STUDIES ON THE GENETIC POLYMORPHISM OF SEED STORAGE PROTEINS IN MAIZE

5. SUMMARY AND CONCLUSIONSThis study characterized and assessed genetic polymorphism of total seed storage proteins and isozymes as well as the genetic diversity among the studied six yellow maize inbred lines and their 15 F1 hybrids. The studied maize genotypes were examined for zein proteins and isozymes polymorphism using electrophoretic procedures. The level of observed genetic diversity among genotypes was assayed using two different approaches. A biochemical approach using zein storage protein banding patterns as well as isozyme banding patterns of peroxidase and esterase was performed. A traditional approach by evaluating the 15 F1 hybrids and their six parents for ten of importance agronomic traits in a replicated field trial was also performed. The relationship between genetic distances as determined by the two different approaches and combining ability as well as heterosis in all possible nonreciprocal crosses between the six parents was also assessed.The obtained results can be summarized as follows :1- A total of 22 different zein storage protein bands were present in the analyzed set of maize genotypes. These bands were present in some genotypes and absent in the other. The electrophoretic bands showed a wide variation in their molecular weight. Of these protein bands, 13 bands were found to be polymorphic.2- Differences have been occasionally noted in band intensity for apparently equivalent protein components in the patterns of different genotypes.3- Most genotypes were readily identified by SDS-PAGE, but among the 6 yellow maize inbred lines examined, one triplicate of identical zein compositions was found: P3, P4 and P5. The other inbred lines were uniquely identified by their zein protein patterns: P1, P2 and P6.4- The zymogram of peroxidase banding patterns of the six maize parents and their 15 F1¬¬¬ hybrids showed ten peroxidase anodal bands that were resolved into three major zones on the basis of migrational distance. Each zone was composed of either two or three or more isozymes depending on the genotype.5- Considerable variation in peroxidase isozyme was found among studied maize genotypes relative to the observed 10 peroxidase isozymes. Such variations was found to be higher in F1¬¬¬’s than in their parents.6- Ten anodal isozyme bands were present on the esterase zymogram of studied maize genotypes. The total esterase isozymes were resolved into two major zones. Each zone was composed of either three or seven or more isozymes depending on the genotype.7- The complex isozyme patterns seen on polyacrylamide gels of maize genotypes can be used for varietal identification to supplement the storage protein analysis.8- The presence/absence matrix of zein storage proteins as well as peroxidase and esterase isozymes was used to generate measures of the genetic distances between maize populations. The genetic distances were mostly small.9- Cluster analysis based on the genetic distance which is calculated from the zein storage protein variants separated the six parental lines and their 15 F1¬¬¬ hybrids into three major clusters and united the parental inbred lines P3, P4, P5 and P6 as well as P1 and P2 into two discrete groups within the larger cluster, which is consistent with the pedigree information.10- Based on the extent of dissimilarity among genotypes based on peroxidase and esterase isozyme band differences, the 21 maize populations were separated into four clusters.11- Cluster analysis based on genetic distance calculated from the combined analysis of zein storage protein as well as peroxidase and esterase isozyme band differences separated the six parental lines and their 15 F1¬¬¬ hybrids into ten major clusters. The Euclidean genetic distances observed indicated that the single genotype, P1 in cluster X was the most divergent from genotypes in other clusters.12- The data indicated considerable genetic divergence as determined by biochemical markers was induced by hybridization in this set of maize genotypes.13- The level of genetic diversity based on morpho-agronomical characters among maize genotypes was assayed using hierarchical Euclidean cluster analysis. The 21 maize populations were grouped into eight clusters. The Euclidean genetic distances observed indicated that the single genotype P1 in cluster VIII was the most divergent from genotypes in other clusters.14- The data indicated that distribution of genotypes into different clusters was at random and was not influenced by parentage and that no considerable genetic divergence was induced by hybridization in this set of maize genotypes.15- The correlation coefficients between genetic distance among the parents and heterosis, per se hybrid performance as well as specific combining ability exhibited by their cross combinations for grain yield were found non-significant.16- The correlation coefficient among the genetic distance estimates obtained by those two methods was of little magnitude and non-significant, indicating that those approaches are distinct and complementary divergence measures.17- The results suggested that, based either on morpho-agronomical or biochemical markers, it is not possible to differentiate maize lines with different performances and that the classification of parents from these markers is not of predictive value for developing superior hybrids.