Leaf extracts of Citrus growing in Cheju island were analyzed by starch gel electrophoresis for isozymes of phosphoglucose isomerase(PGI), phosphoglucomutase (PGM), isocitrate dehydrogenase(IDH), glutamate oxaloacetate transaminase(GOT) and malate dehydrogenase(MDH). The possibility of using the isozymes for the identification of nucellar and zygotic seedlings was examined. The results obtained are summarized as follows:
1. PGI activity was detected in three zones on the gel, the middle of which was specified by a gene named Pgi-1. PGM and IDH activity appeared in a single region, suggesting that these isozymes are controlled by a single gene, Pgm and Idly respectively. Zymograms of GOT and MDH were interpreted to be controlled by two genes Got-1 and -2, and Mdh-1 and -2, respectively. With alleles assigned to each gene, the genotypes of the isozymes were determined for each Citrus spp or cvs growing in Gheju. Some isozymes of GOT-2 not fully explained by the assigned alleles, were described by their phenotypes.
2. Three alleles, M and I of Mdh-1, and K of Mdh-2, were additionally assigned in this study. C. junos has a unique genotype of Mdh-1, MM, and more than half of Citrus spp native to Cheju island have M allele.
3. In the progeny of monoembryonic C. iyo x Bvungkyool , genes tested segregated as expected with the exception of Pgm (p$lt;0.001), and the segregation was independent of each gene except for Got-1/Pgm pair (p$lt;0.05).
4. The efficiency of isozymes as genetic markers was calculated in distinguishing the zygotic orignin from the nucellar for 253 possible cross combinations of 23 Citrus spp or cvs. For the 74 pairs, all zygotic seedlings were considered to be identified by a single enzyme system analysis.
5. The gene segregation were detected in the young zygotic plantlets obtained by the aseptic culture of embryos from C, natsudaidai artificially pollinated with Poncirus trifoliata. This result indicates that the isozyme analysis can be applied to the breeding program of embryoculture.
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