Berberis holstii is functional as an alternate host of Puccinia graminis in Ethiopia
Berberis holstii, native to the highlands of East Africa, is susceptible to Puccinia graminis and P. striiformis in artificial inoculations. However, it is not known whether these pathogens complete their sexual cycles in the region. In an attempt to understand the role of B. holstii in pathogen variation and epidemiology of wheat stem rust and stripe rust, we investigated the functionality of B. holstii as an alternate host. Natural aecial infections on B. holstii were observed and sampled in August at Mt. Kenya and Narok (Kenya), and June to December at North Shewa (Ethiopia) from 2008. Aeciospores from the collections were inoculated to a panel of cereal species, including Line E and ‘Morocco’ wheat, 'Hiproly’ barley, 'Prolific' rye, and ‘Marvelous’ oat. For the majority of aecial samples, aeciospore viability was lost during shipment and storage; thus inoculations were not successful. Inoculations using relatively fresh samples collected at North Shewa in 2012 and 2014, resulted in stem rust infections on Line E, Prolific, Hiproly, and Marvelous. DNA assays using real-time PCR confirmed the presence of P. graminis in these samples. While it is likely that the pathogen infecting Line E, Prolific and Hiproly is P. graminis f. sp. secalis (Pgs), the inoculation and DNA assays did not provide sufficient resolution to distinguish Pgs from Pgt. Stem rust infections on Marvelous were assumed to involve Pg f. sp. avenae. Experiments are in progress to characterize isolates derived from these samples, and to determine if other rust fungi are present in these samples. Based on these preliminary data, we conclude that P. graminis completes its sexual cycle in Ethiopia. The contribution of the sexual cycle to the observed variation within the Pgt population in the region remains unclear.