Drought and flood stress tolerance of butternut (Juglans cinerea) and naturally occurring hybrids: implications for restoration

Abstract

Efforts to restore species threatened by introduced pathogens often include breeding resistance into susceptible native species from resistant exotics, but this is a lengthy and expensive process. Naturally occurring hybrids between susceptible and resistant species may accelerate this process if they fulfill the desired species’ ecological function. To explore this possibility, we exposed the following seedlings to drought and flood treatments in a controlled environment: Juglans cinerea L. (butternut), which has been devastated by an exotic pathogen; Juglans ailantifolia Carr. var. cordiformis (heartnut); Juglans × bixbyi Rehd. [ailanthifolia × cinerea] (buartnut), multigenerational hybrids between butternut and heartnut; and Juglans nigra L. (black walnut). There was a strong taxa × treatment interaction. Butternut had a negative response to flood treatments, expressed by reduced leaf area (LA), photosynthetic assimilation (A), and chlorophyll fluorescence (Fv/Fm). Heartnut had a negative response to drought, expressed by lower LA and A. Hybrid A and LA were reduced in response to both treatments. Results indicate that hybrid drought and flood tolerance may limit their overall ability to completely occupy the ecological niche formerly filled by butternut. However, the strong dichotomous response of progenitors to moisture stress suggests that hybrids could be efficiently screened for J. cinerea character in conjunction with disease resistance.