Variation in induced defense against caterpillars among ancestral and derived Zea plants

Herbivores are persistent and destructive pests in commercial agriculture. Some plants, notably the more wild phenotypes, have natural defenses against herbivores and diseases. Species in the genus Zea range from primitive weeds with very small seeds to the high yielding Zea mays ssp. mays used in agriculture. We compared the induced defenses to caterpillars of four different species/lines of Zea: Z. diploperennis, Z. mays ssp. parviglumis from two different locations, and Z. mays ssp. mays. We infested the different species/varieties of Zea with fall armyworms (Spodoptera frugiperda) and measured the growth of the armyworms after two weeks. Fall armyworms fed Z. diploperennis and Z. mays parviglumis from Talpitita were smaller and grew slower than the caterpillars feeding on Z. mays parviglumis from San Lorenzo and Z. mays mays. To measure plant response, we used qPCR to quantify expression levels of three genes associated with induced defense against insects in corn and other plants (wip1, hag, and pr1) at 2, 24, and 36 hours after exposure to fall armyworm herbivory. Higher levels of defense gene expression were found in the ancestral Zea (Z. diploperennis and Z. mays ssp. parviglumis) than in the more derived Zea plants. Our results suggest that if resistance genes such as wip1 could be re-incorporated into the genome of modern corn, we could substantially increase the resistance of these plants to caterpillars.