GrainGenes
A Database for Triticeae and Avena
Finch, pp. 2-3
II. 1. Deficiency of 6L in diploid barley.
R. A. Finch, Plant Breeding Institute, Maris Lane, Trumpington, Cambridge, England. "R"
A diploid plant with one chromosome 6 lacking its whole long arm (2n=13+6S) in all root and shoot cells studied survived in our glasshouses for 7 months and died after setting 2 seeds, both of which gave normal (2n=14) seedlings. In 5 root tip metaphases, the relative lengths of identifiable chromosomes (6S, 6, 7 and 5) compared with one another and chromosomes 1-4 showed that only chromosome 6S was abnormal (Fig. 1) and no sign of interchange was seen in MI pollen mother cells (pmc's). The plant was thus a monotelodisomic (Kimber and Sears, 1968). Viable large deficiencies are rare in diploid plants and animals (see Finch, 1983) and this plant was the only deficient diploid barley known to me apart from one where 2n=13 + acrocentric which died at coleoptile stage (Tsuchiya and Shahla, 1982; Tsuchiya, pers. comm.). For deficiency to be found so rarely in a species as well studied as barley suggests that it is truly diploid.
The plant arose from a selfed chromosome 4 monotelotrisomic (2n=14+ telo 4) derived from Shin Ebisu 16 after crosses with Sultan and Paavo line P-4 (Finch, 1983). It was dwarf, many-tillered and grew slowly. Many leaves and spikes were deformed, palea were often awned and fused to lemmas and many spikelets had much-branched rudimentary florets and no normal organs.
The deficiency was seen in all somatic metaphases studied in 2 seminal roots, 3 roots taken when spikes were near meiosis and anthers and ovules at or shortly after meiosis. It was also seen in all meiocytes at stages where chromosomes could be counted. Meiosis was regular at all stages in pmc's and where seen in embryo sac mother cells at first prophase and second division. All of a sample of 20 MI pmc's had 1 asymmetric bivalent with 1 chiasma plus 6 symmetric bivalents with 1-3 chiasmata. There were 13.30+0.26 (range 11-16) chiasmata and 1-3 rod bivalents per pmc. Male and female meiosis were concurrent in most florets.
No cytological instability was seen in any tissue, but the final tapetal mitosis was asynchronous and gave many mononucleate and binucleate cells and in one sample, 4.6 per cent of pollen grains had a micronucleus just after the tetrad stage. Despite the relative regularity of its chromosome behaviour, the plant was highly sterile even in normal florets pollinated with Sultan.
Unlike its ancestors, the monotelodisomic showed some similarity in its spikes to the recessive multiflorous phenotype caused by the mul2 allele on chromosome 6 (Tsuchiya and Haus, 1971). The chromosome 6 centromere is not mapped but the Mu12 locus may have been hemizygous in this plant and, if so, the multiflorous phenotype may have been due to hemizygosity of the normal Mu12 allele, which would suggest that the mul2 "allele" is really a deletion at the Mul2 locus. This would be plausible if Mul2/mul2 heterozygotes also showed some sign of the multiflorous phenotype. However, Walker et al. (1963) do not mention heterozygous expression of mul2.
References:
Finch, R. A. 1983. Viable long-arm deficiency in diploid barley. Heredity
(in press).
Kimber, G. and E. R. Sears. 1968. Nomenclature for the description of aneuploids in the Triticinae. Proc. 3rd Int. iJheat Genet. Symp., Canberra (eds K. K. Finlay and K. W. Shepherd):468-473.
Tsuchiya, T. and T. E. Haus. 1971. Multiflorous 2. Barley Genet. Newsl. 1:154.
Tsuchiya, T. and A. Shahla. 1982. Chromosome constitutions in the progenies of haploid initiator mutant, hap/hap homozygote in barley. Barley Genet. Newsl. 12:34.
Walker, G.W.R., J. Dietrich, R. Miller and K. Kasha. 1963. Recent barley mutants and their linkages II. Genetic data for further mutants. Can. J. Genet. Cytol. 5:200-219.