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Abstract SUMMARY A study on divergent maize populations was carried out for the following objectives: 1. To determine the relative importance of GCA and SCA for yield and other agronomic traits. 2. Estimating the magnitude of heterosis in the crosses developed among some of divergent populations. 3. To determine if any of the parental populations might be used as ~ ~ or developing good performing inbred lines to be used in a hybrid program. 4. To determine the magnitude of interaction with different planting dates. Ten populations are used in this study. Three of them are locals obtained by Agricultural Research Center, Egypt, namely, AED, Giza 2 and Sids 7734. The other seven exotic populations were provided by International Maize and Wheat Center (CIMMYT, Mexico), namely Pool 16, Pool 20, Pool 31, Pop 21, Pop 32, Pop 43 and Tuxpeno PB C • 17 They were crossed to obtain F1’s set in 1985 season. Parents and their forty five F1 hybrids were tested at two different planting dates in 1986 at the Experimental Research Station of Pioneer Overseas Corporation at Toukh District, Kalubia Governorate. - 80 - A randomized complete block design (RCBD) with four replicatlons was used for both planting dates. Analyses of variance was computed seperately for the two different planting dates as well as their combined. Analyses for combining ability was carried out using Griffing’s 1956 method II model \ I. Heterosis was computed only for combined analysis as percentage deviation of F I mean performance from its best parent value. Data were recorded on the following attributes: Grain yield (Kgs!plot), late wilt disease, days to 50 % pollen shedding and silking, plant height, ear height, prolificacy, weight of 100 Kernels, ear length, number of kernels per row, ear diameter and number of rows per ear. Results showed that: 1. Performance of genotypes including parents and crosses were not similar in their behaviour in both planting dates as indicated by the significance of genotypes x planting dates for yield and other agronomic traits. This might be taken up as a fact to ernphasize the breeder to do his selection and breeding nurseries at the time of crop growing season. 2. Genotypes mean squares reached the significant level of probability for all traits in both planting dates as well as the combined analysis. Significant interactions between genotypes and planting dates were detected for all traits with the exceptions of number of rows per ear, ear length and number of kernels per row. - 81 - 3. Appreciable parents mean squares were obtained for all traits. Also significant interactions between parent and planting dates were detected for all traits except ear length and number of kernels per row. 4. Hybrids mean squares were found herein to reach the significant level in all cases. Significant interactions between FI crosses and planting dates were detected for all traits except ear diameter, number of rows per ear, ear length and number of kernels per row. 5. Significant heterosis was obtained for all traits with the exception of late wilt, ear height in both planting dates and the combined analysis, plant height and number of rows per ear in late planting and the combined data and prolificacy and IOO-kernel weight in late planting date. Significant interactions between parents YS crosses and planting dates were reached for all traits with . the exceptions of late wilt disease, plant height, ear height, ear length and number of kernels per row. 6. General combining ability (GCA) mean squares reached the significant level of probability for all traits. Significance of specific combining ability (SCA) mean squares were detected for all traits except number of kernels per row in both planting dates and the combined analysis, and number of rows per ear in late planting. The higher GCA to SCA ratios which exceeded more than the unity were detected for all traits, indicating that the additive - 82 - and additive by additive gene actions were the large contributions of total genetic var iabili ty, 7. The interactions between planting dates and both of GCA and SCA mean squares reached the significant level of probability for all the studied attributes, with the exception of number of rows per ear, ear length and number of kernels per row. Also SCA x planting date mean square was not detected for ear diameter. As could be seen from the higher ratios of GCA x planting dates to SCA x planting dates which exceeded the unity, it is clear that additive gene effects were more biased by the interaction with environments than non-additive effects. 8. The best combiner parents were G. 2, Sids 7734, Pool 20 and Pool 31 for earliness, Pop 21, Pop 32 and Pop 43 for late wilt disease resistance, Pool 31 and Tuxpeno PBC.-17 for plant height and ear placement reduction, AED, G. 2, Sids 7734, Pool 20 and Pop 32 and Pop 43 for prolificacy, G. 2, Sids 7734, Pop 32 and Pop 43 for weight of 100 kernels, AED and G. 2 for ear length, AED and Sids 7734 for ear diameter, AED, Pool 31 and Pop 32 for number of rows per ear, AED, G. 2 and Pop 43 for number of kernels per row, and AED, G. 2, Sids 7734 and Pop 43 for grain yield. 9. The F1 hybrids namely (AED x Pop 21), (AED x Pop 43), (AED x Tuxpeno PBOft17), (Pool 16 x Pop 43), (Pool 31 x Pop 32), (Pool 31 x Pop 43) and (Pop 43 x Tuxpeno PBC.-1?) appeared to be - 83 - the most promising for breeding towards high yielding potentiality, the f I crosses namely (AED x Pool 31), (G. 2 x Pop 43) and (Pop 32 x Tuxpeno PBcool7) would be promising as a source of late wilt resistance, the F 1 hybrids namely, (5ids 7734 x Pop 32), (Pool 31 x Pop 32), (Pool 31 x Tuxpeno PBC*l7l. and (Pop 43 x Tuxpeno PBC~ 17) showed the tendency towards earliness of relative maturity, (AED x G. 2) and (Pop 21 x Tuxpeno PBC,- 17), achieved the shortest heights and lowest car placements. The prolific hybrids were (AED x Pop 43), (AED x Tuxpeno PBCA17), (Pool 16 x Pool 20), (Pop 32 x Tuxpen o PBC. 17), (Sids 7734 x Pop 32) and (Pool 16 x tuxpeno PBC,d 7). Thereupon, the study recommend that: the parental varieties, AED, G. 2. Sids 7734 and Pop 43 exhibited the highest positive performances among all populations under study for yield, prolifiC trait, weight of 100 kernels. ear length except for AED. ear diameter and ear length achieved by AED and G. 2. The F I hybrids. namely, (AED x Pop 21), (AED x Pop 43), (AED x Tuxpeno PBC 17), (Pool 16 x Pop 43), (Pool 31 x Pop 32), (Pool 31 x Pop 43) and (Pop 43 x Tuxpeno PBC”I71, also, showed good yield potentiality and positive trends for other agronomic traits. |