Several Seiridium species (Sporocadaceae: Xylariales) cause cypress canker in South Africa

Abstract

Cypress canker is an important fungal disease caused by at least seven different Seiridium species. The disease has been known on Cupressaceae trees in South Africa since the 1980's, but its relevance was recently accentuated with an outbreak on native Widdringtonia nodiflora trees in the Western Cape. The causal agent, S. neocupressi, was previously unknown in the country, highlighting a lack of information regarding the disease in South Africa. The aim of this study was to investigate the occurrence of cypress canker and its causal agents across the country by sampling diseased Cupressaceae trees and reconsidering the identity of Seiridium strains previously collected in the country. Phylogenetic analyses revealed five known cypress canker pathogens and two putatively novel species. Seiridium cardinale was the most frequently isolated species in the Western Cape. Only two isolates of S. neocupressi were found outside the outbreak on Widdringtonia. Seiridium unicorne was most frequently isolated in the Gauteng and Free State provinces. Seiridium cancrinum, S. kenyanum and the two undescribed species were each recovered only in localised areas. Stem inoculations on x Hesperotropsis leylandii using S. cardinale, S. neocupressi and S. unicorne strains confirmed the pathogenicity of S. cardinale and S. neocupressi. In contrast, S. unicorne strains exhibited variable levels of aggressiveness. This study represents the first extensive consideration of cypress canker in South Africa and one of few studies on this important disease in the Southern Hemisphere