Diversity of Naturalized Hairy Vetch (Vicia villosa Roth) Populations in Central Argentina as a Source of Potential Adaptive Traits for Breeding.

Hairy vetch (Vicia villosa ssp. villosa Roth) is native of Europe and Western Asia and it is the second most cultivated vetch worldwide. Hairy vetch is used as forage species in semiarid environments and as a legume cover crop in sub-humid and humid regions. Being an incompletely domesticated species, hairy vetch can form spontaneous populations in a new environment. These populations might contain novel and adaptive traits valuable for breeding. Niche occupancy based on geographic occurrence and environmental data of naturalized populations in central Argentina showed that these populations were distributed mainly on disturbed areas with coarse soil texture and alkaline-type soils. Low rainfall and warm temperatures during pre- and post-seed dispersal explained the potential distribution under sub-humid and semiarid conditions from Pampa and Espinal ecoregions. Conversely, local adaptation along environmental gradients did not drive the divergence among recently established Argentinian (AR) populations. The highest genetic diversity revealed by microsatellite analysis was observed within accessions (72%) while no clear separation was detected between AR and European (EU) genotypes, although naturalized AR populations showed strong differentiation with the wild EU accessions. Common garden experiments were conducted in 2014-16 in order to evaluate populations' germination, flowering, and biomass traits. European cultivars were characterized by low physical seed dormancy (PY), while naturalized AR accessions showed higher winter biomass production. Detected variation in the quantitative assessment of populations could be useful for selection in breeding for traits that convey favorable functions within specific contexts.

Gene flow in Argentinian sunflowers as revealed by genotyping-by-sequencing data.

Gene flow can have several different applied consequences, ranging from extinction to the escape of transgenes to the evolution of weedy or invasive lineages. Here, we describe patterns of hybridization and gene flow involving domesticated and wild sunflowers in Argentina. To address the risks of introgression of variants from the cultivated sunflower into invasive wild Helianthus, we used genotyping-by-sequencing (GBS) to genotype 182 samples from 11 sites in Argentina, along with previously published data from samples from the native range (North America), to determine the native source populations of the Argentinian samples and to detect admixture. We unexpectedly discovered two distinctive forms of H. petiolaris in Argentina, one from H. petiolaris subsp. petiolaris as expected, but the other from an unknown source. Extensive admixture was observed among Argentinian sunflowers, largely confirming phenotypic predictions. While many hybrids are F1s, there were signals consistent with introgression from the domesticated sunflower into H. petiolaris. Whether this introgression is incidental or a causal driver of invasiveness is not yet clear, but it seems likely that genes found in the domesticated sunflower genome (whether engineered or not) will quickly find their way into wild Argentinian sunflower populations.

AHAS Trp574Leu substitution in Raphanus sativus L.: screening, enzyme activity and fitness cost.

BACKGROUND: Feral radish (Raphanus sativus L.) is a problematic weed that has become resistant to acetohydroxyacid synthase (AHAS) inhibitor herbicides due to the Trp574Leu mutation. An AHAS gene mutation that causes herbicide resistance may have negative pleiotropic effects on plant fitness. This study reports the effects of the Trp574Leu mutation on AHAS activity and reproductive traits of R. sativus. RESULTS: Eight of 17 feral radish accessions presented individuals resistant to metsulfuron-methyl at 0.5% to >90.0% and all the resistant individuals analyzed showed the Trp574Leu mutation. Without herbicide selection, the AHAS activity was 3.2-fold higher in the susceptible accession than in the resistant one. The resistant accession was >9000-fold more resistant to metsulfuron-methyl and imazethapyr than the susceptible accession. Under low intraspecific competition during two growing seasons, AHAS-resistant feral radish accessions showed 22-38% and 21-47% lower seed numbers and yield per plant than the susceptible accession. CONCLUSION: This is the first report of fitness cost associated with the AHAS Trp574Leu mutation in R. sativus populations. This fitness cost could reduce frequency of the resistant allele without herbicide selection. © 2018 Society of Chemical Industry.

Transgene escape and persistence in an agroecosystem: the case of glyphosate-resistant Brassica rapa L. in central Argentina.

Brassica rapa L. is an annual Brassicaceae species cultivated for oil and food production, whose wild form is a weed of crops worldwide. In temperate regions of South America and especially in the Argentine Pampas region, this species is widely distributed. During 2014, wild B. rapa populations that escaped control with glyphosate applications by farmers were found in this area. These plants were characterized by morphology and seed acidic profile, and all the characters agreed with B. rapa description. The dose-response assays showed that the biotypes were highly resistant to glyphosate. It was also shown that they had multiple resistance to AHAS-inhibiting herbicides. The transgenic origin of the glyphosate resistance in B. rapa biotypes was verified by an immunological test which confirmed the presence of the CP4 EPSPS protein and by an event-specific GT73 molecular marker. The persistence of the transgene in nature was confirmed for at least 4 years, in ruderal and agrestal habitats. This finding suggests that glyphosate resistance might come from GM oilseed rape crops illegally cultivated in the country or as a seed contaminant, and it implies gene flow and introgression between feral populations of GM B. napus and wild B. rapa. The persistence and spread of the resistance in agricultural environments was promoted by the high selection pressure imposed by intensive herbicide usage in the prevalent no-till farming systems.

Transgenic glyphosate-resistant oilseed rape (Brassica napus) as an invasive weed in Argentina: detection, characterization, and control alternatives.

The presence of glyphosate-resistant oilseed rape populations in Argentina was detected and characterized. The resistant plants were found as weeds in RR soybeans and other fields. The immunological and molecular analysis showed that the accessions presented the GT73 transgenic event. The origin of this event was uncertain, as the cultivation of transgenic oilseed rape cultivars is prohibited in Argentina. This finding might suggest that glyphosate resistance could come from unauthorized transgenic oilseed rape crops cultivated in the country or as seed contaminants in imported oilseed rape cultivars or other seed imports. Experimentation showed that there are alternative herbicides for controlling resistant Brassica napus populations in various situations and crops. AHAS-inhibiting herbicides (imazethapyr, chlorimuron and diclosulam), glufosinate, 2,4-D, fluroxypyr and saflufenacil proved to be very effective in controlling these plants. Herbicides evaluated in this research were employed by farmers in one of the fields invaded with this biotype and monitoring of this field showed no evidence of its presence in the following years.

Broad resistance to acetohydroxyacid-synthase-inhibiting herbicides in feral radish (Raphanus sativus L.) populations from Argentina.

BACKGROUND: Soon after the commercial release of sunflower cultivars resistant to imidazolinone herbicides, several uncontrolled feral radish (Raphanus sativus L.) populations were found in south-eastern Buenos Aires, Argentina. These populations were studied in field, glasshouse and laboratory experiments aiming to characterise their resistance profile and to develop management tools. RESULTS: Three feral radish accessions were highly resistant to ten active ingredients of five families of acetohydroxyacid synthase (AHAS)-inhibiting herbicides. Sequence analysis of the AHAS gene detected a Trp574Leu mutation in all resistant accessions. One accession with an intermediate level of resistance was heterozygous for this mutation, probably owing to gene exchange with a susceptible subpopulation located in the field margin. Herbicide-resistant and herbicide-susceptible radish could be controlled in sunflower by alternative herbicides. CONCLUSION: This is the first report of feral radish with resistance to herbicides belonging to all the AHAS-inhibiting herbicide families, conferred by Trp574Leu mutation in the AHAS gene. An appropriate herbicide rotation with alternative herbicides such as fluorochloridone or aclonifen and an increase in the diversity of cropping systems are important for minimising the prevalence of these biotypes.