Inheritance of Seed Hardness and Seed Coat Weight in Faba Bean (Vicia faba L.)

Abstract

1- The main objective of this research has been to study the magnitude of gene action controlling the inheritance of seed hardness and seed coat weight of faba bean (Vicia faba L.). in F1, F2 and their respective parents. Eight genotypes of faba bean were used as parents in this study. The eight parents were selected in season 2000/2001 according to their variability in seed hardness and seed coat weight. They were divided into tow groups, low hard seeded parents (< 5.0% hard seeds) and high hard seeded parents ( =502; 12.0% hard seeds). 2- In the first season (2001/2002), the eight parents were crossed in a half diallel way producing 28 F1 hybrids. In the second season (2002/2003), the eight parents, together with the 28 F1 hybrids were grown in a therano cage for selfing and the F2 seeds were obtained. The parents, F1 hybrids and F2 i.e. a total of 64 genotypes, were grown in the third season. A randomized complete block design with two replications was used to test the material. At harvest, in the later two seasons (the evaluation seasons), data were collected, on mean bases, for the following four parameters: number of pods/plant, number of seeds/plant, 100-seed weight(g), and seed yield/plot (g). The percentages of the two seed quality characters, seed hardness and seed coat weight, were determined as described by Salih (1982). 3- The genetical analysis was performed using Hayman (1954, 1958) method to determine the magnitude of gene action controlling the inheritance of seed hardness and seed coat weight. Also Griffing (1956) Method 2, Model 1, was used for combining ability analysis. Both analysis of components of genetic variations and the (wr,vr) graphs revealed seed hardness as a dominant character and the non-additive gene effects (b, H1 and H2) were more important in the inheritance of this character. Ambidirectional dominance of the character and un equal distribution of genes also were detected . The mean degree of dominance [(H1/D) ½ ratio, and the interception points, a ] indicated an over dominance in the inheritance of seed hardness. Also a predominance of the dominant alleles in the parents used was observed, where positive F and Fri estimates and negative r values were obtained. A group of two to three genes were detected in the inheritance of seed hardness, among them a single dominant gene was detected. Regarding the inheritance of seed coat weight, the results revealed that the character was under the control of both additive and non-additive gene action. However, the dominant component of the genotypic ratio (H1) was more important. Ambidirectional dominance of the character was observed (b1 is not significant) and the non-additive genetic components , H2, b2, were significant in both F1 and F2 indicating unequal distribution of genes in the parents used. Positive F estimates were obtained in the two generations indicating that, dominant alleles were more frequent than recessive ones. Three to four genes were found to control seed coat weight indicating its quantitative inheritance. Among them one gene was dominant. Partial dominance was shown by F2 and F1 in the 2nd evaluation season (F1 2004) , while F1 in the first evaluation season (F1 2003) exhibited over dominance. In the (wr,vr) graph analysis, different and contradicting results were obtained. The slopes of the regression lines in F1 (2004) and F2 were significantly different from zero and unity indicating the presence of gene interaction in the material used. The interception points were below the origin in the three graphs indicating over dominance in the two generations. The array points tacked nearly constant orders between graphs. 4- By the combining ability analysis, seed hardness showed significant specific combining ability (sca) in both evaluation seasons and general combining ability (gca) in the first evaluation season only. The contribution of gca and sca for both seed coat weight and 100-seed weight were significant indicating that both additive and non-additive gene actions determine the expression of these traits. The non-additive genetic variance (sca) was found to be more important than the additive genetic variance (gca) for number of pods/plant and number of seeds/plant. For seed yield, both components of genetic variance were nonsignificant. The parents C.28 and C.86/1 gave the desirable gca effect for all studied traits. Thus they were the good general combiners for these traits in this research. On the other hand, the parent Bulk/1/1/2 showed undesirable effects for all studied characters. Most of the crosses exhibited nonsignificant sca effects for all traits. But, the crosses C.28 =620; C.86/1 and ZBF/1/1 =620; C.28 had desirable sca effect for all characters. 5- Yield/plot exhibited significant associations with number of pods/plant, number of seeds/plant and 100-seed weight. High significant and positive associations were observed between number pods/plant and number of seeds/plant. Seed hardness showed positive and significant correlation with seed coat weight and nonsignificant associations with yield and its components in the two seasons. 6- The effect of pods location on the stalk of the plant on the seed hardness and seed coat weight was studied. The pod position had a significant effect on seed hardness in the two seasons. The lower pods showed the greater grand mean for hard seed percentage in the two seasons. Neither the pods position, nor the interactions had significant effect on seed coat weight. 7- Also the seed coat structure of faba bean seed was studied. One line was selected from the high hard seeded group, C.36, and another one from the low hard seeded group, C.28. Transverse sections were prepared from a soft and hard seeds of each line, at the micropyle region and regions away from the micropyle . Photomicrographs were taken from these two regions and measurements (in microns) were recorded about the seed coat thickness, palisade layer, hourglass cells layer, the micropyle and the trachids for all four groups. The main difference between the two lines and between the soft and hard seeds of each line was in the size of micropyle and trachids, which were responsible for water intery to the seeds. The hard seeds had smaller micropyle opening and smaller trachids than soft seeds.