Estimating heritability of disease resistance and factors that contribute to long-term survival in butternut (Juglans cinerea L.)

Abstract

For most wild species affected by exotic pests or pathogens, the relative importance of heritable genetic differences in determining apparent variation in disease resistance is unknown. This is true in particular for butternut, a North American hardwood affected by butternut canker disease and undergoing demographic contraction. Little is known about site effects on butternut decline, in part because long-term monitoring data are lacking. We collected detailed disease phenotypes and multilocus microsatellite genotypes for all surviving individuals in a large natural population of butternut in 2003 (n= 302) and 2012 (n=113). Two analytical methods, correlations between pairwise phenotypic similarity and pairwise relatedness, and estimation of among-family variance, both indicated weak heritability of disease-related traits and no heritability for overall tree health in the population. Additionally, an analysis of spatial data collected in 2001 (n=341) and 2012 (n=113) demonstrated that drier, upland sites contribute to increased likelihood of survival. We conclude that genetic differences among wild butternut individuals contributed little to observed variance in survival over 10 years but fine-scale site differences were useful predictors of butternut mortality.

Regional patterns of declining butternut (Juglans cinereaL.) suggest site characteristics for restoration

“…Although there may be some variation in the heritability of resistance, there are no studies demonstrating heritable resistance to butternut canker disease. One study demonstrated little genetic basis for observed differences in mortality (LaBonte, Ostry, Ross‐Davis, & Woeste, ). Instead, LaBonte et al.…”

“…Instead, LaBonte et al. () concluded that localized site conditions were more useful predictors of butternut mortality with greater survival in drier, upland sites.…”

“…These sections are located in eastern Minnesota and western Wisconsin (Figure ). Furthermore, based on other literature on butternut canker impacts (LaBonte et al., ), restoration of butternut is likely to be most successful on dry, upland sites within forest stands with the aforementioned ecological characteristics. The stands with surviving butternut also could be used to study butternut regeneration and disease epidemiology.…”

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

“…The present study, in contrast, included seeds propagated from long-term surviving selections collected from across a wide geographic range and inter-pollinated together in a grafted orchard, expanding the genetic diversity of our test families. Additionally, our study did not include environmental and site factors as in Labonte et al (2015), so a comparison with the current study's results on heritability of BCD tolerance in hybrids is not entirely possible.…”

“…With differing levels of aggressiveness, the specific isolates present within a certain location may contribute, in part, to help explain why some areas experience more severe and sudden BCD outbreaks than others (Broders et al, 2015;Morin et al, 2017). However, it is likely that habitat and environment also play a strong role in determining occurrence of infection in these situations as well (Boraks and Broders, 2014;Labonte et al, 2015;Morin et al, 2017).…”