Drought is a world-wide spread problem adversely affecting bread wheat production in rainfed agro-ecosystems. Development and identification of efficient selection criteria for developing drought tolerant wheat varieties with stable and high yield potential is of paramount importance. This study was carried out to evaluate 24 indices for selecting the best high yielding and drought tolerant cultivars, among 40 bread wheat genotypes, under four levels of stress intensities: no stress, mild (0.25, 0.35) and severe (0.57). The mean productivity (MP), modified stress tolerance index (MSTIk), superiority index (Pi), mean relative performance (MRP), relative efficiency index (REI), geometric mean productivity (GMP), stress tolerance index (STI), harmonic mean (HARM) and relative decrease in yield (RDY) showed a high power of discrimination among genotypes, and expressed significant correlations with yields under both stress and non-stressed conditions at all stress intensities. This group of indices was capable to select the highest mean yield associated with the least mean variance at 20 % selection pressure. However, as the stress intensity became greater (>35 %), the efficiency of these indices decreased, especially at high stress intensity (57%), where only Pi and MP were still able to target the highest performances. MRP, REI, GMP, RDY and STI can be used interchangeably. Based on GGE analysis, the best performing genotypes were AUS30355, followed by Gladius, Amir-2 and AUS30354 that showed high yield and stability across all the environments. These genotypes are recommended for direct release and/or for use as parents in the breeding programs.

Bread wheat is the major staple food in Morocco. Drought is the most important abiotic stress decreasing yield. Breeding for drought tolerance may be improved by various plant traits. In order to investigate the best selection criteria to develop drought tolerant varieties, 40 bread wheat genotypes were evaluated under two locations representing the stressed and non-stressed environments, using randomized complete block design with three replications during the cropping season 2014. Under stressed conditions, analysis of variance exhibited significant differences among grain yield, thousand kernel weight, number of plants, number of spikes and tillers per plant, plant height, plant vigor, chlorophyll content and canopy temperature; and non-significant differences for biomass, harvest index, number of days to heading and flowering, and chlorophyll fluorescence. According to correlation and principal component analysis, the grain yield was positively related with biomass, thousand grain weight, number of fertile spikes and plant vigor; and indirectly associated positively with harvest index, plant height and negatively with number of days to flowering, canopy temperature and chlorophyll content. Those traits, correlated to grain yield under stress, can be used as indirect selection for drought tolerance to obtain higher yield potential in dryland conditions. Moreover, thousand grain weight in non-stressed conditions was positively correlated to biomass, number of fertile spikes and its homologue in stressed conditions. Also, the biomass in favorable conditions was correlated to thousand grain weight and harvest index in mild stressed conditions. Thus, those two traits may be used to improve performance in drought prone environments.

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.

The present study aims to compare two different methods for the determination of soil organic matter (SOM); the wet acidified dichromate oxidation methods Walkley-Black (WB) and the combustion's one (mass loss on ignition -LOI); in order to find out the best one in terms of suitability, environmentally-friendly, time-efficiency and economical benefit. Forty-five Moroccan soil samples (El Guich, Koudia and Merchouche area) from 0-20 cm depth with different classes, textures and organic matter contents were evaluated. According to the results, a strong linear relationship was observed between LOI-OM and WB-OM methods for all the sites. However, El Guich and Koudia recorded much larger regression coefficients (0.745 *** and 0.611 *** respectively) compared to Merchouche site (0.452 ** ). Therefore, the SOM by walkley-Black method can be easily calculated from the LOI method at 500±25 ºC for 2 hours using linear equation in order to minimize the analysis time and consumption of chemicals for routine laboratory. In addition, it was noticed that the SOM contents calculated by the LOI method are higher in Merchouche soils compared to that of WB due to the presence of a large amount of clay minerals in the Merchouche soils (43.9 < %clay < 56.1) in comparison with those of El Guich (5 < %clay < 7.5) and Koudia (16.1 < %clay < 20.4). This study revealed that both methods were reliable but W.B method was more accurate and suitable for calcareous soils and those with high clay contents. However, LOI method is an accurate and beneficial for non-calcareous soils with low clay content.