Seasonal and altitudinal differences in coffee leaf rust epidemics on coffee berry disease-resistant varieties in Southwest Ethiopia

Coffea arabica is native to the Afromontane forests of southwestern Ethiopia, the leading African country in Arabica coffee production. The intensity of coffee leaf rust (CLR), a fungal disease of growing concern to coffee farmers, was assessed in eight coffee berry disease-resistant C. arabica varieties planted at three different altitudes. Disease variables assessed were CLR prevalence (percent of infected plants), incidence (percent rusted leaves) and severity (percent leaf area affected) at four times within a year (Nov, Jan, Apr and Jun). The intensity of CLR epidemics was highest at the lowland and lowest at the highland location. We hypothesize that inoculum may be limited by cooling conditions that negatively affects fungal sporulation. CLR intensity was highest at harvest time (Nov) and decreased during the following dry season, reaching zero values in Apr and Jun. All coffee varieties were similarly susceptible to CLR. Our data suggest that more efforts should be employed by breeders to develop CLR-resistant coffee varieties, and that shifting cultivation from lower to higher altitudes may contribute to achieve to higher yields due to lower impact of CLR epidemics.