Uncoupling direct and indirect plant defences: Novel opportunities for improving crop security in willow plantations

Abstract

Increased cropping security, i.e. minimized risk for detrimental stress events and hence improved yield stability, may be achieved by selecting resistant plant genotypes. However, strong direct defences against herbivores have been associated with negative effects on the natural enemies, resulting in weak indirect defences through these plant “bodyguards”. We compared the preference and performance of the most detrimental herbivore, the leaf beetle Phratora vulgatissima, and a biocontrol agent, the predatory bug Anthocoris nemorum, on four willow (Salix) genotypes used in short rotation coppicing. The biocontrol agent is omnivorous and survives on the plant in the absence of prey, without causing any apparent damage to the plant. Two of the genotypes intrinsically attracted and supported the bodyguard, and were at the same time partially capable of deterring and resisting the herbivore. In contrast, the third willow clone exhibited very limited direct and indirect resistance, while the fourth clone displayed intermediate levels of both. Thus, direct and indirect defence against herbivores need not be traded off in this system, but may be intertwined, resulting in “super plants” with higher probability of resisting detrimental herbivores, opening up novel possibilities for increased cropping security, without the use of insecticides.