The change of yield components' additive variance after recurrent selection of maize (Zea mays L.)

A set of 31 SSD lines from ZP-Syn-1 Co and 37 from ZP-Syn-1 C3 maize populations was studied in this thesis. After selection and seed multiplication in 2000, the trials were carried out in 2001-2002, at Krusevac and Zemun Polje (Serbia, Serbia&Montenegro), in RCB design. After three cycles of recurrent selection we observed a significant decrease of homozygous progenies' means of root and stalk lodged plants percent, plant and ear height, but also of row number per ear. The means of grain number per row and 1000 grain mass were increased, and the differences in ear length and grain yield were not significant. After three cycles, a significant narrowing of additive variance happened for root and stalk lodged plants percent, ear length, and row number per ear, but this narrowing was not significant for the other traits. We have also found significant values of narrow-sense heritability. The significant, positive correlation between grain yield and the most of the investigated traits was found in both selection cycles. We also found a significant negative correlation between some yield components. In both selection cycles were observed high values of the expected genetic gain from direct selection for yield. A possibility of indirect selection for yield through yield components was not established in any investigated cycle. Analysis of path coefficients showed a significant direct effect of ear row number and row grain number on grain yield in the lines of the zero cycle. In the third cycle lines, such an effect was shown by ear height, grain number per row and 1000 grain mass. Indirect effects were not significant. Multiple determination coefficients were significant for the the most of independent variables combinations, in both cycles, calculated by additive correlation coefficients. Cluster analysis showed almost double distances among genotypes and clusters in the zero cycle, and a better cluster definition in the third one. In points out to a narrowing of the total variability after three cycles of recurrent selection. The above mentioned, as well as the fact of the observed decrease of additive variance for three important traits, points to a selection over-pressure to this population. We can suggest that the optimal level of selection intensity in this population could be between 10-15%.