Modifying shade avoidance to suppress competitors

Shade avoidance responses are well known to enhance individual plant fitness at high densities by positioning the photosynthesizing leaves away from the shade caused by neighbor plant leaves. However, in isogenic monocultures, such as most crop fields, all plants are likely showing the exact same responses, thus canceling out the advantage that any individual plant could have from it. In other words, resources have been invested without delivering a selective advantage. In fact, there could even be an additional disadvantage: vertical elongation growth and upward leaf movement will likely lead to a more open canopy structure that would promote light penetration deep inside the canopy down to the soil. This might be good for photosynthesis in lower leaves, but it might be especially beneficial for weeds dwelling in these canopy strata. Agro-ecologists, such as R.F. Denison [1] and J.J. Weiner [2] have proposed theories known as “Darwinian agriculture”[1] or “Evolutionary Agroecology”[2]. They propose that weed suppression by a crop community would not benefit from shade avoidance, but rather would suffer, following the principles of light penetration outlined above. The faster a crop canopy closes, the less likely it is that weeds can proliferate. Canopy closure can for example be optimized by changing planting patterns from the well-known rows to more uniform distributions such as checkerboard designs or hexagonal patterns [2].

The postulation that reduced shade avoidance responses would be beneficial to canopy performance was never tested since dedicated shade avoidance mutants are typically not available in crops. We decided to test this idea in Arabidopsis, using some of the established shade avoidance mutants that are available. Our data are now available online at the biorXive preprint server (, work done primarily by postdoc Chrysa Pantazopoulou. The take home message from our investigations is that reducing hyponastic leaf movement responses in this rosette plant increases canopy closure and inhibits growth of an invading competitor. These findings are indeed consistent with predictions from evolutionary agroecology.

Following a similar line of reasoning, we are now also studying if rice canopy architecture can be optimized to cast more shade on invading weeds to suppress them in a sustainable way. We collaborate with the teams led by Rashmi Sasidharan and Kaisa Kajala at Utrecht University and with the International Rice Research Institute (IRRI). In this study, Martina Huber is investigating genetic variation for shoot architecture in rice, including its responsiveness to density-associated light cues. Justine Toulotte on the other hand is investigating the tolerance of weeds to flooding, which is the classic way of weed suppression in rice paddies. This work is funded by the TTW domain of The Netherlands Organization for Scientific Research (NWO).

[1] Denison RF, 2012. Darwinian Agriculture. pp272, Princeton University Press.

[2] Weiner JJ, 2010. Evolutionary Agroecology: the potential for cooperative, high density, weed-suppressing cereals. Evolutionary Applications. doi:10.1111/j.1752-4571.2010.00144.x

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