In the mid to late 1800s, Colorado was a hotspot for apple agriculture, and vestiges of this era can be found across Boulder Open Space and residential Boulder County. By 1870, agriculture was so widespread in Boulder County, that it was deemed the second most agriculturally “improved” county in Colorado, despite its relatively small size. The advent of the canal system in Boulder allowed farmers to successfully introduce apples in the 1860s. The industry's success waxed and waned throughout its 150-year history, and many relic trees remain; feral apple trees have also established themselves in the county. According to Orchard Survey of the Northeastern District of Colorado from 1922, there are 36 different varieties of apple trees described in Boulder County. Historically, the most common apples in Boulder County were the Ben Davis, Jonathan, Wealthy, and Delicious cultivars. Of apple cultivars recorded in Boulder County within the last century, few have genomic data available.
In this paper, we describe apple varieties found in Boulder County using genomic analyses of apple leaf tissues, and seek to answer the following question: Do the apple and crabapple trees in Boulder County reflect multiple independent introductions of apple trees? We hypothesized that the nuclear genomes of local Malus sp. trees will reflect many ancestral groups. Ultimately, cataloguing the genomic information of these apples is important as climate change might threaten their ability to persist in the Front Range. Rapidly changing local conditions may result in the loss of the heirloom strains that have been adapted to historic conditions in Boulder County. Describing the genetic diversity of existing cultivated and feral apple trees is important to preserve Boulder history and diversity in the face of climate change.