Non-target effects of transgenic blight resistant American chestnut, Castanea dentata (Marshall), on a seasonal guild of lepidopteran folivores

Chestnut blight, Cryphonectria parasitica (Murrill) Barr, an exotic fungal pathogen, eliminated American chestnut, Castanea dentata Marshall as a foundational species and canopy dominant across its range. While conventional breeding for resistance has had little success, genetic engineering of chestnuts with a patented gene construct expressing oxalate oxidase (OxO) has produced blight resistant strains that appear to retain the morphological characteristics prized in American chestnut, thus providing hope for this heritage tree.  Consideration of potential non-target effects of transgenic trees is critical prior to broad release into natural environments, as this is the long-term objective of the restoration program. However, transgenesis can have unintended effects on non-target species directly through expression of gene products or through pleitropic effects on other genes. To evaluate non-target effects on insect herbivores, we used several folivorous Lepidoptera and conducted short-term relative growth rate (RGR) bioassays.  We utilized five cloned trees from eight cultivars including three transgenic OxO events, a promoter only event, two pure American chestnut genotypes, a pure Chinese chestnut (C. mollissama Blume), and a conventionally backcrossed American x Chinese blight resistant hybrid.  In both 2010 and 2011, gypsy moth (Lymantria dispar L.) had higher RGR on transgenic lines. However, in 2012, four herbivores spanning the growing season (forest tent caterpillar (Malacosoma disstria Hbn), gypsy moth, polyphemus moth (Antheraea polyphemus (Cramer)), and fall webworm, Hyphantria cunea Drury, exhibited no difference in growth among cultivars.  In this study and in prior assays utilizing different blight resistant events, positive or negative non-target effects have been minimal for an array of foliage feeding Lepidoptera.