Breeding for Coffee Leaf Rust Resilience in Coffea sp

Copyright © 2019 by the American Society of Agronomy 5585 Guilford Road, Madison, WI 53711 USA All rights reserved T he coffee bean is the most important agricultural product in international trade; it ranks second behind petroleum in product exports worldwide. An estimated 15 billion coffee trees are being grown to meet this demand, and the work that goes into this directly contributes to the income of 25 million small producers worldwide (New World Encyclopedia, 2014). Due to the importance of this plant, the appearance of coffee leaf rust (CLR) has led to many social and economic issues that have prompted research into breeding coffee strains that are resilient to the fungus. First recorded in East Africa in 1861, CLR is caused by the fungal pathogen Hemileia vastatrix. It went on to spread throughout the world’s coffee producing countries and became the biggest danger to coffee production. CLR attacks the plant by infecting and then sporulating through the stomata on the under-surface of the leaves. The infection starts at the bottom of the plant and works its way up (Fig. 1). In particular, the infection occurs in areas that collect rainwater. Infections lead to severe defoliation, which causes a loss in the subsequent year’s bean yield. Severe infections can lead to the death of the tree (Arneson, 2011). This disease has had far-reaching impacts since its discovery. Before the 1870’s coffee was grown extensively in Sri Lanka (then Ceylon) until H. vastatrix arrived and decimated the coffee plantations. This led to coffee being replaced by tea, a complete reconstruction of their agriculture sector (Tea Exporters Association Sri Lanka, 2017). A more current impact of CLR is the rise in immigration due to the arrival of the fungus in Central America. Approximately 337,000 jobs and $460 million in income were lost (USAID, 2018). Beyond that, coffee contributes to the income of 125 million people worldwide, from smallholders to large companies. CLR attacks both Coffea arabica (Arabica) and Coffea canephora (Robusta), the two most economically important coffee species (Fig. 2). Arabica is considered the species that produces the highest quality coffee while Robusta is used for instant and filler coffee. A key difference between the two species is that Robusta is allogamous while Arabica is autogamous. In addition all coffee species are diploids Second place Student ManuScript