Genetic improvement of Grain Yield by Determination of Selection Index in Single Cross Hybrids of Maize (Zea mays L.)

Selection based on proper selection indices can be one of the most effective methods for indirect selection of yield and yield components, simultaneously. In order to determination of selection index for improvement of maize yield, 60 single cross maize hybrids were planted in two separate experiments (drought stress and normal conditions) based on randomized complete block design (RCBD) with three replications in Torogh agricultural station of Khorasan Razavi agricultural and natural resources research and education center, Mashad, Iran in 2013-2014. Morphological and phenological traits, yield and yield components were recorded. Selection indices were calculated based on results of stepwise regression considering to phenotypc, genotypic and economic values. Based on stepwise regression results in normal condition, physiological maturity, plant height, kernel depth, kernel no./row and tassel length totally could explain 60.68 percent of gain yield variation, then these traits were used to calculate selection index. In drought stress condition, kernel no./row, plant height, ear height, 1000 kernel weight, ear length and leaves no. above ear could explain 63.77 percent of grain yield variation that these traits were used to calculate of selection index. We used 5 optimum selection indices (smith-hazel) and one basic selection index as Pesk-Baker to screen the maize genotypes. The results showed that the relative efficiency of selection index based on yield and expected genetic gain for all of measured traits in selection index 2 was higher than others in both normal and drought stress conditions. Based on grain yield and selection indices, 20 percent of the best genotypes were selected by each selection indices. Based on derived results in normal condition, genotype no. 60 (ksc704 commercial hybrid) were selected by all of  selection indices as the best genotype, but in drought stress condition, different genotypes were selected by different selection indices like genotypes 16 (ME77006/1×K1263/1), 22 (ME77006/1×K1263/1) and  34 (ME78005/2× A679), that these genotypes at least were selected by 2 or 3 selection indices.