IDENTIFICATION OF RESISTANCE SOURCES TO SEPTORIA TRITICI BLOTCH IN OLD TUNISIAN DURUM WHEAT GERMPLASM APPLIED FOR THE ANALYSIS OF THE ZYMOSEPTORIA TRITICI-DURUM WHEAT INTERACTION

Septoria tritici blotch (STB) caused by the fungus Zymoseptoria tritici (formerly known as Mycosphaerella graminicola) is currently the most important foliar disease of durum wheat (Triticum turgidum subsp. durum) in Tunisia, causing serious yield losses and affecting grain quality. Resistance breeding in durum wheat to STB can provide an effective, economic and environmentally-safe strategy to reduce yield losses. However, this is hampered by a lack of resistance sources, and a limited understanding of Z. tritici pathogenicity. Here, we report the identification of nine resistant accessions to STB upon field inoculation of 144 old local durum wheat accessions with a virulent isolate TunBz-1. Crosses between the resistant accessions and evaluation of F-2 progenies for their reaction to TunBz-1 led to the identification of four new resistant genes, associated with Azizi27, Agili37, Agili39 and Derbessi12 landrace accessions. Random distribution of the resistant accessions in an AFLP based-dendrogram of 123 old durum wheat accessions suggested independent resistance gene-evolution. Based on the identified resistance sources, the analysis of the virulence spectrum of 55 Z. tritici isolates collected from different durum wheat-growing regions in Tunisia showed a highly significant genotype-by-isolate interaction. Furthermore, pathotype variability among Z. tritici isolates was low as the isolates were classified into two groups (I and II) that showed differential reaction on the accession Azizi27. Our results show that the old local durum wheat germplasm might harbor novel resistance genes that can be deployed in durum wheat breeding programs.