Evaluation of Drought Tolerance in Bread Wheat Genotypes using new mixed method

Introduction Selection index of ideal genotype (SIIG) technique, proposed in this paper, is one that is very simple and easy to implement. According to this technique, the best genotype would be the one that has the least deviation from the positive ideal parameter and the most deviation from the negative ideal parameter. The positive ideal parameter is a parameter with maximizes drought tolerance and minimizes drought tolerance, whereas the negative ideal parameter is a parameter with stress susceptibility. In fact, SIIG technique is derived from technique for order preference by similarity to ideal solution (TOPSIS) method (Hwang and Yoon, 1981). If for selection of drought tolerance genotypes, researchers can be used several methods simultaneously, presumably will increase the efficiency of selection (Zali, et al., 2015). SIIG technique that was proposed in this paper is a method that can select drought tolerance genotypes using different procedures.   Materials and methods 20 genotypes were tested in randomized complete block design with three replications at the experimental farm of Faculty of Agriculture, Razi University of Kermanshah, Iran in 2014-2015. The SIIG technique is composed of the following steps: Step 1: Construct normalized selection matrix: The normalization of the decision matrix was done using the following transformation for each rij. r= x ∑ x i=1,…,n; j=1,…,m. Where rij is the normalized stability methods or different trait value. D=x x x x x x⋮ ⋮x x x →R =r r r r r r⋮ ⋮r r r Step 2: Determine the positive ideal parameter (maximum stability) and negative ideal parameter (minimum stability) genotypes: The positive ideal and negative ideal parameters are determined, respectively, as follows: A={r,r,…,r} A= maxrj∈Ω ,minr|j∈jΩ Where Ω is the set of maximum stability and Ω is the set of minimum instability. A={r,r,…,r} A= minrj∈Ω ,maxr|j∈jΩ Where Ω is the set of minimum stability and Ω is the set of maximum instability. Step 3: Calculate the segregation measures for each genotype: The two Euclidean distances for each genotype were calculated. The separation of each stability value from the positive ideal parameter is given as: d= (r−r) i=1,…,n Similarly, the separation from the negative ideal parameter is given as: d= (r−r) i=1,…,n Step 4: Calculate the relative closeness to the ideal parameter: The relative closeness (for selection stable genotypes) to the ideal parameters can be defined as: SIIG= d d+d i=1,2…,m, 0≤SIIG≤1.     Results and discussion Twelve drought tolerance indices includingmodified stress tolerance index(MSTI), yield stability index(YSI), yield index(YI), stress susceptibility index(SSI), stress tolerance index(STI), tolerance index(TOL), geometric meanproductivity(GMP),harmonic mean(HAM), mean productivity(MP), drought resistance index(DI), relative drought index(RDI) and also selection index of ideal genotype were calculated. Using these indicators and priniciple component analysis genotypes 1, 12 and 15 were selected as tolerant genotypes. It is also 1, 12 and 15 genotypes with the highest selection index of ideal genotype values, near to one was accepted drought tolerance genotype, also 4 genotype with the lowest selection index of ideal genotype value, near to zero was accepted drought susceptible. The results were the same in different ways. Modified stress tolerance index, harmonic mean, mean productivity, stress tolerance index and geometric meanproductivity the harmonic mean and K1STI significant positive correlation with yield in stress and non-stress conditions were therefore the best indices to identify superior genotype. Conclusion The selection index of ideal genotype (SIIG) is a selective model and is used to select the most suitable genotype among genotypes in different environments. Using the SIIG method, drought tolerance indexes, different stability parameters or different traits can be determined as a single index, and the selection of superior genotypes is made more reliable and accurate.