Combining ability and heritability estimates of main agronomic characters in rapeseed breeding lines using line × tester analysis

Half F2 diallel crosses of six spring cultivars of rapeseed (Brassicanapus L.) were used to estimate heterosis effects of yield components, seed yield, oil percentage, and oil yield under limited nitrogen condition. Significant mean squares of general and specific combining abilities (GCA and SCA) were detected for pods per main axis, pods per plant, length of pod, seeds per pods, 1000-seed weight, seed yield, and oil content and oil yield indicated respectively the importance of additive and non-additive genetic effects for these traits. High narrowsense heritability estimates for 1000-seed weight, oil percentage, and oil yield indicating the prime importance of additive genetic effects for these traits. Most of the cross combinations with significant positive heterobeltiosis for seed yield had also significant heterobeltiosis effects for pods per plant and pods on main axis; therefore these traits can be used as indirect selection criteria for improving seed yield. Significant positive correlation of mean performances with heterosis and heterobeltiosis effects for most of the traits except 1000-seed weight indicated that selection of the superior crosses based on heterosis and heterobeltiosis effects will be effective for their mean performances improving these traits except 1000- seed weight. Significant positive correlation was determined between pods per plant and seed yield, indicating that this trait can be used as good selection criterion for seed yield improvement. The crosses including RAS-3/99 × RW-008911 and RAS- 3/99 × RGS-003 with high significant positive heterobeltiosis effects of seed yield were superior combinations for seed yield increasing.

Line × tester analysis of two testers of spring type and six lines of winter type oil seed rape varieties were used to estimate combining ability and heterosis of yield components and seed yield. Significant mean squares of treatments for yield components and seed yield, indicating significant genetic variations among the genotypes including parents and their crosses. Parents vs crosses mean square which indicate average heterosis was significant for all the traits except pods per plant. Line × tester mean square was significant for all the traits except pods per plant. High narrow sense heritability estimate for 1000-seed weight indicating the prime importance of additive genetic effects for this trait. Significant positive general combining ability (GCA) effects of seed yield were observed for parents which had positive GCA effects of pods per plant. Most of the crosses with significant positive specific combining ability (SCA) effects for pods per plant had significant positive SCA effects of seed yield. Most of the crosses had significant positive over spring parent heterosis of seed yield, indicating winter type of oil seed rape varieties are suitable candidates for improving this trait using combination method. Key words: Heterosis, narrow sense heritability, seed yield, oil seed rape.

The objective of the present study was to determine the genetic control and heritability of siliquae per plant at two places including without and application of nitrogen (Pp and Ps) and its related stress tolerance indices based on half diallel crosses of six spring rapeseed varieties. Significant mean squares of general combining ability (GCA) were detected for Pp and Ps and also the other related stress indices except tolerance index (TOL) and stress susceptibility index (SSI), indicating the importance of additive genetic effect. Significant mean squares of specific combining ability (SCA) were observed for all the studied traits except TOL indicating the importance of non additive genetic effects for them. Low narrow sense heritability estimates for Pp and Ps and also other associated stress indices except geometric productivity (GMP) indicated the prime importance of non additive genetic effects for these traits except GMP. Most of the crosses had significant SCA effects of siliquae per plant at non application of nitrogen condition, therefore selection of combinations based on SCA effect of Ps will be more efficient than SCA effect of Pp. The variations of SCA effects of the crosses for mean productivity (MP) and GMP are higher than the other stress indices, so selection of the crosses based on this two stress indices will have sufficient gain. High parent heterosis effects of TOL, STI and SSI were more variated than SCA effects, therefore selection based on high parent heterosis effects will be more efficient than SCA effects.

Six parents and their 15 F2 diallel progenies, totally 21 genotypes, were evaluated for genetic parameters of quantitative characteristics. The traits of interest were growing degree days (GDDs) from sowing to the flowering (DDF), to end of flowering (DDE), flowering period (DFP), to maturity (DDM) and seed yield (SY). Significant mean squares of general combining ability (GCA) was exhibited for DDF, DDE, DFP, DDM and seed yield indicating significant differences of GCA effects of parents for these traits. Significant mean squares of specific combining ability (SCA) for all the traits exhibited the importance of non additive genetic effects for the traits. Significant ratio of MS(GCA)/MS(SCA) and high narrow sense heritability estimates for DDF, DDE, DDM indicating the prime importance of additive genetic effects for controlling these traits. DFP was also less heritable than the other phonological traits, so the efficiency of selection for this trait will be low. All of the combinations with significant negative SCA effects for DDM had at least one parent with significant negative GCA effect for this trait. PF7045/91 with significant positive GCA effect of SY, was best combiner for improving SY. Significant positive correlation between DDM and each of two traits including DDF and DDE, indicating these traits can be used as indirect selection criteria for improving DDM.

Line × tester analysis of twenty lines and three testers of Indian mustard (Brassica juncea L. Czern & Coss.) cultivars were used to estimate general combining ability (GCA), specific combining ability (SCA) effects, high parent heterosis and narrow-sense heritability estimate for plant height, yield components and seed yield. Significant variance of line x tester for the traits like pods per plant and seed yield indicating non additive genetic effects have important role for controlling these traits. Significant mean squares of parents v/s crosses which are indicating significant average heterosis were also significant for all the traits except seeds per pod. High narrow-sense heritability estimates for all the traits except seeds per pod exhibited the prime importance of additive genetic effects for these traits except seeds per pod. Most of the crosses with negative SCA effect for plant height had at least one parent with significant negative or negative GCA effect for this trait. For most of the traits except pods per plant, the efficiency of high parent heterosis effect was more than SCA effect for determining superior cross combinations.

Combining ability of yield associated traits has been studied quite frequently in oilseed rape (Brassica napus L.) but it was hardly ever studied based on nitrogen levels variations. Six parents along with their 15 F2 half diallel crosses were evaluated in two nitrogen (N) levels including N0 and N+. Analysis of variance revealed significant mean squares of general and specific combining abilities (GCA and SCA) for all the traits studied. The high narrow-sense heritability estimates were found for seed yield and harvest index, implying the more importance of additive genetic effects for and consequently high selection efficiency for improving these traits. Due to low narrow-sense heritability estimates for oil and protein contents and therefore more importance of non-additive genetic effects, selection for improving these traits should be done in later segregating generations. The GCA × N level interaction was significant only for oil content which is indicating of more differences of GCA effect of this trait at two nitrogen levels. Significant N × SCA effect mean squares for harvest index and oil content, revealed significant variation of SCA effects of these traits in nitrogen levels application. Most of the crosses with high seed yield at N0 and N+ had at least one parent with positive GCA effect at both N levels. Among the six parents, PF7045/91 appeared to be the best combiner for seed yield at the N0. This variety also showed high GCA at the N+ but its low oil content at the N+ is certainly disadvantageous as the quality of the hybrid is often intermediate between the two parents.

Fifteen F 2 progenies derived from a 6x6 half diallel crosses along with their parents of rapeseed (Brassica MpUS L.) varietie5 were evaluated for pods per main axis, pods per plant, length of pod, seeds per pod, 1000- seed weight , grain yield and oil content The Analysis of variance based on Griffing's method two, with mixed-B model on F 2 progenies and their parents revealed significant mean squares for general combining ability (GCA), specific combining ability (SCA) indicating that both additive and non-additive genetic effects were involved in controlling these traits. High narrow-sense heritability estimates and degree of dominance less than one were observed for length of pod and 1000-seed weight indicated the prime importance of additive genetic effects for controlling these two traits. Narrow-sense heritability estimates for pods per main axis, pods per plant, seeds per pod, grain yield and oil content were estimated 0.22, 0.14, 0.30, 0.15 and 0.08, respectively concluded that the importance role of non-additive genetic effects for controlling these traits. Among yield components, pods per main axis and pods per plant had significant positive correlation with grain yield (0.54* and 0.60**), so any changing of these traits would have significant effects on grain yield. Based on the results of factor analysis on GCA effects revealed that pods per main axis, pods per plant and grain yield had high coefficients of factor loading in the factor one, but on SCA effects pods per main axis, pods per plant and 1000- seed weight had high coefficients of factor loading and the same direction of variation.

Line ×tester of six lines and two testers of spring rapeseed (<i>Brassica napus </i>L.) cultivars were used to estimate general combining ability (GCA), specific combining ability (SCA) effects, high parent heterosis and narrow-sense heritability estimate for plant height, yield components and seed yield. Significant variance of line x tester for pods per plant and seed yield, indicating non additive genetic effects have important role for controlling these traits. Significant mean squares of parents vs crosses which are indicating significant average heterosis were also significant for all the traits except seeds per pod. High narrow-sense heritability estimates for all the traits except seeds per pod exhibited the prime importance of additive genetic effects for these traits except seeds per pod. Most of the crosses with negative SCA effect for plant height had at least one parent with significant negative or negative GCA effect for this trait. For most of the traits except pods per plant, the efficiency of high parent heterosis effect was more than SCA effect for determining superior cross combinations.

Information on estimates of combining ability of the promising lines of breeding material is important for evolving higher yielding varieties of oilseed rape (Brassica napus L.). An experiment was conducted to quantitatively examine the genetic parameters of phenological traits, plant height, pods on main raceme, pods per plant and seed yield for eight oilseed rape genotypes using a half-diallel crosses. The result of the diallel analysis revealed significant mean squares of general and specific combining abilities (GCA and SCA) for all studied traits, indicating the importance of additive and non-additive genetic effects for these traits. On the other hand estimation of high narrow-sense heritability estimates for days to flowering, duration of flowering and pods on main raceme, indicated the prime importance of additive genetic effects for these traits. L420 and L401 with significant negative GCA effects for days to flowering and days to maturity were suitable for yielding early maturity combinations. L41, Zafar and L22 with significant positive GCA effects for seed yield were superior parents for increasing seed yield. The crosses with significant positive SCA effects for seed yield had at least one parent with significant positive GCA effects for this trait. The crosses including L41×L22, L41×LF2, Zafar×L22 and Zafar×L420 with seed yield of 3421.7, 3400, 3348.1 and 3311.3 kg ha-1 could be promising for determination of superior recombinants for high seed yield coupled with other growth characters in advanced generations of segregation.

Although an average plant height is more preferable in most of agronomic crops, less reduction of this trait in stress condition makes yield components and seed yield sustainable in rapeseed varieties. Combining ability, heterosis and heritability of plant height at application and non-application of nitrogen environments (Hp and Hs, respectively) and its related stress tolerance indices were detected in half F2 diallel crosses of six spring rapeseed varieties. Significant mean squares of general and specific combining abilities (GCA and SCA) were detected for Hp, Hs, mean productivity (MP), geometric mean productivity (GMP) and stress tolerance index (STI), indicating the importance of additive and non-additive genetic effects for them. A high narrow-sense heritability estimate was exhibited for STI, emphasizing the prime importance of additive genetic effects for this stress tolerance index. A significant correlation among Hp, Hs, MP, GMP and STI showed the efficiency of these stress indices for improving plant height in plant breeding programme. In comparison to SCA effects, most of the crosses had significant high parent heterosis for Hp, Hs and all the stress indices. RGS003 with a significant positive GCA effect of Hs was considered as a suitable parent for improving this trait and most of the combinations of this genotype had significant negative SCA effects.

Genetic improvement in a crop, viz. Brassica species, through plant breeding essentially requires the presence of adequate genetic diversity within the gene pool. Winter rapeseed is known to be genetically different from spring rapeseed and can therefore be used for extending genetic diversity in the progenies produced via crossing methods. Using line?tester analyses of two spring types of testers and six lines of winter-type rapeseed varieties, heterotic patterns of phenological traits, plant height and seed yield were estimated. Significant mean squares between parents and crosses revealed significant heterosis for all the traits. Line?tester mean squares, indicating the non-additive genetic effects, were significant only for plant height and seed yield. High narrow-sense heritability estimates for phenological traits underline the importance of additive genetic effects and thus the efficiency of selection for improving these traits. Based on the significant and positive expression of heterosis effects for phenological traits and plant height in the winter parents, it was concluded that the F1 progenies had earlier and shorter maturity than the winter parents. F1 progenies were also early flowering, early maturing and taller than the spring-type parents. Significant positive heterosis of the crosses for seed yield was observed in 75% and 42% of F1 progenies compared to the spring and winter parents, respectively, indicating a higher yield potential of the F1 hybrids than the spring and winter parents.

The combining ability of quantitative and qualititative traits has been studied quite frequently in rapeseed (Brassica napus L.), but rarely at different nitrogen levels. Twenty-one genotypes, including 6 parents and their 15 F2 diallel progenies, were evaluated at two nitrogen rates, N0 and N150. A combined analysis of variance revealed significant mean squares of general (GCA) and specific (SCA) combining abilities for all of the traits. The nitrogen × GCA mean square was not significant for all of the traits, indicating the stability of additive genetic effects in different environments. Days to end of flowering, days to maturity, oil content and oil yield had significant nitrogen × SCA mean squares, which showed significant variation of SCA effects on these traits at different nitrogen levels. Days to flowering, days to end of flowering and days to maturity showed high narrow-sense heritability at two nitrogen levels, but plant height and seed yield had high narrow-sense heritability estimates at N0. Most of the crosses had significant positive or negative SCA effects for seed yield at N0; however, at N150 only two crosses had significant SCA effects. Therefore, selection of hybrids based on SCA effects at N0 would be more effective.

Eight yellow maize (zea mays L.) inbred lines were crossed in half diallel mating scheme in 2013 season at Gemmeiza Agric.Res.Station giving a total of 28 crosses as hybrid seeds.In 2014 summer season, these 28 crosses were evaluated in a randomized complete blocks designs experiment with four replications at two locations and two densities i.e. 20 cm (D 1 ) and 25cm (D 2 ).Gemmeiza (L 1 ) and Mallawy (L 2 ).The whole study was designated as four different environmental conditions (L 1 D 1 , L 1 D 2 , L 2 D 1 and L 2 D 2 ) in each experiment.location mean squares had significant and high significant for days to 50% tasseling, plant height, ear height, ear length, number of rows / ear, number of kernels / row and grain yield (ard / fad. ) at D 1 and D 2 .While, ear diamater and 100-kernel weight at D 1 and days to 50% silking at D 2 had significant location mean squares.Mean squares of densities exhibited significant and high significant for days to 50% tasseling and silking at L 2 and ear diameter at L 1 .While, plant and ear heights, ear length, 100-kernel weight and grain yield / fad.had significant mean squares of densities, indicated that these traits changed their performance from location to another.Crosses mean squares were high significant for all traits under locations and densities meaning that, differences among the crosses under locations and densities were exited.Crosses x locations interaction mean squares had highly significant for days to 50% tassling, days to 50% silking and ear height at D 1 .Crosses x densities interactions mean squares had significant differences at four environments for most traits The interactions between crosses with the partitions; locations (L), densities (D) and (L x D) were significant for all traits, meaning that the crosses were affected by change of locations, densities and interaction of locations x densities.

Half diallel crosses of eight spring genotypes of oilseed rape (Brassica napusL.) were considered to evaluate heterobeltiosis effects of plant height, yield component characters, seed yield and harvest index. Significant mean squares of general and specific combining abilities (GCA and SCA) were determined for all the traits except 1000-seed weight demonstrating prominence of additive and non additive genetic effects for the mentioned traits. Narrow-sense heritability estimates were high for siliquae on main raceme and 1000-seed weight representing the major importance of additive genetic effects for the characters. Most of the crosses with significant positive high parent heterosis for seed yield had also significant heterotic effects for siliquae per plant; therefore, this trait can be considered as indirect selection criterion for enhancing seed yield. Seed yield was significantly correlated with the traits including plant height, siliquae on main raceme and siliquae per plant based on mean performances of the traits and this result was confirmed with correlations based on heterobeltiosis. The crosses including L41×LF2 and L31×L401 with highly significant heterobeltiosis estimates of grain yield were superior combinations for breeding this trait. which proved good specific combiners for most of the traits.

The objectives of this research were to investigate the genetic structure of the 20 F1s rapeseed hybrids established from five female moderate maturing lines and four early maturing male testers, determine parents showing general combining ability (GCA) and assess crosses demonstrating specific combining ability (SCA). Significant mean squares of lines and testers determined GCA and confirmed the presence of additive genes that were influencing the traits, while the significance of line×tester interactions indicated the importance of SCA of parents and demonstrated the importance of dominance or non-additive genetic effects. Significant variance of parents vs. crosses revealed significant average heterosis for all the traits except first pod height and seeds per pod. High narrow-sense heritability estimates for number of branches and pod length indicated the importance of additive genetic effects for these traits. Significantly positive correlation was exhibited between GCA effects on pods on main raceme and seed yield and, therefore, the GCA effect on pods on main raceme can be used as indirect selection criterion for improvement of seed yield. The crosses L41×Foma2, Zafar×R42 and L22B×R38 recorded significant positive SCA effects and high mean values of seed yield of 3400, 3311.3 and 2904.2 kg ha-1, respectively.