Isolation of a natural solopathogenic strain of Sporisorium reilianum f.sp. zeae (Ustilaginaceae, Basidiomycetes).

Sporisorium reilianum f.sp. zeae (Kühn) Langdon and Fullerton (Basidiomycota, Ustilaginaceae) is the causal agent of head smut of maize and sorghum. The parasitism is initiated by the fusion of two compatible sporidia which give rise to the formation of dikaryotic pathogen hyphae. However, in Ustilaginaceae, some fuzzy diploid strains could also be formed. These strains are solopathogen as they can infect a host in absence of crossing with a compatible haploid sporidia. A solopathogenic strain of S. refilianum was obtained using an original protocol. Sporidia were isolated from germinated teliospores and spread on solid medium to identify stable fuzzy solopathogenic strain. Confocal observations of the solopathogenic strain (SRZS1) after nucleus staining with propidium iodide indicates that they are formed by rounded shape cells which are monokaryotic. A CAPS approach was used to analysis the matb gene of S. reilianum. The presence of two matb loci in SRZS1 showed that this monocaryotic strain is diploid. The pathogenicity of SRZS1 was investigated by maize infection. Our results confirmed that SRZS1 is infectious, induces some typical symptoms in maize but could not sporulate and form sori.