COMBINING ABILITY AND HETEROSIS FOR MAIZE GRAIN YIELD AND SOME AGRONOMIC CHARACTERS

The present study was carried out at the Experimental Station Farm, Faculty of Agriculture, Mansoura University, Dakahlya Governorate, during the two successive seasons of 2011 and 2012 to determine general, specific combining abilities and heterosis for grain yield and yield associated traits by crossing 6 inbred lines of maize in a half diallel mating design. Fifteen F1 single crosses with their parents were planted in a randomized complete block design with three replicates. Results showed that mean squares of crosses were significant for all studied traits i.e. number of days to 50% tasseling and silking, plant height, number of rows/ear, number of grains/row, 100-grain weight, grain yield/plant and shelling percentage. The analysis of variance revealed highly significant mean squares of general combining ability (GCA) and specific combing ability (SCA) for all studied traits, indicating the importance of both additive and non additive genetic effects for these traits. GCA/SCA variances ratios were found to be greater than unity for number of days to 50% tasseling and silking, plant height and 100-grain weight, indicating that the additive and additive×additive types of gene action were greater importance in the inheritance of these 4 traits. Best GCA effects for earliness traits (number of days to 50% tasseling and silking) achieved inbred lines P4 (Inb.173) and P5 (Inb.174), for plant height were P1 (Sd63), P3 (Inb.19), P4 (Inb.173) and P5 (Inb.174), for number of rows/ear were P1 (Sd63), P3 (Inb.19) and P4 (Inb.173), for 100-grain weight was P1 (Sd63). Inbred lines P1 (Sd63) and P2 (Sd7) showed best GCA effects for grain yield. Also P2 (Sd7) and P6 (Inb.170) showed best GCA effects for shelling percentage. Hybrid combinations P2×P5 and P3×P6 showed largest SCA effects for number of days to 50% tasseling, for number of days to 50% silking were P1×P2, P1×P6, P2×P5 and P3×P4, for plant height were P1×P3, P1×P5, P2×P3, P2×P6, P4×P5 and P4×P6, for number of rows/ear were P1×P2, P1×P4, P2×P3, P3×P4, P4×P5 and P5×P6 and for shelling percentage were P1×P3, P1×P4, P2×P3, P2×P4, P3×P4 and P5×P6. Concerning number of grains/row, grain yield/plant and100-grain weight, most of crosses recorded positive significant or highly significant SCA effects. Results showed significant or highly significant heterosis for all studied traits. Cross P3×P6 was the best, with highly significant negative heterosis over mid and better parents for number of days to 50% tasseling. Cross P2×P3 recorded the highest negative heterosis over mid and better parents for number of days to 50% silking. Regarding to plant height, none of the cross combinations showed negative heterosis over mid and better parents. The best cross over mid and better parents for number of grains/row, grain yield and 100-grain weight was P1×P2. Crosses P1×P4 and P5×P6 recorded the highest positive heterosis over mid and better parents for number of rows/ear and shelling percentage, respectively. Therefore, it could be stated that parents with good positive GCA for grain yield (P1 and P2), negative GCA for tasseling, silking date (P4 and P5) and dwarf plant height (P1, P3, P4 and P5) may be extensively used in hybridization program as a donor. The better performing four crosses (P1×P2, P1×P4, P1×P6 and P2×P3) can be utilized for developing high yielding hybrid varieties as well as for exploiting hybrid vigor.