EFFICIENCY OF LATE AND EARLY SELECTION FOR GRAIN YIELD UNDER DIFFERENT SELECTION CRITERIA AND DNA MARKER POLYMORPHISM IN WHEAT (Triticum aestivum L.)

Two cycles of early selection (F4 & F5) and one cycle of late direct selection (F5) were used for grain yield to study the efficiency of pedigree line selection for grain yield in a population (multi-cross) of wheat at the Experimental Farm of Assiut University, Egypt.  Early selection was carried out under different selection criteria.  The results revealed high significant differences among F3 families for all studied traits, reflecting the genetic variability among obtained families of base population. The genotypic coefficient of variation was decreased from the base population due to the increasing of homogeneity among families after selection from cycle to another.  It decreased from 28.86 % in the base population to 15.82 and 3.08 % in grain yield/plant (as a selection criteria) after second cycle of early selection and late selection, respectively. The response to selection in grain yield was 25.51 % in late selection compared to 17.76 %, 2.44, 16.80 and 12.49 % with grain yield/plant, biological yield/plant, number of spikes/plant and harvest index as selection criteria in early selection, respectively, after second cycle of selection.  It is clear from these results that the late selection gave the highest values of selection response (25.51) followed by early selection (17.76 %) for grain yield/plant as selection criteria. The high positive coefficient of genotypic correlation between grain yield/plant and each of number of spike/plant, biological yield and harvest index in base population is still in the same direction after second cycle of selection under different selection criteria, consequently, these traits could be used as selection criteria next to direct selection to improve grain yield in wheat. Late direct selection matched early direct one for grain yield/plant and indirect for number of spikes/plant for only the highest family (No. 100) among selections which yielded 21.81 g for grain yield/plant. Results of EST marker indicated that the obtained lines have wide range of genetic variation as revealed by the molecular DNA marker level.