Use of enzyme molecular forms for tomato hybrid identification

Vodenicharova, M.S., Stoilova, Ts.B., Cholakova, N.I., Markova, M.D. and Ancheva, M.V. Institute of Genetics, Bulgarian Academy of Sciences, Sofia-III3, Bulgaria

One of the most important qualities tomato seeds for seed-production and sale must have is hybrid purity. The grow-out test for a hybrid purity estimation is based on information for morphological characteristics of the plants and has many disadvantages. The priorities of the electrophoretic method for FI hybrid purity analysis, as an alternative one, are indisputable and are applied at different cultivars by many authors (Wills et al., 1980; Tanksley et al., 1981: Smith et al., 1986; Orman et al., 1991). The use of isoenzymes for this purpose is based on the fact that they are direct products of gene expression and are independent of the environmental factors. This isoenzyme variability of the enzymes investigated is of importance too.

Sixty FI tomato hybrid seeds on the average (Kristi, Balkan, Standart 69, Maritsa 15, Maritsa 25, Hybrid 80, Hybrid 82 B) and the respective parental lines are analyzed. Electrophoretic division of the enzymes alcohol dehydrogenase (ADH, E.C.I.I.I.I.) and esterase (EST, E.C.3,I.I.I.), followed by histochemical coloring with modifications (Shaw et al., 1970) was applied. The method of vertical block electrophoresis in 7.5% PAGG at a continuous tris-EDTA-boric acid (pH 8.3) electrode buffer system was used.

Seeds of FI hybrids of fresh market tomatoes and parental lines were obtained from commercial breeders. On Fig. 1 the variability in the molecular forms of ADH and EST is shown. The established isoenzyme pattern of alcohol dehydrogenase is characterized by the fact that in the parental lines different alleles of one and the same locus (A) are expressed. If this locus is marked with A and its alleles are AI and A2, then the parental phenotypes for ADH will be AIAI and A2A2 and hybrid phenotypes -A1A2. All FI tomato hybrid seeds with phenotypes different from A1A2 are contaminations. Tanksley et al. (1981) also use allele variety of the alcohol dehydrogenase locus (Adh-1) for proving tomato hybrid purity but the phenotype manifestation of hybrid heterozygotes is different. The different methodological approach for Adh-I division is a probable reason for these results.

In the isoenzyme model of esterase (Fig. 2), manifestation of a locus, established both in the maternal and the paternal lines, is observed but with a higher activity of one of the alleles, expressed by the band with slow electrophoretic mobility in the paternal lines. In a hybrid zymograme a phenotype similar to the paternal one is observed but with still higher intensity of coloring of the slow-movable band.

The established isoenzyme molecular forms of the enzymes alcohol dehydrogenase and esterase can be used as genetic markers for tomato hybridity.

Figure 1. Zymograme of alcohol dehydrogenase (ADH) in F1 tomato hybrids: A1A1 - p1; A2A2 - p2; A1A2 - F1.

Figure 2. Zymograme of esterase (EST) in F1 tomato hybrids.

Literature cited

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Shaw, C.R., Prassad, R. 1970. Bioch. Genet. 4:297-320.
Smith, J.S.C., Wych, R.D. 1986. Seed Science and Technology 14:1-8.
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