Resistance to butternut canker disease is influenced by disease level and hybridization

Authors: CONRAD, ANNA - Us Forest Service (FS); EBRAHIMI, AZIZ - Purdue University; Fetter, Karl; WARREN, JAMES - Us Forest Service (FS); PIKE, CAROLYN - Us Forest Service (FS); KELL, CALEB - Purdue University; MCKENNA, JAMES - Us Forest Service (FS); WILLIAMS, MARTIN - Canadian Forest Service; FARADONBEH, MOJTABA - Purdue University; JACOBS, DOUGLASS - Purdue University

Submitted to: Canadian Journal of Forest Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: The butternut (Juglans cinerea) is a native species of walnut that is rapidly declining due to an invasive fungal pathogen (Ophiognomonia). The tree is listed as a critically endangered species. In this study, we screened a range-wide collection of over 300 butternut and hybrid butternut families for resistance to butternut canker disease, a disease which has decimated butternut across its range from the southeastern United States to southeastern Canada. Our study demonstrates that disease severity and incidence is influenced by site conditions. In addition, we determined that resistance is heritable, but disease pressure at the screening site influences the level of heritability. Prior to our study, it was assumed that butternut was generally not resistant to butternut canker and the use of hybrid butternut has been proposed as a strategy for butternut restoration. Our study demonstrates that while the most resistant families are hybrid butternut, some butternut families show a modest level of disease resistance. Therefore, we propose that future butternut restoration efforts should take into consideration not only resistance level but site conditions when deciding where and when to plant butternut or hybrid butternut.

Technical Abstract: Butternut (Juglans cinerea) populations have been decimated due to butternut canker disease (BCD). To date, much of the observed disease resistance in butternut occurs in hybrids with Japanese walnut (J. ailantifolia), a non-native species which was introduced to the US and naturally hybridizes with butternut. In this study we screened over 300 open-pollinated families for resistance to BCD. Trees were planted in Indiana, US, in two areas (one with high disease levels and one with low disease levels) and allowed to become naturally infected. After 10 years, trees were rated for resistance using a five-point scale. Trees were genotyped to confirm their ancestry, since complex hybrids occur naturally and can be difficult to distinguish morphologically. We used logistic regression to evaluate factors, like ancestry (e.g., hybrid or butternut), on the probability of resistance. Across all sites, ancestry was a significant predictor of resistance. Our results also demonstrate that resistance is heritable on high disease sites, but not on low disease sites. While the most resistant families are hybrid, some butternut families do show a modest level of resistance based on estimated breeding values for each family. Variation in disease level across plantings highlights the importance of considering site influence on disease development as part of butternut resistance screening programs. Identifying sites less conducive to disease development may aid in butternut conservation and restoration.