Microsatellite characterisation of South African <i>Puccinia striiformis</i> races

Abstract

Since the first appearance of wheat stripe rust in 1996 in South Africa, four Puccinia striiformis races have been described. The first detected race, 6E16A−, was proposed to be a foreign introduction from Central or Western Asia that subsequently gained additional virulence through step-wise mutations. Simple sequence repeat markers were used to determine the genetic relationships between the four races, as well as a P. striiformis isolate collected from wild rye and two Kenyan isolates. A single isolate of P. striiformoides collected from Dactylis glomerata was included as an out-group. While the genetic similarity between P. striiformoides and the two Kenyan P. striiformis isolates was low, both shared only 48% genetic similarity with the South African isolates. In contrast, the South African P. striiformis isolates shared at least 74% genetic similarity with each other, with 6E16A−, 6E22A− and 7E22A− being the most similar. A minimum spanning network analysis confirmed this close relationship with several hypothetical intermediates occurring between individual races. This suggests that the South African P. striiformis population is clonal. However, the fact that P. striiformis was introduced into the country suggests that further incursions of more aggressive isolates could occur, which could threaten wheat production in the country.

Keywords: South Africa, SSRs, stripe rust, wheat