A Molecular Survey of the Occurrence of Coffee Berry Disease Resistant Coffee Cultivars Near the Wild Gene Pool of Arabica Coffee in Its Region of Origin in Southwest Ethiopia.

Abstract

Cultivation of crops close to their wild relatives may jeopardise the integrity of wild genetic resources. Detecting cultivars among wild plants is necessary to characterise crop-wild gene flow, but can be challenging if cultivars and wild plants are phenotypically highly similar. Genomics tools can be used instead, but the selection of diagnostic loci for cultivar identification can be difficult if the wild and cultivated genepools are closely related. In Ethiopia, Arabica coffee cultivars resistant to coffee berry disease (CBD) occur near wild Coffea arabica plants and local landraces. However, the abundance and distribution of these cultivars across coffee sites remains unclear. Here, we present a new module of the SMAP package called SMAP relatedness pairwise to characterise pairwise genetic relationships between individuals based on haplotype calls and to identify diagnostic loci that distinguish (sets of) individuals from each other. Next, we estimate the relative abundance of CBD-resistant cultivars across 60 Ethiopian Arabica coffee sites using a genome-wide fingerprinting approach. We confirm the presence of these cultivars in around 75% of the coffee sites with a high agreement between a field survey and our DNA fingerprinting approach. At least 20 out of 60 sites with supposedly wild C. arabica individuals contain signatures of the cultivated genepool. Overall, we conclude that CBD-resistant cultivars are widespread in Ethiopian coffee sites. The development of SMAP relatedness pairwise opens opportunities to assess the distribution of coffee cultivars in other regions in Ethiopia and to apply similar screenings near wild relatives from other crops.