Assessing the drought tolerance of Brachypodium ssp. genotypes by agronomic and physiologic indicators

Abiotic stresses including drought (both in terms of quantity and intensity) are serious threats to the sustainability of crop yields accounting for more crop productivity losses than any other factor in rainfed agriculture. Plant responses to water deficit can be analysed by systematically identifying traits that relate to drought tolerance followed by analysis to the cellular, biochemical and molecular levels. Brachypodium ssp, collected from Northern and central Tunisia, was considered as a potential genetic resource of drought resistance for poaceae and forage species. A group of 180 lines of the Tunisian Brachypodium ssp. representative of 9 populations were tested under three watering regimes: watering after two days, watering after four days and watering after six days. Twelve agronomic and physiologic traits were evaluated for their responses to drought stress on the basis of drought response index (DRI). Results show a considerable variation between genotypes and that the majority of traits showed medium (0.3 to 0.5) to high heritability (> 0.6) with low border value for total number of tiller and high border value for the ratio of productive tiller number per total number of tiller and an average value of 0.46. These findings are encouraging from the point of view of the potential for selecting for improved drought tolerance within that species. The method used allows detection after 3 months' growth of material that has the ability to grow at drought conditions which prevent the growth of other material, and the assumption is that they possess enhanced drought tolerance

Morpho-phenologic vs molecular genetic variation in Tunisian Brachypodium spp populations

Brachypodium distachyon belongs to the Poaceae grass subfamily. It has a close genetic relationship with temperate cereal crops which makes it a model for temperate cereals and grass crop. In order to bring a better knowledge on the genetic diversity of this species, 180 lines of B. distachyon representative of 9 populations and 6 eco-regions of Tunisia were characterized on the basis of 18 morpho-phenologic features and 15 microsatellites. Morphological analysis showed a considerable variation between populations and eco-regions in all studied traits. Variation was relatively higher for reproductive traits (53.2 %) than for vegetative ones (32.8 %). Differentiation between populations (Qst) varied from 0.033 for average length of spikes to 0.56 for heading date with an average of 0.27 which confirm the wide intra-population variation in Tunisian natural populations of B. distachyon. At the DNA level, we show that variation patterns was strongly higher within populations than among populations (98% vs 2%; Fst = 0.021). In addition, almost all characters displayed a significant higher Qst than Fst, indicating occurrence of phenotypic plasticity and local adaptation. The latter is explicable as there is no reason to expect that natural selection would affect in similar fashion all traits and affect all populations at a similar level. We also found a non significant correlation between genetic variation in molecular marker loci and quantitative traits at the multitrait scale (r = 0.016; P = 0.926). This finding attests that the evolution of these two markers in B. distachyon was not paralleled