A comparison of the direct and indirect defence abilities of cultivated maize versus perennial and annual teosintes

The transition from a perennial to an annual life cycle, as well as domestication, are expected to increase plant growth and reproduction at the same time that anti-herbivore defences are reduced. Here, we investigated the effects of the life-history transition (the perennial teosinte Zea diploperennis to the annual teosinte Z. mays ssp. mexicana) and domestication of Zea (annual teosinte to the modern maize Z. mays ssp. mays) on direct and indirect defences against the fall armyworm Spodoptera frugiperda. The direct defence of Zea was assessed by larval survival and nutritional indices based on food intake and utilisation. Indirect defence was measured in terms of the olfactory preference of the night-active predatory earwig Doru luteipes for nocturnal herbivore-induced plant volatiles (HIPVs) from the teosintes and maize. Larval growth and survival were reduced on teosintes relative to maize. Whilst larvae fed on perennial teosinte had lower food intake indices, those on annual teosinte showed lower food utilisation indices relative to maize. The earwig preferred HIPVs emitted by teosintes over those by maize, but it did not discriminate between odours of herbivore-damaged annual and perennial teosinte. The nocturnal HIPV blend from maize contained the lowest total amount of fatty acid derivatives, while it had higher total amounts of terpenes compared to teosintes. Our study shows that the teosintes are better defended than maize in terms of direct and indirect defences; however, the perennial teosinte have stronger direct defences against the fall armyworm than the annual teosinte.