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Résumé

Originating from the tropics, historical maize varieties require a short-day/long-night cycle to undergo reproductive transition. Under long-day conditions, the transition is blocked or severely delayed, a phenomenon referred to as photoperiod sensitivity (PS) that results in late flowering time and poor fitness. Selection on variation in PS enabled the spread of maize into the temperate zone with long-day growing seasons, and temperature has become the primary driver of the crop cycle in temperate varieties. Additionally, plant breeding has dramatically improved yields, but with narrow pools of diversity. Thus, both natural and artificial selection has reshaped the phenotypic space for flowering time regulation and reduced the plasticity of temperate breeds, putatively constraining adaption to future environments.

In the context of global warming, where rising temperatures will hasten flowering times, maize yields are projected to decline. Reintroducing partial PS in temperate breeding pools could counteract these effects and expand the phenotypic space for adapting maize to climate change. However, to exploit the potential of PS for maize adaptedness, the ecophysiological response of flowering time across a daylength gradient has to be better understood.

PS is a physiological trait characterized by a delay in flowering time (measured by extra leaf emission or extra growing degree days) associated with a daylength increase, occurring beyond a threshold of sensitivity distinguishing short- from long-day environments. This response can be parametrized in crop model as a physiologically informed function, which defines a “reaction norm.” In terms of genetic architecture PS is a complex trait, but a few “large-effect” alleles (each extending flowering time by 0.5-3.0 d) have been historical targets of selection. These could be reintroduced to manipulate flowering time of temperate maize.  

In order to investigate the potential for reintroducing PS into temperate maize for adaptation to climate change, the first objective of this thesis will be to generate new knowledge about the physiological reaction norm of flowering time. The PS response will be explored at the genotypic and haplotypic scales, in inbreds and hybrids, using an ecophysiologically designed field network and existing datasets. Separately, the aim is to determine how PS alleles from tropical lines modify the physiological reaction norm of temperate breeding lines, and in turn, how this affects other traits including yield. Ultimately, the variation in physiological reaction norm and the allelic effect of PS on yield related traits will serve to parametrize and validate a crop growth model that could simulate PS response in temperate maize. With this new model, time to flowering and yield will be simulated for varieties with distinct physiological reaction norms across a grid of sites in Europe and the United States (main zones of maize production in temperate latitudes) for past, current, and future climatic scenarios. The relative impact of including photoperiod-regulation on the response to flowering time and yield will be used to assess whether PS is expected to improve maize productivity and/or yield stability today and in the future.

Contact

• Justine Drouault 

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Publications

Nicole E Choquette, James B Holland, Teclemariam Weldekidan, Justine Drouault, Natalia de Leon, et al.. Environment‐specific selection alters flowering‐time plasticity and results in pervasive pleiotropic responses in maize. New Phytologist, 2023, 238, pp.737 - 749. ⟨10.1111/nph.18769⟩. ⟨hal-04040008⟩