Delivering disease resistant cultivars to enhance sustainability of durum wheat production in Tunisia

The significant durum wheat productivity gains made in Tunisia over the last decades through both breeding for higher yield potential and stability and the implementation of improved agronomic practices have often been hampered by severe yield and/or income losses due to biotic constraints in the favorable northern part of the country. Several pathogens affect wheat in Tunisia, with different impacts on yield. Leaf rust, is present in most years, but comes generally late in the season and rarely at yield-limiting levels. However, the main
productivity-threatening biotic constraint in Tunisia is, by far, Septoria Leaf Blotch (SLB). The prevailing strains seem to have developed a unique aggressiveness towards durum wheat. All commercial durum cultivars released previous to 2003 are highly susceptible to this pathogen, and yield losses in excess of 40% are not uncommon in years or environments with average to high rainfall. Extensive screening and crossing work done by the national program, lead to the release of Nasr in 2004, Maali in 2007 and Selim in 2009. All of these three
cultivars have better disease resistance than the widely grown susceptible cultivar Karim. Under heavy epidemics of Septoria tritici, Nasr yields up to 42% higher than Karim. Results from seven years of replicated yield testing (2004-2010) show that Mâali has the highest yield potential of all previously released cultivars and a good level of resistance to SLB, though not as that of Nasr, under favorable conditions in Beja. Its wide adaptation, its good resistance to leaf rust and particularly to lodging put Mâali in the best position to take over significant acreage from Karim. More significant progress was achieved with the most recent release of Selim. This cultivar has shown the best level of resistance to SLB so far and a good resistance to leaf rust. The new generation of Septoria resistant (Nasr and Selim) or less-susceptible (Mâali) cultivars with outstanding agronomic performance is in a strong position to finally take-over from the landmark cultivars of the Tunisian durum “Green Revolution” and provides an opportunity for a more sustainable and hopefully less unstable, national durum production.