By developing molecular genetics methods, based on PCR technology or not, the genome could be dissected at the level of DNA and different types of DNA molecular markers are available for comprehensive evaluation of the relationship among maize (Zea mays L.) inbred lines, maize hybrids and parental inbred lines at the level of DNA. Biochemical processes leading to nuclear gene expression in eukaryotic cells are going on at the level of chromatin. At this stage nuclear DNA and other nuclear components are organised in the nucleus in a highly ordered way to achieve a perfect synchronisation and accuracy of the various structural/functional processes occurring in a differentiated cell. DNA markers are good tools for the determination of genotype polymorphism at the level of DNA and identification of genotypes based on DNA polymorphism. The question is which part of DNA polymorphism, determined by DNA markers, corresponds to functional genome polymorphism. A good example is when several physiologically different traits of plant development are mapped by one and the same molecular probe or when one and the same developmental trait is mapped to several widely distant loci (Khavkin and Coe, MNL70:42-45, 1996) and especially in the case when protein overexpression is posttranscriptionally regulated. A particularly important question arises when investigation of the biochemical background of the heterotic effect is under way. Somatic cells of dry embryo tissue after inbred line crossing, as well as all somatic cells during development of the F1 plant, carry chromatin of both parental lines. The highest heterotic effect is expressed in the somatic tissue of the F1 plant generation. Therefore we set up an experiment to answer the question: Could dry embryo salt soluble proteins be informative genetic markers in the investigation of genetic distance, genotype identification and genetic background of heterotic effect as well? In this paper we are presenting results on genetic relationships among inbred lines based on embryo salt soluble proteins.
Analysed maize genotypes, including both Corn Belt public lines and inbreds created at the Maize Research Institute "Zemun Polje" (MRI) are listed in Table 1.
Table 1. Genetic background of analysed inbred lines
|B73 Sbms||B73 rec.|
|ZPL326||BSSS, MRI developed germplasm|
|ZPL385||MRI developed germplasm with exotic component|
|Mo17||CI 187-2 x C103|
|ZPL412||Yu pop x Mo17|
|ZPL395||(Yu pop x Mo17)Mo17|
Salt soluble proteins were isolated and analysed as reported previously (Drinic et al. MNL 70:71-72, 1996; Konstantinov et al. MNL70:72-73, 1996; Mladenovic-Drinic and Konstantinov, In "Genetics and exploitation of heterosis in crops", Int. Symp. Mexico City, Mexico, 1997, pp. 94 - 95). Association among 15 inbred lines analysed has been determined from cluster analysis based on protein marker data. The UPGMA clustering method was used for hierarchical clustering and the necessary computations were performed using the NTSYS-pc program.
The protein based dendrogram for 15 analysed inbred lines, consisting of three major groups, is presented in Fig. 1. The first group (Cluster 1) consists of inbred lines derived from or related to BSSS germplasm which clustered in the protein study; the second group (Cluster 2) belonging to Lancaster germplasm inbreds clustered in the protein study; and the third group (Cluster 3) is two public French inbred lines, F2 and F7 (Fig. 1).
Figure 1. Dendrogram for fifteen maize inbred lines based on cluster analysis (UPGMA) of genetic distances from embryo salt soluble protein data.
It is obvious from subdivisions that further break outs are very largely according to pedigree background. Within the BSSS group, B73 and B84, derived from advanced cycles of the recurrent selection program of Iowa Stiff Stalk Synthetic, clustered separately from sterile versions of B73 genotype (B73 Sbms) and B73M. The third subdivision consists of A632 with ZPL362. Inbreds ZPL326 and ZPL2217 were loosely aggregated with B73 and A632 related lines. Within the Lancaster group of inbreds association in two subdivisions of related lines has been obtained; lines ZPL385 and Mo17 clustering together in one subgroup, while ZPL395 and its progenitor ZPL412 were in another.
Grouping of inbreds revealed by the present analysis generally agreed
with the pedigrees of these lines. There is a major split between Stiff
Stalk and non-Stiff stalk pedigreed inbreds. Therefore results presented
support our suggestion that embryo salt soluble proteins provided association
of inbred lines that largely concur with expectations based upon pedigree
data, and are good candidates for discrimination between maize genotypes.
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