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Characterization of pear species and cultivars using isozyme polymorphism

Sharifani, M., Jackson, J.F.
Acta horticulturae 2002 no.587 pp. 269-278
Dacryodes edulis, Pyrus, acetates, alcohol dehydrogenase, alleles, buffers, computer software, cultivars, enzyme activity, genetic variation, glucose, glutamate dehydrogenase, heterozygosity, isocitrate dehydrogenase, isozymes, leaves, loci, pH, pears, phenolic compounds, phosphoglucomutase, pollen, sodium phosphate
Self-incompatibility and heterozygosity in the genus Pyrus has led to high genetic diversity in this genus. Codominant isozyme markers was applied for better identification of this genus. As there was a large amount of phenolic compounds in pear leaf, working with the leaf was a problem for isozyme extraction. Thus pollen instead of leaf was used for isozyme extraction. This was due to its higher enzyme activity, easier extraction and simpler isozyme banding pattern. Fourteen pear cultivars and 11 species were selected. These pears belonged to four groups of West Asian, East Asian (Japanese), European and North African pear. Two running buffers including sodium phosphate pH 7 and Tris malate pH 7.8 were used for this study. The first buffer was used for Alcohol Dehydrogenase (ADH) and Phosphoglucomutase (PGM). The second buffer was applied for Glucose Phosphate Isomerase (GPI), Glutamate Dehydrogenase (GDH) and Isocitrate Dehydrogenase (IDH). Cellogel acetate sheet 200 μm thick was used for this study. The similarity matrix was calculated in a Macro comparison program using an Excel Macintosh software. Results showed that PGM isozyme system had four zones of activity representing four separate loci. PGM-3 and PGM-4 showed better resolution than the two other loci. We obtained 9 groups of pears based on the structure of two PGM-3 and PGM-4 contained on 3 alleles. GPI showed a higher range of variation within pear cultivars and species. A category of GPI banding patterns divided the pears into 10 groups. Five types of IDH banding patterns were obtained for different pears. Three different ADH-2 banding patterns draw up the pears into 3 groups. In the ADH system two anadoic bands revealed for Choujuurou and Housui were different from the other pears. Results obtained from the similarity matrix of pears showed significant relatedness among some pear species and cultivars. The close similarity of P. gharbiana with P. pyraster suggests the relatedness of these two pears. GPI and PGM revealed more discriminative characterization of pears, which in turn were useful for identification of narrow genetic differences.