BGN 2: Tertiary trisomics balanced for ms1, for ac2 and for both ms1 and ac2 BARLEY GENETICS NEWSLETTER, VOL. 2, II. RESEARCH NOTES
Ramage and Paluska, pp. 68-69

II.25. Tertiary trisomics balanced for ms1, for ac2 and for both ms1 and ac2.

R. T. Ramage and Michele Paluska. Plant Science Division, ARS, U.S.D.A., Agronomy and Plant Genetics Department, University of Arizona, Tucson, Arizona 85721.

Last year (BGN 1:38-40) we reported that the translocated chromosomes T51b and T51c carried both the ms1 (male sterile) and ac2 (albino seedling) loci The ms1 locus is carried on the centromere segments of chromosome 5 and the ac2 locus is carried on the translocated segments of chromosome 1. Tertiary trisomics for chromosome T51b and T51c can be established that are balanced for ms1, for ac2 and for both ms1 and ac2.

Tertiary trisomics for chromosome T51b and T51c that are balanced for ms1 were established several years ago and have been placed in the World Collection of Balanced Tertiary Trisomics (BGN 1:80). This report is to announce the establishment of tertiary trisomics for chromosomes T51b and T51c that are balanced for ac2 and for both ms1 and ac2. These four BTT's are being added to the World Collection of Balanced Tertiary Trisomics (BGN 2:135). Limited amounts of seed are available upon request.

The BTT's described in this report were obtained from crosses of BTT 51b ms1 and BTT 51c ms1 females with BTT 17c ac2 and BTT 61a ac2 males. F1 trisomic plants were identified cytologically. They should have had a diploid complement that was heterozygous Ms1 ms1 for chromosome 5 and Ac2 ac2 for chromosome 1. The extra chromosome, T51b or T51c, carried both dominant alleles Ms1 and Ac2.

F2 phenotypes of the progenies for F1 trisomic plants were grown. The diploid portion of the F2 progenies were expected to be in the typical dihybrid ratio: 9 green, male fertile;3 green, male sterile: 4 albinos. The phenotypes of the trisomic portion would be all green and male fertile because of the presence of the Ac2 and Ms1 alleles on the extra chromosomes.

The genotypes of the trisomic portion of the F2 progenies were expected to be in a 1 Ac2 Ac2 Ac2:Ac2 Ac2 ac2 : 1 Ac2 ac2 ac2 ratio. The albino seedling genotypes were determined by growing F3 progenies in a sand bench. Trisomics with an Ac2 ac2 ac2 genotype should have been BTT's for ac2. Their male sterile genotypes should have been in a 1 Ms1 Ms1 Ms1:2 Ms1 Ms1 ms1:l Ms1 ms1 ms1 ratio. The male sterile genotypes were determined by crossing trisomic plants from the F3 progenies as males onto diploid Ac2 ac2 ms1 ms1 females. All testcross progenies were expected to segregate 1 green : 1 albino seedling. Testcross progenies from Ms1 Ms1 Ms1 trisomics would be all male fertile, those from Ms1 Ms1 ms1 trisomics would segregate 1 male fertile:1 male sterile, and those from Ms1 ms1 ms1 trisomics would be all male sterile.

Ratios from testcrosses and from selfed progenies of the BTT's are given in Table 1.

Table 1. Ratios from testcrosses and selfed progenies of BTT 51b and BTT 51c.

Trisomics with the Ac2 ac2 ac2 Ms1 Ms1 Ms1 genotype are BTT's for ac2 and trisomics with the Ac2 ac2 ac2 Ms1 ms1 ms1 genotype are BTT's for both ac2 and ms1. BTT's with these genotypes were also obtained from F3 progenies of F2 trisomics of the Ac2 ac2 ac2 Ms1 Ms1 Ms1 genotype.

Many of the testcross progenies contained an excess of green seedlings. As only one trisomic testcross plant has been observed, pollen transmission of the extra chromosome can be eliminated as the cause of the excess of green seedlings. The cause must be within the Ac2 ac2 ms1 ms1  diploids that were used as female parents of the testcrosses. A mechanism such as gametic lethality or megaspore competition may be involved. Perhaps such mechanisms can be exploited in the commercial production of male sterile plants to be used as female parents of hybrids.

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