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Description
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Introduction
Cultivar mixtures are increasingly used as a practice to diversify crops, notably for cereals such as wheat. Cereal mixtures typically yield higher than the individual components grown in monoculture, although with notable variability (Borg et al., 2018). This variability stems from plant-plant interactions within mixed stands, resulting in diverse plant phenotypes, a phenomenon known as phenotypic plasticity. This study aims to (i) assess the extent of phenotypic plasticity in yield between monoculture and mixed stands, (ii) determine the key yield components contributing to this plasticity, and (iii) establish connections between such plasticities and variations in functional traits such as plant height and flowering time. -
Materials, methods
A novel experimental approach relying on precision sowing enabled the phenotyping of each cultivar within mixtures at the individual plant level, focusing on above-ground traits throughout the growth cycle. Eight commercial cultivars of Triticum aestivum L. were cultivated both in pure stands and mixed stands in field plots over two consecutive years (2019-2020, 2020-2021), encompassing contrasted climatic conditions. The management strategy included nitrogen fertilization, fungicide application, and weed removal. Two quaternary mixtures were sown, each comprising cultivars with contrasted height or earliness. The spatial layout of cultivars within each mixture was achieved by randomization (Lieng, Richardt and Dodgson, 2012), ensuring that the varietal identity of each plant was known throughout the experiment. -
Results
Compared to the average of cultivars in pure stands, the height mixture strongly underyielded over both years (-29%) while the earliness mixture overyielded the second year (+11%) and underyielded the first year (-8%). The second year, the magnitude of cultivar’s grain weight plasticity, measured as the difference between pure and mixed stands, was significantly and positively associated with their relative yield differences in pure stands (R2=0.51). We found that some cultivars were dominant, i.e. more productive, in mixtures and that dominance rankings were maintained over both years (Figure 1). When grain weight plasticity, measured as the log ratio of pure over mixed stand, was partitioned as the sum of plasticities in each yield component, its strongest contributor was the plasticity in spike number per plant (~56% of the sum), driven by even stronger but opposed plasticities in both tiller emission and regression. For both years, the plasticity in tiller emission was significantly, positively associated with the height differentials between cultivars in mixture (R2=0.43 in 2019-2020 and 0.17 in 2020-2021).
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Figure 1 - Reaction norms of mean grain weight per plant between pure and mixed stands per cultivar for both mixtures in both years. Vertical segments represent confidence intervals at 95%. Letters indicate pairwise differences between cultivars in pure or mixed stands. Line types indicate if plasticity is significant.
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Discussion
The new experimental design enabled to access to the behavior of each individual plant, and hence to assess plant plasticity in pure vs mixed stands. Despite variable cultivar performances in mixture over the two years, some cultivars remained dominant and, unlike common guidelines, dominance was not related to earliness or height at maturity. Our results also highlighted a link between plasticity in tiller emission and height differential in mixture. Both height and tillering dynamics displayed plasticities typical of the shade avoidance syndrome. The early recognition of potential future competitors for resources via a light quality signal is a known example of active plasticity and, as demonstrated here, a major component of genotype strategies in mixtures. The decomposition of plasticities developed in this study open avenues to better study plant-plant interactions in agronomically-realistic conditions. This study also contributed a unique, plant-level data set allowing the calibration of process-based plant models to explore the space of all possible mixtures (Blanc et al., 2021). -
References
Blanc, E. et al. (2021) ‘Functional–Structural Plant Modeling Highlights How Diversity in Leaf Dimensions and Tillering Capability Could Promote the Efficiency of Wheat Cultivar Mixtures’, Frontiers in Plant Science, 12, p. 734056.
Borg, J. et al. (2018) ‘Unfolding the potential of wheat cultivar mixtures: A meta-analysis perspective and identification of knowledge gaps’, Field Crops Research, 221, pp. 298–313.
Lieng, H., Richardt, C. and Dodgson, N.A. (2012) ‘Random Discrete Colour Sampling’. The Eurographics Association.
| Keywords | plant-plant interactions;phenotypic plasticity;tillering;cultivar mixtures;bread wheat |
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