Effect of Three Tillage Systems on Weed Flora in a 3-Year Rotation with Four Crops

Nineteen accessions belonging to six tetraploid wheat species were evaluated and compared for carbon isotope discrimination and grain yield during two successive cropping seasons (1995 and 1996) under Mediterranean rainfed conditions. The two seasons differed markedly in precipitation regime. A wide variation for the measured traits was observed among the 19 accessions for carbon isotope discrimination and grain yield in both years. Significant differences were also noted between species accessions for A and grain yield. In both years. Triticum timopheevi (AC genome) showed lower (delta) values than the other tetraploid species (all carrying the AB genome). Positive correlations were observed between A and grain yield in both years. The use of carbon isotope discrimination as an indirect selection criterion for yield under stress and the potential benefits of some alien tetraploid species in improving drought tolerance in durum wheat arc discussed.