A unique genotype of the rust pathogen, Puccinia psidii, on Myrtaceae in South Africa

Abstract

The rust pathogen, Puccinia psidii, was first detected in South Africa in 2013 on a single non-native ornamental Myrtus communis tree. This prompted surveys of the country to determine its geographic distribution and host range. Previously developed microsatellite markers where used to characterize the genetic diversity of P. psidii isolates collected from these surveys. In addition, artificial inoculation studies and field observations were used to evaluate the susceptibility of native Myrtaceae to infection by P. psidii. The pathogen was found on native Myrtaceae in isolated natural situations and it was also common on exotic Myrtaceae in nurseries and gardens. Marker analysis showed that a single genotype of the rust is present in South Africa and that this is different to the so-called Bpandemic^ strain recorded in countries outside Brazil. It was found to have a broad distribution in South Africa with collections as far as 1500 km apart. The data provide firm evidence for a single introduction of the pathogen from an as yet unkown source. Its wide distribution, particularly in relatively isolated natural areas, suggests that P. psidii has been present in South Africa for much longer than implied by its first detection in the country.