Genetic resources and selection methods for drought and salinity resistance in durum wheat
The relevance of drought and salinity stress under Mediterranean conditions is reviewed and prospects for crop improvement against these constraints are discussed. Field trials under severe drought in Syria highlighted the importance of earliness to ensure satisfactory yields. Peduncle length and frost tolerance were also important attributes. Under more favourable conditions in Sicily, the yield components per se (number of spikes, number of kernels and kernel weight) had greater influence on genotype performance. At both locations of evaluation high yields were attained through different architectures of traits. Durum wheat genetic resources proved very variable. Genotypes were identified which could be used as donors of adaptive characters in breeding programmes. The CERES-Wheat growth model was used for the two locations, using historical weather data and two genotypes of known adaptation to the region. Early heading was a positive attribute, particularly in Syria. At both sites, lengthening of the grain filling period resulted in higher yields. Three sowing dates were simulated. "Early" sowing (1 November) had the highest simulated yield in both environments, suggesting a possible agronomic means to improve yields under stress. Simulated yields were in most cases within 15% of measured values when a comparison was possible. The ability to adjust osmotically was sought in seedlings artificially exposed to drought stress during early development. One entry appeared to possess this feature. However, another genotype, of known tolerance under real conditions, did not show this ability. Therefore, osmotic adjustment during early stages of ontogeny does not seem unequivocally able to identify the best genotypes under drought. Salt tolerance of durum wheat genetic resources was assessed measuring early growth under controlled environment. The data indicated that the results may be somewhat experiment-specific when using different growing techniques such as hydroponics and sand-culture. Finding tolerant tetraploid entries in terms of plant survival and ion uptake seemed difficult. However, variability existed and some entries, less susceptible than others, were noted. They could be used for breeding. For instance, they could be valuable recipient for the introgression of identified resistance mechanisms from other taxa.