Direct and indirect selection for drought tolerance in alien tetraploid wheat x durum wheat crosses

Abstract

After the evaluation of numerous accessions of primitive wheals for yield components and morphophysiological traits related to drought tolerance (e.g., maintenance of high relative water content, RWC; photochemical quenching of chlorophyll fluorescence, qQ; and chlorophyll loss, chi, under moisture stress conditions), several accessions belonging to three species (Triticum dicoccum, T. polonicum, and T. carthlicum) were crossed with the improved durum wheat varieties Cham 1 and Om Rabi 5. A direct selection (F(2) progeny) for yield and an indirect physiological trait were applied on interspecific T. durum x T. dicoccum, T. durum x T. polonicum, and T. durum x T. carthlicum populations. Divergent selection was applied to validate the possible use of morphophysiological traits (root parameters, RWC, photochemical quenching, proline content, and carbon isotope discrimination) in selection, and to evaluate the resulting effects on yield. Heritability and selection response of these traits has been evaluated, and the impact of divergent selection for morphological and agronomic characters was studied under field conditions. The divergent populations were evaluated under different environmental conditions in France, Syria, and Yemen. Selection for morphophysiological traits related to moisture stress, such as root parameters, RWC and carbon isotope discrimination was possible due to high h(2) values and effective, resulting in high genetic gains. However, the effect of selection for these traits on yield stability needs to be further studied. Furthermore, a modified bulk method (F(2) 'progeny method') was developed. Direct selection for grain yield per plant in F(2) was carried out and yield per line in F(3) was evaluated under contrasting environmental conditions in France, Syria, and Tunisia. Results revealed that some F(3) lines were higher yielding than the improved durum wheat varieties Cham 1 and Om Rabi 5 under both stressed (Aleppo) and favourable (Montpellier) environmental conditions. Lines were evaluated in preliminary yield trials at Montpellier (France), Aleppo (Syria), and Constantine (Algeria). Results indicated that the use of related species combined with the use of the modified bulk breeding method is promising not only for increasing durum wheat yield in drought prone environments, but also for improving durum wheat yield stability across contrasting environments. Results of both breeding strategies are presented, and the potential advantages of using related tetraploid species in durum wheat breeding for drought tolerance are discussed.