Understanding the growth-defense trade-off

Background

This dilemma arises because a plant can either invest its resources in defense or in growth, and a plant should prioritize one over the other. Evidence is mounting that plants downregulate their defense in favour of competitive strength. A plant that receives a low red:far-red ratio - an indication of forthcoming competition for light - becomes less sensitive for hormones involved in defense (jasmonic acid and salycic acid).

The adaptive significance of this downregulation is not well understood. And although this downregulation may be advantageous in an ecological setting, it may be disadvantageous in agricultural setting.

In agriculture, plants grow at high density and hence they maybe be sub defended. Thus, compromising defense over competitiveness may be a disadvantage in this context. Therefore, one outstanding question is whether plants vary in the extent to which they downregulate defences upon reception of lower red:far-red ratios. For example, do genotypes that are less sensitive to a decreased red:far-red ratio have higher defense levels compared to genotypes that are responsive to a decreased red:far-red ratio?

Another question is more fundamental: what are the consequences in terms of fitness if a plant downregulation its defenses by far-red in high density? This question could be answered through modelling.

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