Weevil seed damage reduces germination and seedling growth of hybrid American chestnut

Abstract

Seed predation by weevils (Coleoptera: Curculionidae) has been implicated as a limiting factor in oak recruitment throughout eastern US forests. We examined the effects of weevil seed predation on American chestnut (Castanea dentata (Marsh.) Borkh.). Although an introduced pathogen eradicated sexually reproducing populations of American chestnut in the early 1900s, the recent development of a blight-resistant hybrid makes reintroduction feasible. We nondestructively assessed the amount of weevil damage to seeds using X-ray imagery and traditional float test methods in American and blight-resistant hybrid chestnut. We quantified the effects of weevil damage on seed germination and seedling growth. The float test method misidentified damage for up to 50% of seeds, whereas the X-ray method misidentified only 3% of the sample. Germination declined with damage: the smallest damage level reduced germination from 94% to 32%. No seeds with >50% damage germinated. Weevil damage reduced seedling growth by 50% compared with undamaged seeds. Seedling size increased with seed size, but seed size had no effect on germination. Our results highlight the importance of orchard and seed processing practices that prevent weevil damage to chestnut seeds. Because they drastically reduce germination rates and seedling growth, weevils have the potential to limit seed regeneration and dampen rates of spread in populations following reintroduction.