Study of combining ability and heterosis of grain yield and yield components in some grain sorghum genotypes under irrigated conditions

The experiments were carried out during 2006/07 and 2007/08 seasons at Elsuki Research Station, Sudan. It constituted 10 cytoplasmic male sterile sorghum lines and nine male fertile sorghum varieties crossed in line x tester analysis resulting in 90 F I sorghum hybrids. The objectives of the experiments were to estimate genetic variability, combining ability and magnitude of heterosis with the ultimate objective of identifying suitable parents for hybrid synthesis .The design of the experiment was a randomized complete block with two replicates. The agronomic traits measured were days to 50% flowering , plant height , stem diameter , head length, head exertion, number of seeds / head, 1000-seed weight and grain yield .The parameters measured included genetic variability ,general combining ability (GCA) , specific combining ability (SCA) ,correlation and heterosis . Significant differences were observed among the parents and crosses for most of the characters studied in both seasons and across them .The general combining ability (GCA) estimates showed that among the lines L 8 (ICSA-38) and L 9 (ICSA-37) were the best general combiners for days to 50 % flowering, plant height ,head length ,head exertion and grain yield, while among the testers T 8 (Ingaz) was the best general combiner for head exertion, 1000-seed weight and grain yield in both seasons and across them .Specific combining ability (SCA) estimates showed that cross L 10 (ICSA-56) X T 4 (EDO-34) had the highest positive and significant values for grain yield in both seasons and across them. The ratio of GCA variance to SCA variance showed that non-additive gene effects were found to be important for the inheritance of days to 50% flowering, plant height, stem diameter, head exertion, number of seeds / head, 1000-seed weigh and grain yield in both seasons and across them .Grain yield was positively correlated with stem diameter, head length, number of seeds I head and 1000-seed weight, while negatively correlated with head exertion, days to 50% flowering and plant height. The following hybrids L8 (ICSA 38) x T4(EDO-34) (6328 kg/ha), L10 (ICSA 56) x T4 (EDO-34) (6293 kg/ha), L3 (KEN-32) X T2 (EDO-15-9-2) (6256 kg/ha) , L9 (ICSA 37) x T1 (EDO-14-1-2) (6243 kg/ha) , L7 (ICSA 41) x T6 (EDO-5-2-25-3) (5765 kg/ha) and Ll (TX623) x T7 (EDOI6 DWF) (5718 kg/ha) showed positive values over mid-parent and heterosis , coupled with positive and significant SCA values for grain yield in both seasons and across them . Moreover, most of these crosses combined high grain yield with medium values of days to 50% flowering, plant height, 1000-seed weight, stem diameter, head exertion, head length and number of seeds per head, suggested that these hybrids could be advanced for testing their yield potential at multilocation trials with the control to confirm their high yield consistency for commercial utilization