Evaluating the effects of genotype mixture and stress tolerant indices in durum wheat (Triticum durum Desf.) under drought stress

Drought stress is one of the major limitations in crop production worldwide. Genotype mixture has been evaluated as a new way to increase yield in different crops. In this study, different genotype mix systems in durum wheat (Triticum durum Desf.) as impacted by drought stress were investigated. The experiments were conducted under normal and water-stressed conditions in the form of randomized complete block designs, each with three replicates,  in the research farm of the College of Agriculture and Natural Resources of Darab, Shiraz University for two years (2016-2017 and 2017 - 2018). Monocultures of four durum wheat genotypes including Shabrang and Behrang cultivars and DW-92-4, DW-94-14 lines and their binary and quadruple mixing combinations were used in the cropping systems. Drought tolerance indices, including stability tolerance index (STI), mean productivity (MP), geometric mean productivity (GMP), stress susceptibility index (SSI), tolerance index (TOL), yield index (YI), yield stability index (YSI) and a new criterion designated as SIIG (Selection Index of Ideal Genotype) were used and evaluated to identify the best cropping system. Behrang+DW-94-14 cropping system showed the highest GMP, STI and MP values of drought indices, while the highest value (0.890) of SIIG index was identified in the Shabrang+DW-94-14 cropping system. Positive correlations were found among GMP, STI, and MP with YP. Moreover, biplot analysis of these indices using principle component analysis revealed strong positive correlations among GMP, STI and MP while SIIG index was closely related to YSI index. GMP, MP, and STI indices were identified as the best criteria to identify cropping systems in water-stressed conditions. In both normal and water-stressed circumstances, quadruple genotype culture yielded better yields than monoculture and most binary cultures. However, the highest seed yield was obtained in the normal and water-stressed treatments in the Behrang + DW-94-14 cultivation system with an average of 8815 and 7342 kg ha-1, respectively.