The aim of this study was to isolate superior inbred lines and better combining parents for suitable hybrids and to determine percent of heterosis using standard commercial checks in a 7 × 7 diallel analysis excluding reciprocals over five environments. The mean sum of square obtained from combined analysis of variance showed the presence of genetic variability among the crosses, environment and crosses × environment interaction for all of the characters under study. The variances for general combining ability (GCA) and specific combining ability (SCA) of variance were found significant for all the characters. However, relative magnitude of variances indicated that additive gene effects were more prominent for all the characters studied. GCA and SCA effects both showed significant interaction with environment for all the traits. This clearly suggested the need of selecting different parental lines for hybrids for different ecological situations. Parents P3, P5 and P6 were the best general combiner for high yield; parents P6 for earliness; and P1, P2 and P3 for dwarf plant type. The range of heterosis expressed by different crosses was from -13.04 to 5.25 % percent for grain yield. The better performing six crosses (P1 × P2, P1 × P5, P3 × P4, P3 × P6, P3 × P7 and P4 × P5) can be utilized for developing high yielding hybrid varieties as well as for exploiting hybrid vigour. These crosses also need to be evaluated further in multilocations.

Sixty cross combinations of SakkhorkhoraR and IR58025A were studied in the experimental field of Bangabundhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Salna, Gazipur during July 2010 to November 2010, to assess the character association & contribution of characters towards grain yield in restorer lines. The correlation study revealed that days to first flowering showed significant positive relationship with seed yield per plant at genotypic levels. Days to maturity showed significant positive relationship with number of tillers per plant at both genotypic and phenotypic level and effective panicles per plant at genotypic level. Plant height showed highly significant positive relationship with effective panicles per plant at both genotypic and phenotypic level. Path analysis study revealed that effective panicles per plant (0.2153) had the highest positive direct effect followed by days to first flowering (0.1492), plant height (0.0646), spikelet fertility status (%) (0.0242) and number of seeds per panicle (0.0241). Days to maturity, spikelet sterility status, effective panicles per plant, plant height, number of tillers per plant, number of seeds per panicle and spikelet fertility status had positive indirect effects on grain yield. So, based on the study days to first flowering, plant height, spikelet fertility status ,effective panicles per plant were identified as the important characters to be considered in the selection for improvement of aromatic rice genotypes.

Combining ability effects were estimated for grain yield and some other important agronomic traits of maize in a 7×7 diallel analysis excluding reciprocals. The variances for general combining ability (GCA) were found significant for yield, days to pollen shedding, days to silking and ear height while it was found non-significant for plant height and number of kernels/ear. Non-significant general combining ability (GCA) variance for plant height and number of kernels/ear indicates that these two traits were predominantly controlled by non- additive type of gene action. Specific combining ability (SCA) was significant for all the characters except yield and days to silking. Non-significant specific combining ability (SCA) variance for yield and days to silking suggests that these two traits were predominantly controlled by additive type of gene action. Both GCA and SCA variances were found significant only in days to pollen shedding and ear height indicated the presence of additive as well as non additive gene effects for controlling the traits. However, relative magnitude of these variances indicated that additive gene effects were more prominent for all the characters studied except days to silking. Parent BIL95 was the best general combiner for both high yield and number of kernels/ear and parent BML4 for dwarf plant type. Two crosses (BML4× BML36 and BIL114× BIL31) exhibited significant and positive SCA effects for grain yield involved low × average and average × average general combining parents. The range of heterosis expressed by different crosses for grain yield and days to silking was from -65.83 to 21.26 percent and -17.85 to 8.22 percent, respectively.. The better performing three crosses (BIL114×BIL31, BIL138×BIL95 and BIL31×BIL95) can be utilized for developing high yielding hybrid varieties as well as for exploiting hybrid vigour.Bangladesh J. Agril. Res. 43(4): 599-609, December 2018

Nine single cross promising maize hybrids and three check varieties (NK40, BHM9 and 900 MGold) were assessed for genotype environment interaction (GEI) and stability for the selection of promising one(s) in seven different locations of Bangladesh. The AMMI (additive main effects and multiplicative interaction) model was used to analyze the genotype-environment interaction over seven locations to select desired hybrid having higher yield and other potential attributes. Regarding genotypes (G), significant variation was found in all the characters except yield while environment (E) was found significant for all the characters. The environment of Gazipur was poor; Jamalpur, Hathazari, Ishurdi, Rahmatpur, Burirhat, and Jessore were positive environments for tested maize hybrids. Considering the mean, bi and S 2 di for all the parameters, it was evident that all the genotypes showed different response of adaptability under different environmental conditions. Among the hybrids E12 (900MG), E7(CML502 × CML491), E1(BIL95 × BIL28), E10 (NK40) and E2 (BIL95 × BIL31) were exhibited high yielder.Considering bi ̴ 1(regression co-efficient), S 2 di ̴ 0 (deviation from regression)and mean versace IPCA1 (fig1)indicated that hybrids E7and E1showed the higher yield as well as stable across locations.

Heterosis and the nature of combining ability were studied in 28 F1 hybrids made by selected 8 inbred lines using 8×8 diallel mating system (Griffing's Model I, Method IV) excluding reciprocals in maize for grain yield and yield contributing characters. The significant estimates of GCA and SCA variances suggested the importance of both additive and non-additive gene actions for the expression of the traits studied. The variances for general combining ability (GCA) were found significant for days to pollen shedding, days to silking, plant height, ear height, 1000-grain weight, and yield. Specific combining ability (SCA) was significant for all the characters except yield. Nonsignificant specific combining ability (SCA) variance for yield suggests that this trait predominantly controlled by the additive type of gene action. Variances due to GCA were much higher in magnitude than SCA for all the characters indicating the superiority of additive gene effects for the inheritance of this trait. Parents P4 and P6 were the best general combiner for high yield, P5 for grain weight and parents P7 and P8 for earliness and dwarf plant type. Seven crosses P1×P5, P1×P7, P2×P4, P3×P5, P4×P5, P4×P8, and P6×P7 exhibited positive SCA effects for grain yield. Considering BHM9 as a check, the percent heterosis for grain yield varied from-85.76 to 10.83%. Three crosses exhibited significant and positive heterosis viz. P2×P4 (10.83%), P6×P7 (9.72%) and P4×P6 (1.78%) over the check BHM9. Considering the performance of SCA effects and heterosis, two crosses P2×P4 and P6×P7 could be utilized for developing high yielding hybrid varieties as well as for exploiting hybrid potency.