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

Abstract

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.

Altitude is the main driver of coffee leaf rust epidemics: a large-scale survey in Ethiopia

“…Changes in crop management practices during the last three decades have been linked to the emergence of CLR in Ethiopia, including the widespread use of high yielding but CLR-susceptible varieties grown in poorly managed plantation systems largely adopted at the lowlands (Jefuka et al 2010). Most notably, the effect of altitude which explained most of the variation in CLR intensity in our survey, was expected given its known effect on epidemic components such as infection efficiency and duration of the latency period (Bock 1962;Kushalappa 1989;Brown et al 1995;Daba et al 2018;Garedew et al 2019). Several studies conducted elsewhere, including Ethiopia, have…”

“…shown that CLR severity tends to decrease with the increase in altitude where the fields experience relatively lower night time temperatures (Wondimu 1991;Hindorf and Omondi 2011;Daba et al 2018;Garedew et al 2019). In Central America, prior to the epidemics recorded in Guatemala during the early 2010s, CLR was less likely to occur at production sites above 1,000 m, where cooler night and daytime conditions decreases infection efficiency and extends the latency period (Avelino et al 2015).…”

“…In Rwanda, CLR severity was estimated to decrease 1.5% percent unit per each 100 unitary increase in altitude (from 1400 to 1800 m) (Bigirimana et al 2012). In experiments conducted in the Setema district of Jimma Zone, Ethiopia, CLR severity was highest (16.9%) at the lowland and lowest (5.7%) at the highlands irrespectively of the cultivar (Daba et al 2018).…”

“…The increasing importance of coffee for the Ethiopian economy was the main driver of the recent shifts from local to improved, high-yielding, cultivars together with other cropping practices that may promote and suppress epidemics (Avelino et al 2006;Jefuka et al 2010). In general, changes in site selection (lower vs. higher altitude), cropping practices, and seasonal weather have been associated with the emergence of CLR epidemics in Ethiopia (Garedew et al 2019;Daba et al 2018). This hypothesis is based on empirical observations at specific regions.…”

“…The current national status of CLR epidemics is yet to be documented, especially the geographical and altitudinal variation in disease intensity. It is well known the major role that seasonal weather/environmental plays the risk of CLR epidemic, mainly temperature, rainfall and humidity, which affect pathogenic processes such as infection, colonization and sporulation (Daba et al 2018). CLR emergence in Ethiopia has also been associated with changes in temperature and rainfall patterns (Davis et al 2012;Garedwe et al 2019).…”