Seed germination and seedling vigor of weevil-damaged acorns of red oak

Abstract

Acorn weevils (Coleoptera: Curculionidae) are well-known predators of oak acorns in the eastern hardwood forest region of the United States. We examined the germination percentage of seeds, as well as the physical characteristics of seedlings, originating from both weevil-damaged and sound acorns of red oak ( Quercus rubra L.) to determine if weevil depredation impacts seedling vigor. Seeds were grown under greenhouse conditions for a period of 8 weeks. X-ray imaging was used as a nondestructive method for determining seed condition prior to germination. The combined data set showed a reduction in germination percentage from 86% for sound acorns to 26% for those damaged by weevils. Seven seedling metrics were evaluated for differences between seedlings originating from sound and those from weevil-damaged acorns. Of these metrics, the number of leaf flushes, total number of leaves, root collar diameter, shoot length, and dry mass were significantly (P < 0.05) different. Two variables, root length and shoot diameter, were not significantly different. Early allocation of resources to root establishment likely explains these findings. Because of reduced stem height and leaf number, seedlings from weevil-damaged acorns are likely to be less competitive in the forest understory than those from sound acorns.