Drought-Tolerance QTLs Associated with Grain Yield and Related Traits in Spring Bread Wheat

The present research aims to identify the efficient combination of drought-tolerance selection criteria and associated quantitative trait loci. A panel of 197 bread wheat genotypes was evaluated for yield- and drought-tolerance-related traits in two environments (favorable and semiarid) for 2 years (2015-2016). Grain number, biomass, number of fertile spikes per plant and ground cover exhibited a significant correlation with grain yield and constitute potential secondary selection criteria for yield under drought conditions. About 73 significant marker-trait associations were detected along various chromosomal positions. The markers "wsnp_Ex_Rep_c67786_66472676" and "ExcalibuR_c24593_1217" exhibited important genetic gains associated with yield increase under drought (11 and 7%, respectively). The markers "KukRi_c94792_127" and "wsnp_Ex_c298_580660" showed a significant correlation with grain yield, biomass and grain number and were associated with a significant increase in yield performance at the semiarid site (+6 and +7%, respectively). The ground cover was found associated with grain yield and biomass through the markers "wsnp_Ex_Rep_c67786_66472676" (+11%) and "KukRi_c49927_151" (+10%). One marker "TduRuM_contig25432_1377" on chromosome 5B at 20 cM was consistently correlated with the number of fertile spikes across both environments. Further research should be considered to validate the efficiency of these markers to undertake selection for drought tolerance under various environments and genetic backgrounds.

Towards a comprehensive characterization of durum wheat landraces in Moroccan traditional agrosystems: analysing genetic diversity in the light of geography, farmers' taxonomy and tetraploid wheat domestication history

BACKGROUND

Crop diversity managed by smallholder farmers in traditional agrosystems is the outcome of historical and current processes interacting at various spatial scales, and influenced by factors such as farming practices and environmental pressures. Only recently have studies started to consider the complexity of these processes instead of simply describing diversity for breeding purposes. A first step in that aim is to add multiple references to the collection of genetic data, including the farmers' varietal taxonomy and practices and the historical background of the crop.

RESULTS

On the basis of interview data collected in a previous study, we sampled 166 populations of durum wheat varieties in two traditional Moroccan agrosystems, in the Pre-Rif and Atlas Mountains regions. Using a common garden experiment, we detected a high phenotypic variability on traits indicative of taxonomical position and breeding status, namely spike shape and plant height. Populations often combined modern (short) with traditional-like (tall) statures, and classical durum squared spike shape (5 flowers/spikelet) with flat spike shape (3 flowers/ spikelet) representative of primitive domesticated tetraploid wheat (ssp. dicoccum). By contrast, the genetic diversity assessed using 14 microsatellite markers was relatively limited. When compared to the genetic diversity found in a large collection of tetraploid wheat, it corresponded to free-threshing tetraploid wheat. Within Morocco, the two studied regions differed for both genetic diversity and variety names. Within regions, neither geography nor variety names nor even breeding status constituted strong barriers to gene exchange despite a few significant patterns.

CONCLUSIONS

This first assessment of morphological and genetic diversity allowed pointing out some important factors that may have influenced the structure and evolutionary dynamics of durum wheat in Morocco: the significance of variety names, the occurrence of mixtures within populations, the relative strength of seed exchange between farmers and local adaptation, as well as the fate of modern varieties once they have been introduced. Further, multidisciplinary studies at different spatial scales are needed to better understand these complex agrosystems of invaluable importance for food security.

Anchoring durum wheat diversity in the reality of traditional agricultural systems: varieties, seed management, and farmers' perception in two Moroccan regions

BACKGROUND

Traditional agrosystems are the places were crop species have evolved and continue to evolve under a combination of human and environmental pressures. A better knowledge of the mechanisms underlying the dynamics of crop diversity in these agrosystems is crucial to sustain food security and farmers' self-reliance. It requires as a first step, anchoring a description of the available diversity in its geographical, environmental, cultural and socio-economic context.

METHODS

We conducted interviews with farmers cultivating durum wheat in two contrasted traditional agrosystems of Morocco in the Pre-Rif (163 farmers) and in the oases of the Atlas Mountains (110 farmers). We documented the varietal diversity of durum wheat, the main characteristics of the farms, the farming and seed management practices applied to durum wheat, and the farmers' perception of their varieties.

RESULTS

As expected in traditional agrosystems, farmers largely practiced diversified subsistence agriculture on small plots and relied on on-farm seed production or informal seed exchange networks. Heterogeneity nevertheless prevailed on many variables, especially on the modernization of practices in the Pre-Rif region. Fourteen (resp. 11) traditional and 5 (resp. 3) modern varieties were identified in the Pre-Rif region (resp. in the Atlas Mountains). The majority of farmers grew a single variety, and most traditional varieties were distributed in restricted geographical areas. At the farm level, more than half of the varieties were renewed in the last decade in the Pre-Rif, a more rapid renewal than in the Atlas Mountain. Modern varieties were more prevalent in the Pre-Rif region and were integrated in the traditional practices of seed production, selection and exchange. They were clearly distinguished by the farmers from the landraces, the last ones being appreciated for their quality traits.

CONCLUSIONS

The surveyed traditional agrosystems constitute open, dynamic and heterogeneous entities. We suggest that competing factors could favour or limit the cultivation of improved varieties and the erosion of original durum wheat diversity. This first description opens the way to focused further investigations, including complementing variety names with cultural, genetic and phenotypic information and unravelling the multidimensional factors and consequences of modern variety adoption.

Organisation de la variabilité enzymatique des populations marocaines de luzerne (Medicago sativa L.): structures géniques et génotypiques

Five enzymatic loci have been analyzed electrophoretically to study the genic and genotypic structures of 20 populations of alfalfa (Medicago sativa L.) from Morocco. Five different geographical origins were considered: Ziz, Drâa and Dadès (three oases in the Sahara), Demnate, and oases from mountainous regions. For comparison, three cultivars (African, Moapa, Europe) and four populations (one from Sudan, two from Spain, and one from Provence) of foreign origin were included in the study. The genic structures of the above 27 populations or cultivars allowed a good discrimination among populations and origins. The alleles with low frequency played a significant role in the discrimination and the discrimination was better when established on the basis of allelic diversity than on genotypic structures. The Flemish cultivar Europe differed from all other mediterranean material (African, Moapa, Provence, Morocco populations) but closely resembled two Spanish ecotypes from Mielga. The cultivars African and Moapa proved to be different from the Morocco populations. The latter could be divided into two different genic pools: one consisted of the Demnate populations, the other grouped populations of the Sahara and mountainous oases with no clear distinction between geographical origins. Genotypic structures based on the analyses of 30 plants from each population or cultivar did not allow to discriminate among populations. To study fixation indices and verify the panmictic equilibrium hypothesis, the number of specimen per population or cultivar had to be increased for a few populations. All the populations or cultivars analyzed showed a lack of heterozygous plants and the hypothesis of a Hardy–Weinberg equilibrium could not be accepted. Frequencies of monogenic individuals and digenic duplexes were high, but tetragenic individuals were infrequent.Key words: alfalfa, isozymes, genic structures, genotypic structures, infrequent alleles.[Journal translation]