AUTHOR=Brennan Andrea N. , McKenna James R. , Hoban Sean M. , Jacobs Douglass F. 

TITLE=Hybrid Breeding for Restoration of Threatened Forest Trees: Evidence for Incorporating Disease Tolerance in Juglans cinerea

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.580693

DOI=10.3389/fpls.2020.580693

ISSN=1664-462X

ABSTRACT=<p>Hybridization is a potential tool for incorporating stress tolerance in plants, particularly to pests and diseases, in support of restoration and conservation efforts. Butternut (<italic>Juglans cinerea</italic>) is a species for which hybridization has only recently begun being explored. This North American hardwood tree is threatened due to <italic>Ophiognomonia clavigignenti-juglandacearum</italic> (<italic>Ocj</italic>), the causal fungus of butternut canker disease (BCD), first observed in 1967. Observational evidence in some wild <italic>J. cinerea</italic> populations indicates that naturalized hybrids of <italic>J. cinerea</italic> with Japanese walnut (<italic>Juglans ailantifolia</italic>) may be more tolerant to BCD than non-admixed <italic>J. cinerea</italic>, but this has not been formally tested in a controlled trial. We aimed to examine potential BCD tolerance within and between <italic>J. cinerea</italic> and <italic>J. cinerea</italic> × <italic>J. ailantifolia</italic> hybrids and to determine if there is a difference in canker growth between BCD fungal isolates. Five-year-old <italic>J. cinerea</italic> and hybrid trees were inoculated with two <italic>Ocj</italic> fungal isolates collected from natural infections found in two different sites in Indiana, United States, and a blank control (agar only). Measurements of both artificially induced and naturally occurring cankers were taken at 8-, 12-, 20-, 24-, and 32-month post-inoculation. Differences in canker presence/absence and size were observed by fungal isolate, which could help explain some of the differences in BCD severity seen between <italic>J. cinerea</italic> populations. Smaller and fewer cankers and greater genetic gains were seen in hybrid families, demonstrating that hybrids warrant further evaluation as a possible breeding tool for developing BCD-resistant <italic>J. cinerea</italic> trees.</p>