The rusts of wild rye in South Africa

Abstract

BackgroundSecale strictum subsp. africanum, a self-fertile and perennial wild rye species, is endemic to the Roggeveld Mountains of the south-western Karoo, South Africa. Despite historical abundance on the Roggeveld plateau, S. strictum subsp. africanum is currently threatened with extinction. Many reasons have been given for its decline, including susceptibility to rusts. MethodsLeaves with stem, leaf and stripe rust pustules were sampled from cultivated and naturally occurring S. strictum subsp. africanum on the farm Kanariesfontein near Sutherland. Identity of the rust pathogens was determined through infection and sequencing studies. ResultsInoculation studies showed that stem and leaf rust collected from wild rye were avirulent on bread wheat, but virulent on Secale cereale. The stripe rust specimen was virulent on bread wheat and was identified as Puccinia striiformis race 6E16A−. Using ITS sequencing, the wild rye leaf rust specimen was confirmed as Puccinia recondita, and the stripe rust specimen as P. striiformis. ITS sequences did not distinguish between Puccinia graminis f. sp. tritici and Puccinia graminis f. sp. secalis, respectively the causal organisms of wheat and rye stem rust. Inoculation of wild rye plants with P. graminis f. sp. tritici proved its susceptibility to stem rust races attacking wheat and triticale. ConclusionThis study established that S. strictum subsp. africanum is a host for both rye and wheat stem rust, rye leaf rust and wheat stripe rust.