Abstract
Oat crown rust, caused by Puccinia coronata f. sp. avenae, is considered the most widespread and damaging disease of oat (Avena sativa) in Tunisia. The virulence structure of the natural oat rust population in Tunisia was studied in four areas from 2002 to 2007 using Puccinia coronata resistance genes (Pc-genes). The areas are located in northern Tunisia: Afareg, Bourbia, Sedjnen and Ariana. In this survey Pc38, Pc39 and Pc68 showed a high level of resistance to natural oat crown rust. But the most important finding in 2004 in Ariana was that the rust was virulent on Pc68 (IT '4'). Moreover, in 2002 Sedjnen survey, there was a high degree of virulence to Pc39 (IT '3'). In the other areas and other years, Pc68 and Pc39 were highly resistant to natural oat crown rust. Only Pc38 showed a stable high level of resistance to natural oat crown rust in all four areas and during the six years of the study. Areas showing a high degree of similarity were Sedjnen and Afereg (SI=4.5). Ariana and Bourbia showed little similarity to the other areas, and had the greatest dissimilarity to each other (SI=11.30). The virulence phenotypes of the P. coronata natural population in Tunisia are certainly influenced by the alternate host, Rhamnus lycioïdes which is abundant in the mountains of northwestern Tunisia. A combination of the Pc38, Pc39 and Pc68 genes will provide a high level of durable protection from crown rust in Tunisia.