BGN 2: Selection of trisomic plants in chromosome 3-trisomic barley strains by means of esterase isozymes BARLEY GENETICS NEWSLETTER, VOL. 2, II. RESEARCH NOTES
Nielsen, pp. 62-64

II.22. Selection of trisomic plants in chromosome 3-trisomic barley strains by means of esterase isozymes.

Gunnar Nielsen. Agricultural Research Department, Danish AEC, Research Establishment Riso, Roskilde, Denmark, and AEC Plant Research Laboratory, Michigan State University, East Lansing, Michigan, U.S.A.

In progenies from trisomic barley plants only about 15 to 20 per cent are found to be trisomics, and the rest of the plants are normal diploids. For chromosome 3-trisomic plants, chromosome counting is the only safe method to use to distinguish trisomics from diploids, but it is a time consuming procedure. This report describes a safe and convenient method for selecting chromosome 3-trisomics, based on starch gel electrophoresis of a four-allele esterase system (locus Est-1) in barley leaves.

For localizing a gene on a chromosome by use of trisomics, the genetic background for the trisomic plants is not very important, provided the trisomics are homozygous for the gene which is allelic to the gene to be localized. Then plants heterozygous for the Est-1 alleles may be used. The gene-dosage effect of the esterase isozymes in trisomic barley has been used to localize the Est-1 locus on chromosome 3 (Nielsen and Frydenberg 1971). It is also possible to use the gene-dosage effect to select trisomic plants in a chromosome-3-trisomic strain, heterozygous for Est-1 alleles, but the method is based on a quantitative estimation of the band-intensity, which requires a perfect electrophoresis. Other difficulties arise from the fact, that Est-1 alleles have different levels of activity in different varieties, as seen on the relative intensity of the bands from heterozygotes (unpublished data). If a four-allele system is used, however, the selection of trisomic plants can be based on the number of bands and the quantitative estimation of the intensity can be avoided.

Among 120 kernels harvested on one of the three Est-1Ca/Al/Pr trisomic plants described by Nielsen and Frydenberg (1971b), 22 trisomics were found, six of which had the genotype Est-1Ca/Al/Pr. The numbers are in agreement with the expected ratios (one third of the trisomics are expected to be Ca/Al/Pr). Several spikes from the six three-allelic plants were pollinated by the variety Afghan I, which has a fourth Est-1 allele, designated Est-1Af, and the Est-1 types in the progeny from this cross are shown in Table 1, The segregation from self pollination of Est-1Ca/Al/Pr trisomics is shown in Table 2.

Table 1. Cross: Est-1Ca/Al/Pr female x Est-1Af male

Table 2. Self pollination of Est-1Ca/Al/Pr trisomics

Of the four possible three-allelic trisomic types, three (Af/Ca/Al, Af/Ca/Pr, and Af/Al/Pr) are obtained from the cross with Afghan I (Table 1) and one (Ca/Al/Pr) from the selfing (Table 2). These four Est-1 phenotypes are shown in Figure 1.

Figure 1. Diagram showing the four three-allelic trisomic Est-1 phenotypes, Af/Ca/Al, Af/Ca/Pr, Af/Al/Pr, and Ca/Al/Pr, as they appear after starch-gel electrophoresis. Only Est-1 bands are shown.

The plants with the gene to be localized is assumed to be homozygous for one of the four Est-1 alleles. This allele is absent in one of the four three-allelic trisomic types. This type is used for crossing. In the progeny of this cross, all the trisomics will show three electrophoretic Est-1 bands, the male parent band and two of the female parent bands. The diploids will show only two bands, the male parent band and one female parent band. If the male parent band is absent, the plant is a result of a self-pollination. This observation is used as a hybrid test.

A comparison of chromosome-counting and the Est-1 esterase methods for selecting trisomic plants is given below. (The calculation is based on an expected frequency of 15 to 20 per cent trisomics.)

Selecting trisomic plants for crossing:
Chromosome counting: 6 plants selected per 30-40 counted
Est-1 method:  6 plants selected per 90-120 analysed
 

Selecting Fl-plants:
Chromosome counting: 6 plants selected per 30-40 counted
Est-1 method:  6 plants selected per 30-40 analyzed (hybrid test included).

References:
Nielsen, Gunnar and Frydenberg, Ove. 1971a. Chromosome location of Est-1 by analyzing F1 trisomic plants. BGN 1:35-360

Nielsen, Gunnar and Frydenberg, Ove. 1971b. Chromosome localization of the esterase loci Est-1 and Est-2 in barley by means of trisomics. Hereditas 67 152-154.

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