GENETIC PARAMETERS CONTROLLING SOME MAIZE ADAPTIVE TRAITS TO ELEVATED PLANT DENSITIES COMBINED WITH REDUCED N-RATES

AL-NAGGAR A.M.M.¹, SHABANA R.², ATTA M.M.M.³, AL-KHALIL T.H.^4
1Agronomy Department, Faculty of Agriculture, Cairo University, Giza, Egypt.
²Agronomy Department, Faculty of Agriculture, Cairo University, Giza, Egypt.
³Agronomy Department, Faculty of Agriculture, Cairo University, Giza, Egypt.
⁴Agronomy Department, Faculty of Agriculture, Cairo University, Giza, Egypt.

Received : 25-06-2014     Accepted : 15-07-2014     Published : 03-12-2014
Volume : 3     Issue : 2       Pages : 70 - 82
World Res J Agron 3.2 (2014):70-82

Conflict of Interest : None declared

Low-N stress is one of the factors most frequently occurring under high-plant density. There are common adaptive traits for both high-density (HD) and low-N (LN) stress. Breeding maize for tolerance to high plant density is suggested as an alternative strategy to improve tolerance to low-N. To start an efficient breeding program in Egypt to develop tolerant maize hybrids to high plant density that are able to maximize productivity from land unit area, the present investigation aimed at determining types of gene action and heterosis for somecommon adaptive traits to HD and LN stress. Diallel crosses (except reciprocals) were made among six maize inbreds differing in their adaptive traits of maize to both HD and LN. Nine field experiments were conducted in 2012 and 2013 seasons using a randomized complete blocks design in 3 replications, for each experiment which is one of nine combinations among 3 plant densities [20,000 (LD), 30,000 (medium-density ;MD) and 40,000 (HD) Plants/fed (one fed = 4200 m2) and 3 N-rates (0 (LN ), 120 (MN) and 240 (HN ) kg N/fed ), i.e., 9 environments, namely E1 (HN-LD), E2 (HN-MD), E3 (HN-HD), E4 (MN-LD), E5(MN-MD), E6 (MN-HD), E7 (LN-LD), E8 (LN-MD) and E9 (LN-HD). Under all the 9 environments, the highest average heterobeltiosis was exhibited by percent barren stalks (BS), followed by grain yield/plant (GYPP) and anthesis-silking interval (ASI), while the lowest was observed in days to silking (DTS). In general, E9 (HD-LN) showed the largest number of crosses exhibiting significant favorable heterobeltiosis and the largest average favorable heterobeltiosis for GYPP and harvest index (HI) (49.5 and 20.0%, respectively). The cross L29 × L55 showed the largest heterobeltiosis for GYPP in E6 (133.6%), E3 (133.3%), E5 (132.1%), E2 (132.0%), E4 (131.2%) and E1 (117.0%) followed by L17 × L54 cross (in 6 environments), L 17 × L18 (in 4 environments) L53 × L54, L29 × L54 and L54 × L55 crosses (in 3 environments). The three inbreds L53, L17 and L18 were the best general combiners for GYPP and other studied traits under all 9 environments, while the inbreds L29, L54 and L55 were the worst. The best crosses in specific combining ability effects for GYPP were L29 × L55 in 7 environments (E1 through E7), L17 × L54, L53 × L54 and L17 × L18 crosses in 6 environments (E1 through E6) and L18 × L53 cross in E7, E8 and E9. Performance of a given inbred was an indication of its general combining ability for GYPP, HI and BS in 6 environments (from E1 to E6). The estimates of dominance were much higher, in magnitude, than additive variance for all studied traits under all nine environments. The degree of dominance in all cases was over-dominance. Broad-sense heritability was of medium magnitude (~50 %) for all studied traits under all nine environments. Narrow-sense heritability was generally of small magnitude, but reached about 27% in leaf angle (LANG) under E9. Expected genetic advance from selection in the nine environments was generally of small magnitude, especially under E7 and E9, but was very high for chlorophyll concentration index under E6 and GYPP under E4. ASI, BS and HI of both inbreds and hybrids, ears per plant of inbreds and LANG of hybrids could be considered good selection criteria for tolerance to HD-LN stress combination of genotypes.