GENETIC STUDIES ON ISOZYME PATTERNS IN TR1TICUM AEST1VUM L.

Abstract

The tribe Triticeae includes three important cereals namely wheat, rye and barley and their wild relatives. Available wheat cultivars have limited genetic variability for resistance to insects, pests and diseases. They also lack tolerance to salinity, drought and other abiotic stresses. In the light og growing evidence of the limited and narrowing genetic pool of advanced wheal cultivars, research on the genetic resources of wild relatives of cultivated wheats becomes increasingly important. Present studies were undertaken with aim to evaluate variability of isoperoxidases and isoainylascs in different tissues of cultivated wheat and its related species. Determination of the chromosomal locations of genes controlling these isozymes was also carried out. The ultimate aim of the studies was to establish biochemical marker(s) characterizing genetic resistance. Current work is an indicative of homology of isoperoxidases and isoamylases at various ploidy levels of wild and cultivated wheats and their relatives. However, differences in relative mobility and absence or presence of certain bands had been noticed among hexaploid, tetraploid and diploid wheats and Aegilops. Results revealed the presence of certain isoperoxidases and isoamylases in Aegilops species which were absent in most of hexaploid wheal accessions. These isozymes could be used to differentiate species of Triticum. Comparison of hexaploid wheat isozymes with progenitors exhibited the presence of certain common bands between diploid, tetraploid and hexaploid species which is an indicative of the contrioution of the respective genomes to hexaploid wheat. Appearance of bands at similar sites in synthetic hexaploid wheat as of ‘CS’ strengthen the evidence about ibe origin of their genome. Variation observed for few bandsbeiwccn natural wheats and synthetic wheat exploited for the improvement of bread wheat. Amphiploid T. aeslivuni - Ae. ovoia exhibited the qualitative pattern of both parents, however, specific band of Ae. ovata had also been noticed. Aneuploid lines of T. aesiivum L. cv. ‘Chinese Spring’ alongwith its disomic control (2n = 6x=42; AABBDD) were utilized lo locate the genes for leaf and root isoperoxidases and isoainylases. Analysis of available nullisomic-tetrasomic lines for chromosomes of group I to 7 of the three genomes in different combinations implicated the involvement of IAS, IBS, 6BL, 7AS, 7AL and 7DS in the synthesis of leaf peroxidases. Homeologous chromosomes 6BS, 6DS and 7AL, 7DL are responsible for the synthesis of root isopcroxidasc. Present studies, by using CS/rye additional lines revealed that grain isoperoxidases of rye are related to chromosome 1 and 7 whereas root peroxidases showed the presence of rye bands cn additional line carrying chromosome 2R and 6R. The zymogram of grain peroxidase of barley indicated the involvement of chromosome 2H. 5H and 6H in the synthesis of grain peroxidases. As far as root peroxidases are concerned results showed the involvement of 2H and 7H. The localization of genes for leaf and root peroxidases on group 1, 6 and 7 genome of wheat and 1R, 6R and 7R of rye is an evidence of homeology between wheat and rye chromosomes. Zymogram analysis of nullisomic, tetrasomic and ditelosomic aneuploid genotypes of wheat cultivar ‘Chinese Spring’ indicated the possible location for the synthesis of leaf isoamylases on 6DS, 7AL and 7DL. Results of root isoamylases demonstrated the involvement of chromosomes IBS, 6BS, 6BL, 6DS and 6DL in the synthesis. The banding profile of CS/rye additional lines suggested the location of genes for leaf amylases on IR, 2R, 3R, 6R and 7P in three different tissues of rye. The studies on CS/barley addition lines exhibited the involvement of 2H, 7H and 5H chromosomes in the synthesis of grain and root amylases respectively. Isoperoxidase patterns of flag leaves have been investigated in diploid, tetraploid and hexaploid wheats and seventeen species of Aegilops. Most of Aegilops species had been screened previously for resistance against karnal bunt (Tilletia indied). Several were highly resistant to the pathogen. T. aestivum lacks genetic resistance. The study was further extended to establish biochemical marker(s) characterizing genetic resistance. In all 44 isozymes were determined, many of them were common in wild and cultivated species. Species of marker specificity belonged to Ae. cylindrica, Ae. ovata, Ae. biuncialis, Ae. crass a. Ae. juvenalis, Ae. vavilovi and Ae. triaristata. The present investigation highlights the peroxidase isozyme variation and practical diagnostic usage of isoperoxidases in wheat improvement.