimental locations. The data validate the initial success of Bt/BG-II cotton in its first ten years (2002–2013) of introduction including pink bollworm, which caused negligible green boll damage (0–1.03%) on Bt/BG-II genotypes, while the incidence on non-Bt genotypes was much higher (2.5–23.01%). Following that, an establishment phase was detected in 2014, confirmed by the equal presence of pink boll worm in BG-II and non-Bt, with minimal infestation differences in BG-II and non-Bt, indicating a larger presence of resistant individuals. Following 2014, the coexistence of PBW in BG-II and non-Bt populations was noted concurrently, with a gradual increase in incidence over ETL beginning in the middle of the season. Farmer’s field surveys reported highest number of locations above ETL during 2017 with a decreasing trend both in central and south zone. In the north, infestations were low until 2021, but increased significantly, reaching their highest point in 2023. The emergence and spread of PBW resistance to Bt cotton, facilitated by off-season survival and carryover, poses a substantial threat to the sustainability of BG-II cotton cultivation in India.

Abstract: Since 2002, transgenic crops that produce Cry1Ac and Cry2Ab toxins have been used in India to control bollworms. From 2002 to 2009, Bt-cotton effectively controlled the pink bollworm (PBW). However, since 2009 numerous studies have reported high survival of PBW on Bt-cotton expressing Cry1Ac and Cry2Ab toxins, indicating reduced susceptibility to Cry toxins expressed in Bt-cotton. In the current study, we attempted to estimate the frequency of resistance alleles to Cry1Ac and Cry2Ab toxins in a field collected population of pink bollworms from Andhra Pradesh. Resistance allele frequency was estimated using an F2 screen methodology for the first time after 17 years of Bt-cotton cultivation. Our study finds that the allele frequency for Cry1Ac is 0.082 and for Cry2Ab is 0.054, with a detection probability of greater than 97%. In our survey conducted in 2018–19 and 2019–20, we also noticed high survival and damage by PBW on Bt-cotton expressing Cry1Ac and Cry2Ab. Our survey report reveals, > 30% flower damage, > 90% green boll damage and > 80% locule damage by PBW on Bt-cotton expressing Cry1Ac and Cry2Ab toxins.

Abstract: Transgenic crops producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) control some important insect pests. However, evolution of resistance by pests reduces the efficacy of Bt crops. Here we review resistance to Bt cotton in the pink bollworm, Pectinophora gossypiella, one of the world’s most damaging pests of cotton. Field outcomes with Bt cotton and pink bollworm during the past quarter century differ markedly among the world’s top three cotton-producing countries: practical resistance in India, sustained susceptibility in China, and eradication of this invasive lepidopteran pest from the United States achieved with Bt cotton and other tactics. We compared the molecular genetic basis of pink bollworm resistance between lab-selected strains from the U.S. and China and field-selected populations from India for two Bt proteins (Cry1Ac and Cry2Ab) produced in widely adopted Bt cotton. Both lab- and field-selected resistance are associated with mutations affecting the cadherin protein PgCad1 for Cry1Ac and the ATP-binding cassette transporter protein PgABCA2 for Cry2Ab. The results imply lab selection is useful for identifying genes important in field-evolved resistance to Bt crops, but not necessarily the specific mutations in those genes. The results also suggest that differences in management practices, rather than genetic constraints, caused the strikingly different outcomes among countries.