Six advance wheat lines (B4N11, B6N5, B6N12, BRF1, BRF3 and BRF17) were crossed with four highly adapted cultivars (Zam-04 (ZM04), Kohat-10 (KT10), Pirsabak-08 (PS08) and Janbaz (JZ)) in line × tester fashion during 2011-12 to develop 24 F1 hybrids. The resultant hybrids along with parents were evaluated during 2012-13 at Cereal Crops Research Institute (CCRI), Pirsabak, Nowshera, Pakistan as independent experiments under irrigated and rainfed environment using randomized complete block design with three replications. General and specific combining ability, best-parent heterosis, heritability and selection response for maturity, yield and its component traits were determined under each environment. Genotype × environment effects were highly significant for all traits except spike length. Parents vs. F1 hybrids contrast was significant for almost all traits under each test environment. Similarly, differences among wheat lines, testers and line × tester interaction effects spikelets spike-1 under rainfed environment. 2 2sca and their ratio 2gca/ 2 2 2gca for all traits except for days to maturity, grains spike-1 and grain filling duration, indicating predominantly non-additive gene action under irrigated as well as rainfed environment. There was general reduction in mean performance of parental genotypes as well as F1 hybrids for all traits under rainfed environment. F1 hybrids were about 4 to 6 days earlier in heading, anthesis and maturity than parental genotypes both under irrigated and rainfed production environments. BRF1, BRF3, BRF17, ZM04, PS08 and JZ were six best parental genotypes with more spikes plant-1 under irrigated, while BRF3, BRF17, ZM04, PS08 and JZ had higher spikes plant-1 under rainfed environment. Similarly, five F1 hybrids with more spikes plant-1 were B6N5 × ZM04, B6N5 × JZ, BRF1 × ZM04, BRF1 × KT10 and BRF17 × ZM04 under irrigated and B6N5 × ZM04, B6N5 × JZ, B6N12 × JZ, BRF3 × KT10, BRF3 × PS08 and BRF3 × JZ under rainfed environment. Four top ranking F1 hybrids for grains spike-1 were B4N11 × PS08, B4N11 × JZ, BRF1 × JZ and BRF17 × JZ under irrigated, while B4N11 × KT10, B6N5 × ZM04, BRF1 × KT10 and BRF17 × ZM04 under rainfed environment. Top three parental genotypes with highest 1000-grain weight under irrigated environment were B6N12, ZM04 and JZ, while ZM04, KT10 and JZ under rainfed environment. Similarly, top four F1 hybrids with more 1000-grain weight were B4N11 × ZM04, B6N5 × KT10, BRF3 × KT10 and BRF17 × KT10 under irrigated, while B4N11 × JZ, B6N5 × KT10, B6N12 × JZ and BRF1× PS08 under rainfed environment. High yielding parental genotypes were BRF3, B4N11, KT10 and JZ, whereas high yielding hybrids were BRF1 × ZM04 and B4N11 × KT10 under irrigated environment. However under rainfed environment, best yielding parental lines were BRF1 and JZ while BRF3 × PS08 and B6N5 × ZM04 were high yielding F1 hybrids. Averaged over the two test environments, BRF3 among parents, while B6N5 × ZM04 and BRF1 × ZM04 among F1 hybrids were top ranking genotypes by producing more tillers plant-1, spikes plant-1, spike length, grain yield and biological yield. Generally, F1 hybrids showed greater yield potential than their parental genotypes under each test environment. Among lines, B4N11 was good general combiner for most traits like days to heading, anthesis, maturity, flag leaf area and plant height, whereas among testers ZM04 was best general combiner for days to heading, anthesis, tillers plant -1, spikes plant-1 and grain yield plant-1 both under irrigated as well as rainfed environment. However, F1 hybrids B6N5 × JZ, BRF1 × ZM04, BRF3 × PS08 and BRF17 × PS08 were best specific combiners for early maturity under irrigated environment, while B6N5 × PS08 and BRF17 × JZ were good specific combiners under rainfed environment. F1 hybrids B4N11 × KT10, B6N5 × JZ, BRF1 × PS08 and BRF1 × JZ were good specific combiners for plant height, while BRF3 × PS08 was good specific combiner for 1000-grain weight under both environments. F1 hybrid B6N5 × ZM04 was best specific combiner for tillers plant-1, spikes plant-1, spike length, grains spike-1 and biological yield plant-1 both under irrigated and rainfed environments. Likewise, F1 hybrids B4N11 × PS08, BRF1 × ZM04 and BRF1 × KT10 were best specific combiners for grain yield plant-1 both under irrigated as well as rainfed environment. The contribution of line × tester interaction was generally more to total variation in most traits as compared to either lines or testers, ranging from 27.1 to 63.2% and 25.6 to 51.8% under irrigated and rainfed environment, respectively. Similarly, five F1 hybrids BRF1 × ZM04, BRF1 × PS08, BRF3 × ZM04, BRF17 × ZM04 and BRF17 × PS08 expressed significantly positive best parent heterosis for tillers plant-1 and spikelets spike-1, while BRF1 × PS08 for 1000-grain weight under both environments. Eight F1 hybrids viz. B4N11 × ZM04, B4N11 × KT10, B4N11 × PS08, BRF1 × KT10, BRF3 × ZM04, BRF3 × KT10, BRF3 × PS08 and BRF17 × ZM04 had significantly positive best-parent heterosis for grain yield plant-1 under irrigated as well as rainfed environment. Genetic variances were greater in magnitude than environmental variances for most traits both under irrigated and rainfed environment. High broad-sense heritability estimates were observed for most traits under both environments. Days to heading, maturity, grain filling duration, spike density and grain yield plant-1 had moderate narrow-sense heritability under irrigated as well as rainfed environment. However, important yield like tillers plant-1, spikes plant-1, spike length, spikelets spike-1, 1000- grain weight, biological yield and harvest index had low narrow-sense heritability under one or both of the test environments. Expected selection responses were generally greater in magnitude under irrigated than rainfed environment for important yield contributing traits like grains spike-1, 1000-grain weight, biological yield, grain yield and harvest index. Changes in direction and magnitude of mean performance, combining ability, heterosis and heritabilities were observed under irrigated vs. rainfed environments, indicating significant role of environment on gene expression. Simultaneous evaluation of new wheat populations followed by selection under each test environment will be more effective for development of new wheat cultivars with optimum performance under irrigated as well as rainfed environment.