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Abstract
The present investigation was carried out to study heterosis, combining ability means of diallel cross system in sowing dates. A half diallel cross set involving ten yellow inbred lines namely: P1 (1012), P2 (106), P3 (103), P4 (100), P5 (161), P6 (120-B), P7 (1006), P8 (L-56), P9 (313-A) and P10 (500) were used in this concern to evaluate the parents and their possible 45 hybrids as well as the two checks S.C. G. 155 and Pioneer 3062. The two adjacent experiments were conducted at early and late sowing dates. A complete randomized block design with three replications was carried out at the Agricultural Research and Experimental Station of the Fac. of Agric., Moshtohor.
Data were recorded on 10 guarded plants randomely sampled from each plot. The data obtained for each trait were statistically analyzed on individual plant mean basis except tasseling, silking and maturity dates where the plot mean basis were used in this concern. An ordinary analysis of variance was firstly performed for each experiment, and thereafter a combined analysis was carried out whenever homogeneity of error variance was detected. Heterosis was computed as mean squares and as the percentage deviation of F1 mean performance from each two checks hybrids i.e. S.C. G. 155 and Pioneer 3062 average values for individual crosses. General and specific combining ability estimates were obtained by employing Griffing’s (1956) diallel cross analysis designed as method 2 model 1.
The obtained results could be summarized as follows
5.1.1. Analysis of variance and mean performance
1- Sowing dates mean squares were highly significant for all traits under the study except ears/plant and shelling percentage, with mean values in early sowing being higher than those in late sowing for all traits except ear husk.
2- Genotypes mean squares reached the significance level of probability for all traits in both sowing dates as well as the combined analysis except, ears/plant in late sowing date. Significant genotypes x sowing date mean squares were obtained for all traits except ear height, ear husk, ear diameter, rows/ear and shelling percentage., revealing that the performance of genotypes differed from sowing date to another.
3- Appreciable parents, mean squares were obtained for all traits except ears/plant at both sowing dates as well as the combined analysis. Insignificant interaction mean squares between parental inbred lines and sowing dates were detected for all traits studied except tasseling date, silking date, plant height, ear diameter and shelling percentage.
4- Hybrids mean squares were significant for all traits except ear diameter, no. of ears/plant at late sowing and shelling percentage at early sowing date revealing over all differences between these hybrids. Significant interaction between hybrids by sowing dates mean squares were obtained for all traits except ear height, ear husk, ear diameter, no. of rows/ear and shelling percentage.
5- The inbred line no. 2, 5, 6, 8 and 10 in early sowing date, no. 8, 10 and 2 in late sowing date, no. 2, 5, 6, 8 and 10 at the combined analysis, behaved as the earliest inbred lines for maturity date. While, the parental inbred lines no. 4, 5 and 7 had the highest mean values for ear weight and grain yield/plant. The cross 2x7 gave the lowest mean values of plant and ear heights.
6- For grain yield/plant, eight hybrids 1x8, 1x9, 1x10, 2x9, 4x8, 5x6, 6x8 and 6x10 in the combined analysis had significant superiority over the best check hybrids S.C. G.155 and S.C. Pioneer 3062.
5.1.2. heterosis
Heterosis mean squares were significant for all traits except no. of ears/plant at both sowing dates as well as the combined analysis. Insignificant interaction mean squares between parents vs. crosses and sowing date were obtained for all traits except maturity date, ear and grain yields/plant and shelling percentage.
The crosses 1x8 and 4x8 in both sowing dates as well as the combined analysis, both crosses 1x10 and 6x7 in early sowing date and the combined analysis, both crosses 1x9 and 5x6 in late sowing date, 2x5 in early sowing date and 6x10 in the combined analysis out yielded the two checks hybrids (S.C. G.155 and S.C. Pioneer 3062). The useful heterotic effects relative to S.C. G. 155 ranged from 8.91 to 25.02% and from Pioneer 3062 ranged from 6.60 to 26.39% in the combined analysis.
5.1.3. Combining ability
5.1.3.A. Analysis of variance
1- The mean squares due to general and specific combining ability were highly significant for all traits except no. of ears/plant in the late sowing date.
2- For ear husk, maturity date, no. of rows/ear in both sowing dates as well as the combined analysis, tasseling date, silking date, no. of ears/plant and shelling percentage in early sowing date and the combined analysis, high ratios which largely exceeded the unity were obtained, indicating that a large part of the total genetic variability associated with theses traits was a result of additive and additive by additive gene action.
3- Plant height, ear height, ear length, ear diameter, no. of grains/row, 100-kernel weight, ear weight/plant and grain yield/plant in separate sowing date as well as the combined analysis, showed GCA/SCA ratios less than unity.
4- Tasseling dates and shelling percentage at the late sowing date had GCA/SCA ratio equal unity, indicating that additive and non-additive types of gene action have the same importance in the performance of these cases.
5- The mean squares of interaction between sowing dates and both types of combining ability were significant for tasseling date, silking date, and plant height, no. of grains/row, ear weight and grain yield/plant.
6- The ratio for GCA x D/GCA was higher than ratio of SCA x D/SCA for tasseling date, plant height, no. of grains/row, ear weight and grain yield/plant. This result indicated that additive effects were more influenced by the environmental conditions than non- additive genetic effects of these traits.
5.1.3.B. Combining ability effects
I) General combining ability effects
The parental line no. 1,2 and 4 for shortness of plant and ear height, inbred line no. 6 and 8 for earliness and inbred line no. 5, 6 and 10 for grain yield/plant at both sowing date as well as the combined analysis gave significant desirable effect.
II) Specific combining ability
The most desirable inter- and intra-allelic interactions were presented by P2xP7 for ear height P1xP7, P1xP8, P1xP10, P2xP10 P4xP6, P5xP8 and P7xP9, for ear husk, and all hybrids except of P1xP2, P1xP3, P1xP4, P2xP6, P2xP7, P3xP9, P4xP6, P5xP7, P8xP9 and P8xP10 for grain yield exhibited significant positive effects for one or more of yield components. However, the most desirable SCA effects for grain yield/plant were detected for the crosses P1xP8, P2xP9 and P1xP10 being 67.22, 54.41 and 53.40, respectively. These crosses may be prime importance in breeding programmes either towards hybrid maize production or synthetic varieties composed of hybrids which involved the good combiners for the traits in view.
5.2. The second experiment
DNA fingerprinting using Random Amplified Polymorphic DNA (RAPD)
5.2.1. RAPD polymorphism
a. The results revealed that, the five primers scored a total of 143 amplified DNA bands. The number of bands varied from (16) bands for (B13) primer to (45) bands for (A13).
b. Total number of fragments varied from 3 fragments for ( B12 and B19) to 9 for (A13 and B3 ).
c. Number of polymorphic fragments varied from 1 for B12 to 8 for (A13 and B3)
d. The five RAPD primers generated 143 scorable bands across 10 inbred lines. These primers produced a total of 32 reproducible fragments, from which 26 (73.06%) were polymorphic. The mean of polymorphic bands per primer was 5.2. The size of fragments ranged from 144.72 bp to 16778.08 bp.
5.2.2. Genetic similarities and clustering
a. The lowest genetic similarity (0.333) was obtained between the two inbred lines P2 and P9, while, the highest genetic similarity (0.81) was scored between the two inbred lines P10 and P9. The overall mean for genetic similarity among all inbred lines under study was (0.522)
b. Dendrogram constructed with UPGMA cluster analysis of RAPD data shows the genetic relationships among ten inbred line, The data collectively distinguished two main clusters. The first main cluster consist of six inbred lines separatly into two sub clusters. the second sub cluster contained the other four inbred lines.
5.2.3. The correlation between genetic distance and each of mean performance, SCA and heterosis for grain yield/plant
The estimated value for correlation coefficient between genetic diversity (GD), and each of mean performance and heterosis relative to both checks varietes and SCA for grain yield/plant were significant (r = 0.315, 0.332, 0.334, 0.401), respectively. The correlation coefficient between sub cluster1 (inbred lines P1 and P2) and main cluster 2 (inbred lines P7, P8, P9and P10) was higher (r = 0.56). In the same time the highest values of grain yield and heterosis were obtained from the crossing between inbred line P1 (sub cluster 1) and inbred line P8 (main cluster 2). Also crossing between inbred line P1 (sub cluster 1) and inbred line P10 (main cluster 2) ranked the third for grain yield, specific combining ability and heterosis. While the crosses P6xP8 and P6xP10 derived from inbred line P6 (sub-sub cluster 2) and P8 and P10 (main cluster 2) had the fourth rank for grain yield and heterosis, The results indicated that RAPD marker can be used as a tool for determining the extent of genetic diversity among maize inbred lines and classiting genotypes into different groups. This study showed that GD can be used to precisely predict the yield performance and heterosis value for F1 hybrids.