Landscape Genomic Tools Can Inform Future Rootstock and Farmland Selection for an Agricultural Tree Nut From Its Wild...

Climate change is threatening crop yield of a broad range of agricultural species, impacting global food security and trade. Crop wild relatives may contain climate adaptations that can be quickly introduced into cultivars, especially in perennial tree crops that use rootstock. Identifying climate resilient genotypes that can potentially be used as alternative rootstock is imperative to mitigate the impacts of climate change. Here, we used whole genome sequence data of 59 wild Juglans hindsii (Northern California black walnut) and 39 wild J. californica (Southern California black walnut) adult trees to: (i) determine predicted adaptedness to future climate based on landscape genomic models, (ii) explore their adaptedness if used as rootstock in existing walnut orchards and (iii) identify potential future planting sites within existing croplands. Wild J. hindsii has the highest predicted adaptedness to the future climate of Northern and Central California walnut orchards, while wild J. californica has the highest predicted adaptedness to Southern and Central California walnut orchards. Juglans californica has high adaptedness to the future climate of more existing cropland than J. hindsii does. If walnut farmers wanted to test new rootstock sources for their existing orchards or convert their farmland into walnut orchards, this study informs the exploration of such ideas. We illustrate how landscape genomic tools can be utilized in agricultural contexts as first steps in identifying climate adapted genotypes.