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RAPID EVOLUTION OF INVASIVE SUNFLOWER
I try to understand the relative importance of demographic and evolutionary processes on successful naturalization and range expansion of wild sunflower in Argentina, with emphasis on seed dormancy variations.
In a recent study, using chloroplast and nuclear SSR markers, we characterized the invasion history of Argentinean populations, finding evidence of multiple introductions (from historically isolated populations) and post-introduction admixture (Hernández et al. 2019). Just see that the three native genetic clusters are well represented in Argentina and how many haplotypes (founders?) Arg populations have.
That study help us to explain the high phenotypic variation in Argentinean populations observed in earlier studies of the group and warned us about the evolutionary potential of Arg populations.
Germination timing is a key developmental phase which maximize the chances of survival to reproduction in each local environment and it is mainly regulated by seed dormancy. Evaluating seed dormancy of seeds produced in common garden of Native and introduced populations we found that introduced populations have, on average, bigger seeds with lower seed dormancy but high genetic variation exists within native and introduced areas. That variation is mostly explained by climatic variables associated to latitude, at least in North American and Argentinean populations.
Geographic distribution of genetic clusters (big charts) and chloroplast haplotypes (small charts) in North America and Argentina. From Hernández et al. (2019).
Seed germination of native (North America) and introduced populations (Argentina and Australia) is mostly explained by latitude of the local environment. From Hernández, Poverene et al. (2019).
For future studies, I plan taking advantage of herbarium specimens from national museums (collected as early as 1907) and modern sequence technologies to better understand how genetic composition of both extant and extinct Argentinean populations has changed over the time.
CROP-WILD HYBRIDIZATION AND WEEDINESS EVOLUTION
Agricultural weeds are plants well adapted to agricultural environments, characterized by frequent disturbance and high water and nutrient inputs. To colonize these environments, plants may evolve "weedy traits" from standing genetic variation but may also acquire some weedy traits by gene flow with weed and/or cultivated populations.
Wild and cultivated sunflower differ in many traits like branching, head number and size, flowering time, and seed size and dormancy, which segregate when wild and cultivated plants hybridize. In ruderal environments, wild-like traits are favored, leading to low fitness of crop-wild hybrids. However, in agricultural environments, some crop traits (e.g. faster growth, herbicide resistance, and early flowering) can be favored (Presotto et al. 2019).
In a previous study, focused on a natural crop-wild hybrid population adapted to agricultural habitats, we observed that this adaption was not free. Weedy population grow faster than wilds but also show lower tolerance to defoliation and drought stress (Presotto et al. 2017), i.e. the weedy population was intermediate to crop and wild for growth and stress tolerance.
In the lab, we are carrying out experiments to evaluate phenotypic selection over the entire plant life cycle in wild, cultivated and reciprocal crop-wild hybrids to better predict the risk of crop to wild introgression and the subsequent invasion of agricultural habitats.
Wild and cultivated sunflower differ in branching, head size and number, seed size, pericarp anatomy and seed dormancy
TOLERANCE TO EXTREME TEMPERATURES
Using field, growth-chamber and association mapping approaches, I try to identify superior alleles/haplotypes in stressful environments to contribute to the development of climate-resilient cultivars.
During my PhD, I evaluated the impact of extreme heat temperatures (>40°C) at flowering in wild and cultivated sunflower, finding that wild populations outperform cultivars, and invasive populations outperformed native populations and cultivars (Hernández et al. 2018). Interestingly, by performing a biogeographic analysis with wild populations, I observed a clinal variation in heat stress tolerance, where populations from wetter (but surprisingly not from warmer) environments were more tolerant to heat stress.
In one independent study, I performed several experiments in growth chambers to evaluate the impact of extreme temperatures (>50°C and < -2°C) on plant survival. I observed a clear pattern, wilds outperformed cultivated sunflower under freezing stress but cultivars outperformed wild populations under heat stress (Hernández et al. 2020). More studies are needed but it looks like we have wide genetic variation for tolerance to extreme temperatures in the primary gene pool of sunflower.
Currently, I am interested in identifying superior alleles/haplotypes in stressful environments using contrasting sowing dates in the field. For this, I plan to use the sunflower association mapping population, which consists of almost 300 re-sequenced cultivars. Recent experiments using a local mapping populations gave us promising results.
Paper bags used in the field to evaluate heat stress tolerance in wild and cultivated sunflower
Genetic variation for tolerance to heat stress and freezing stress in wild (grey bars) and cultivated (black bars) sunflower
Genetic variation in growth-related traits in a panel of 80 Argentinean commercial lines genotyped with ~14K high quality polimorphic SNPs across three sowing dates. Manhattan plot show association between growth-related traits and markers in the early sowing date
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