Combining Ability Analysis for Some Polygenic Traits in a 5X5 Diallel Cross of Bread Wheat (Triticum aestivum L.)

MATERIALS AND METHODS

Experiment was carried out in the Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad. The experimental material comprising five different lines/varieties of spring wheat, namely Uqab 2000, Pasban-90, Fsd.83, 8779 and 5039 were crossed in a diallel fashion during crop season 2001-2002.

At maturity seeds were collected from parents and their hybrids. Seed of F₁^,s were sown in the field along with their parents in a triplicated Randomized Complete Block Design during 2nd week of November, 2002. The seeds were dibbed in rows. Each replication had one row of 5 m length for each treatment while plant-to-plant and row-to-row distance was 15 and 30cm, respectively. Two seeds per hole were sown and later thinned to single seedling per site. Other cultural and agronomic practices were kept constant for the whole experiment. Ten guarded plants from each row were taken randomly and data were recorded for flag leaf area, plant height, number of fertile tillers per plant, peduncle length and spike length. Analysis of variance techniques of Steel and Torrie^[7] were applied to determine the significance among genotypes and where the differences were significant, data were further subjected to combining ability analysis. The GCA and SCA estimates were calculated according to Griffing^[1] using Method I, Model II. Estimates of GCA, SCA, reciprocal effects and their components of variance were calculated from the mean values of F₁ data.

RESULTS AND DISCUSSION

The combining ability analysis revealed that mean squares due to general combining ability effects were found to be highly significant for flag leaf area. The mean squares due to specific combining ability and reciprocal effects were non-significant for this character (Table 1). Varieties, Fsd.83 and Pasban-90 were good combiners with general combining ability effects of 2.670 and 1.665, respectively. The lowest general combining ability effects for flag leaf area were observed for the line 8779, Uqab 2000 and 5039 with negative values of -2.267, -0.240 and -1.828, respectively (Table 2). Among crosses Uqab 2000 x 8779 was top scorer for specific combining ability effects with the value of 1.283 closely followed by Pasban-90 x 5039 (1.139). Cross combinations Pasban-90 x 8779 and Pasban-90 x Fsd.83 with the respective values of -0.885 and -0.373 were the poor specific combiners (Table 3). The cross combination 8779 x 5039 produced the highest value (1.552) for reciprocal effects for flag leaf area, followed by Uqab 2000 x 8779 (0.882). The poorest value was exhibited by the hybrid Uqab 2000 x 5039 (-1.633) (Table 4). The variance due to general combining ability effects was more than specific combining ability effects showing the additive type of gene action (Table 5). These results are in accordance with findings of Mahmood and Chowdhry^[2] while Mohy-ud-din and Shahzad^[8] reported that SCA was more than GCA for flag leaf area. The deviation may be due to different environment in which experiment was conducted.

The combining ability analysis depicted that the mean squares for general combining ability and reciprocal effects were found to be non-significant for plant height while the mean squares due to specific combining ability were found to be highly significant (Table 1).

The desirable results regarding the general combining ability estimates for plant height were obtained in the line 8779 which possessed the lowest negative value of -1.902 because the short stature plants are preferred. Then the genotype Pasban-90 with the negative value of-0.623 was the next scorer for general combining ability effects. Line 5039 gave the highest results, which is un-desirable for plant height with a value of 1.300 (Table 2).

Table 1:	Combining ability mean squares values for different parameters in a 5 x 5 diallel cross of wheat
NS = Non-Significant. * = Significant at 5% level of probability. ** = Significant at 1% level of probability

Table 2:	Estimates of general combining ability for different parameters in a 5 x 5 diallel cross of wheat

Table 3:	Estimates of specific combining ability effects for different parameters in a 5x5 diallel cross of wheat

Table 4:	Estimates of reciprocal effects for different parameters in a 5x5 diallel cross of wheat

Table 5:	Estimates of components of variation due to general, specific combining ability and reciprocal effects for different parameters in a 5x5 diallel cross of wheat
Values in the parenthesis indicate the percentage of variance components

Similarly desirable results regarding the specific combining ability effects for plant height were observed in cross combination Pasban-90 x 8779, which possessed the negative value of-1.851 because the short stature plants are preferred. Cross combination, Pasban-90 x 5039 and Fsd.83 x 5039 with the negative values of -1.814 and -1.662, respectively were the next scorers for specific combining ability effects. Cross combination 8779 x 5039 gave the highest value (2.546), which is undesirable for plant height (Table 3). Regarding the reciprocal effects the desirable results were exhibited by the hybrid Pasban-90 x 8779 (-1.125), followed by the hybrid Pasban-90 x 5039 (-1.010). Cross combination 8779 x 5039 gave the highest results with positive magnitude (0.472), which is undesirable for this traits (Table 4).

The variance due to specific combining ability effects was more than general combining ability showing non-additive type of gene action (Table 5). Similar findings were reported by research worker like Mishra et al.^[3], while Lakshmi et al.^[9] reported that general combining ability effects were more than the specific combining ability effects showing additive type of gene action. The present results are not in support of them, may be due to difference of genetic material and environment.

The combining ability analysis indicated that the mean squares due to general and specific combining ability were found to be highly significant for number of fertile tillers per plant, while the mean squares due to reciprocal effects were non-significant for this trait. Among parents 5039 proved to be the best combining line with general combining ability effects of 0.719. Genotype Pasban-90 stood second attaining the value of 0.173 and Fsd.83 showed the lowest general combining ability effects with negative value of-0.391 (Table 2). Among cross combinations, the highest value of 0.511 for specific effects was attained by Pasban-90 x Fsd.83 followed by cross Uqab 2000 x Fsd.83 with the value of 0.404. Cross combination Pasban-90 x 8779 gave the lowest value of -0.249 (Table 3).

Regarding the reciprocal effects the highest value of 0.283 was exhibited by the cross combination Fsd.83 x 5039, followed by Uqab 2000 x 5039 for number of fertile tillers per plant having the value of 0.167. The lowest value (-0.400) was recorded for the cross 8779 x 5039 (Table 4).

The variance due to general combining ability was higher than the specific combining ability showing additive type of gene action (Table 5). The present results are therefore supported by the findings of Chowdhry et al.^[5] while Sangwan and Chaudhary^[10] observed high specific combining ability for number of fertile tillers per plant. The deviation may be due to different environment in which the experiments were conducted.

The mean squares due to general combining ability and reciprocal effects were found to be non-significant while the mean squares due to specific combining ability were highly significant for peduncle length (Table 1). Table 2 indicates that the highest general combining ability effects were observed for the line 5039 with the value of 1.260 while Uqab 2000 showed the lowest value of GCA effects, (-0.928). It is apparent from Table 3 that the hybrid Fsd.83 x 5039 was the best specific combiner for peduncle length possessing the highest value (1.1930) followed by the cross Uqab 2000 x Pasban-90 (1.006). The hybrid Pasban-90 x 8779 showed the poorest performance for peduncle length having the lowest value of SCA effects (-2.042). In case of reciprocal effects the highest value (0.885) for peduncle length was exhibited by the hybrid 8779 x 5039, followed by Uqab 2000 x Pasban-90 (0.032). The lowest magnitude of reciprocal effects (-1.633) was observed in hybrid Pasban-90 x 8779 (Table 4).

The variance due to specific combining ability effect was much higher than that of general combining ability showing non-additive type of gene action (Table 5). The results are in accordance with the findings of Atiq-ur-Rehman et al.^[4], while Chaudhry et al.^[11] observed high general combining ability for peduncle length. The present results are not in support of them, may be due to difference of genetic material and environment.

The mean squares due to general combining ability were found to be significant for spike length while the mean squares for specific combining ability and reciprocal effects were non-significant for this character (Table 1). Maximum general combining ability effects were shown by the genotype Fsd.83 with the value of 0.593 and variety Pasban-90 exhibited the lowest value of general combining ability, i.e.,-0.471 (Table 2). Among cross combinations the hybrid Uqab 2000 x 5039 showed the excellent performance with highest specific combining ability value (0.349) followed by Fsd.83 x 8779 (0.320). The poorest performance was exhibited by the hybrid Uqab 2000 x Fsd.83 with the lowest negative value (-0.262) for this trait (Table 3). Cross combination 8779 x 5039 with a value of 0.903 gave the highest reciprocal effects for spike length, followed by crosses Uqab 2000 x 8779 and Fsd. 83 x 5039 with the respective values of 0.367 and 0.328. The lowest reciprocal effect (-0.627) was shown by the cross Uqab 2000 x Pasban-90 (Table 4).

The variance due to general combining ability was greater than that of specific combining ability showing additive type of gene action (Table 5). The results are in accordance with the findings of Sudesh et al.^[6], while Atiq-ur-Rehman et al.^[4] observed high specific combining ability for spike length. These results are not in favour of them, may be due to difference of genetic material and environment.