Photo Credit: Dave Hodson, CIMMYT
Following the localized stem rust epidemics in Ethiopia on the cultivar “Digalu” in 2013/14 (see report 23rd Dec 2013); continued, severe stem rust outbreaks have been observed in the 2014/15 main season. Once again the popular cultivar “Digalu” has been seriously affected in several areas. Overall, at least 20 districts were considered to be affected to some extent by the Digalu epidemic. Complete crop loss has occurred in the worst affected areas. Race TKTTF (known as the “Digalu” race in Ethiopia) has been identified as the causal race for the 2014/15 outbreaks (the same as in 2013/14). Virtually all samples analyzed from 2014/15 have proven to be race TKTTF and this race now totally dominates the stem rust population in Ethiopia. This race is NOT related to the Ug99 race group; it was first detected in Ethiopia in Aug 2012 (1 sample only, trace levels) but then went undetected until it caused severe localized epidemics during Nov 2013 to Jan 2014. The same race is known from several countries in the Middle East and that region is a presumed likely origin. Virulence on the resistance gene SrTmp is considered the main factor behind the complete susceptibility of the cultivar “Digalu”.
The first stem rust outbreaks in Ethiopia were recorded in West Shewa (about 100 km to the west of Addis Ababa) in early September 2014. Digalu exhibited very high stem rust incidence and severity (both up to 100%) and severe losses resulted on unsprayed fields. Two districts were initially affected, but over time the outbreak spread to cover 5-7 districts in this area. Subsequent outbreaks were recorded in October to December 2014 and these have continued into Jan 2015, with the Arsi Robe area and Bale zone (notably Sinana district) experiencing severe outbreaks with complete crop loss in many fields.
Map 1: Overview of Rust Situation Ethiopia 2014/15
yellow rust also caused localized problems during the 2014/15 season. In Amhara region, 4 zones (East Gojam, South Gonder, North and South Wollo) were affected, with South Wollo experiencing the worst outbreaks. Local triticale’s and the known susceptible variety Kubsa were the most badly affected. Aggressive yellow rust outbreaks also occurred in Bale zone, with some newly released varieties showing susceptibility. Analysis is on-going to determine the causal race.
An overview of the stem and yellow rust outbreaks in Ethiopia during 2014/15 is given in Map 1.
A broad spectrum of different agencies, both national and international, worked tirelessly to control and mitigate the rust outbreaks in Ethiopia in 2014/15. These efforts were successful in many areas and very good crop performance was observed. However, in some areas no, or limited, control was achieved and serious losses resulted (see photos). The 2014/15 situation in Ethiopia is a stark reminder of the extreme difficulties in trying to successfully control stem rust when large areas are planted to highly susceptible cultivars, a virulent pathogen is present and environmental conditions are suitable. Replacement of the highly susceptible cultivars is now the highest priority for Ethiopia.
Photo Credit: Wubishet Alemu (Sinana Agricultural Research Centre)
Photo Credit: Wubishet Alemu (Sinana Agricultural Research Centre)
The huge stem rust inoculum load generated in Ethiopia during 2014/15 is a threat and concern for neighbouring countries and also for future seasons in Ethiopia. Spore dispersal modelling undertaken by the Epidemiological Modelling Group at Cambridge University, UK indicated that most spores were likely to be distributed in a south-westerly direction towards Kenya, Uganda and possibly Rwanda. These countries should be vigilant for the incursion of race TKTTF and any varieties protected by the SrTmp gene should be closely monitored.