Southerly migration of wheat stripe rust race 142E30A+ into South Africa

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), has been effectively managed through cultivar resistance in South Africa (SA) following the first report of the disease in 1996. However, the detection of Pst race 142E30A+ with broader virulence in Zimbabwe during 2018 raised concerns about the potential introduction and establishment of this race in SA through wind mediated urediniospore dispersal. In this study, we characterized Pst field isolates collected in SA, Lesotho, and Zimbabwe through race analysis and microsatellite genotyping. Race-typing of field isolates collected in 2022 revealed the first report of Pst race 142E30A+ in SA, which became predominant and widely distributed across the summer rainfall wheat production region. This race differs from previously reported stripe rust races in SA and Lesotho, being virulent to Yr3a, Yr4a, Yr9, and Yr27. Genotypic analyses confirmed that Pst isolates collected in SA remain clonal, comprising three genetic lineages with low genetic diversity. The close genetic relationship and similar virulence profiles between South African and Zimbabwean isolates of Pst race 142E30A+, together with the timelines of stripe rust outbreaks reported during the 2022 season, support the southerly migration of urediniospores into SA. These findings highlight the threat posed by the emergence and spread of Pst isolates with broader virulence and the need for continued surveillance, early warning systems, and regional collaboration.