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Broad adaptive genetic differentiation in forage quality traits but similar phenotypic plasticity in Tunisian populations of Brachypodium hybridum in response to phosphorus deficiency
  • Mohamed Neji,
  • Samir Tlahig,
  • Chedly Abdelly
Mohamed Neji
Borj Cedria Biotechnology Centre

Corresponding Author:mnmedneji@gmail.com

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Samir Tlahig
Institut des RĂ©gions Arides
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Chedly Abdelly
Borj Cedria Biotechnology Centre
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Facing to the harsh environmental constraints, natural populations of widespread plant species may express plastic response, evolve local adaptation or combine both mechanisms in order to maintain their genetic variation and pervasiveness across a wide ecological niche. Here, 79 lines representing height Tunisian populations of Brachypodium hybridum were cultivated in two contrasting phosphorus (P) availability levels and their genetic variation was investigated using forage quality traits to identify the main mechanisms governing their genetic variation. Our results revealed large variation among populations for most traits. PCA analysis showed the separation between coastal and inland populations in both P levels. Importantly, all traits revealed high heritability in both P treatments and the response of most of them to P deficiency was highly influenced by the population effect, which accounted 52.38% of the total variation, indicating strong population differentiation. However, although significant for most traits, only 18.13% of variation was attributed to P treatment, suggesting little plastic response to P deficiency. Importantly, as revealed by the lack of population*treatment effect for most traits, the plastic response was probably common to all populations. Moreover, we found that 56.99% of variation was attributed to environmental factors with distance to coastline, precipitation seasonality, and annual precipitation being the most important factors, suggesting that the strong population differentiation likely reflects local adaptation to specific environmental conditions. Contrary to the coastal populations, which were characterized by high levels of fiber-related traits levels, the inland ones displayed the high values of most energy-related traits, suggesting that these latter were characterized by relatively higher forage quality. Overall, our results suggested that the effect of local adaptation overrides the effect of phenotypic plasticity in explaining the variation of forage quality traits, which indicate a broad adaptive genetic differentiation among the Tunisian populations of B. hybridum in response to P deficiency.