[The Importance of Indirect Selection for Genetic Improvement of Some Quantitative and Qualitative Traits in Maize (Zea mays L.)]

The study was carried out at Maize Researches Department, General Commission for Scientific Agriculture Researches (G.C.S.A.R.) Damascus, Syria. During the summer growing seasons of 2010, 2011 and 2012. The seeds of the six populations (P1, P2, F1, F2, BC1 and BC2) for the four hybrids (IL.766-06 × IL.792-06), (IL.292-06 × IL.565-06), (IL.459-06 × IL.362-06) and (IL.459-06 × IL.292-06) were produced at 2010 and 2011 growing seasons. The six populations of each hybrid were evaluated at two planting dates, 12/5 early one and 12/6 late one, in a Randomized Complete Blocks Design with three replications, to study the potence ratio, mid and better parents heterosis, inbreeding depression, phenotypic and genotypic coefficient of variation, heritability, genetic advance, gene action, phenotypic correlation and path coefficient analysis for grain yield per plant and its components and some morphological and quality traits. Results could be summarized as follows: 1. Potence ratio values exceeded the unity in most of the studied traits in the four crosses at two planting dates. Over dominance towards the higher parent was detected for most studied traits. Generally, potence values followed the same trend as heterotic effects for all traits. The results showed highly significant positive heterosis relative to mid and better parent for most studied traits in the four crosses. 2. Values of inbreeding depression were positive for all studied traits in the four crosses at two planting dates, except for days to 50% silking. 3. The phenotypic variations were greater than genotypic variations for all studied traits in the four crosses at tow planting dates, indicating greater influence of environment in the expression of these traits. 4. Narrow sense heritability and genetic advance were low and moderate in most of the studied traits due to the dominance of non-additive gene action in controlling the genetic variation of the most studied traits and this predict low to medium values of genetic advance through selection process, and the importance of the selection to improve these traits in the medium or late segregation generation. 5. The inheritance of all the studied traits was controlled by additive and non-additive genetic effects, but dominance gene effects play the major role in controlling the genetic variation of the most studied traits. Suggesting that the improvement of those characters need intensive selection through later generations. 6. Most of the values of the genetic parameters were higher in the early planting dates than those in the late one. Indicating that the early planting date can consider a suitably environment to do the selection for the most of the studied traits. 7. Correlation coefficients among traits indicated that grain yield per plant was positively and significantly associated with ear length, number of rows per ear, number of kernels per row and 100 kernel weight, at the two planting dates. 8. The path coefficient results showed that each of ear length, number of rows per ear, number of kernels per row and 100 kernel weight can be considered as the most important sources of plant grain yield variation under normal and late planting dates.