1022-7954/03/3912- $25.00 © 2003 MAIK “Nauka /Interperiodica” 1405 Russian Journal of Genetics, Vol. 39, No. 12, 2003, pp. 1405–1411. Translated from Genetika, Vol. 39, No. 12, 2003, pp. 1656–1663. Original Russian Text Copyright © 2003 by Gordeeva, Badaeva, Budashkina, Omel’yanchuk. INTRODUCTION Since common wheat is a polyploid organism, nulli- somic, monosomic, and telocentric series substantially simplify genetic analysis and provide possibilities of assigning genes of interest to particular chromosomes, establishing the number of genes controlling the devel- opment of a particular trait, or studying the effects of gene interplay or allelic interactions. Owing to cytological stability and distinct pheno- typic differences, nullisomic wheat lines are most con- venient for genetic analysis. All gametes lack one par- ticular chromosome in nullisomics, and self-pollination yields uniformly nullisomic progeny in the case of complete chromosome conjugation in meiosis. How- ever, most nullisomic lines are sterile and, conse- quently, difficult to maintain. Only nullisomy for chro- mosome 7B may be maintained in a stable line, whereas it is virtually impossible to obtain any progeny by self-pollination of other nullisomics. Hence, self- pollination of monosomic lines is commonly used to obtain nullisomics [1]. Sears [1] was first to obtain and to describe mono- somic wheat lines in 1954 [1]. Monosomic lines, which each lack a particular chromosome, express the nor- mal phenotype under favorable growth conditions. Of all monosomic series, only two lines, mono-A5 and mono-5D, phenotypically differ from disomics. In plants monosomic for chromosome 5A, the spike is long speltoid, rather than dense clavate, and flower and grain numbers per spiklet are substantially reduced. Plants monosomic for chromosome 5D have a lower maturity rate and come into ear 7–12 days later on stan- dard spring seeding. It is for this reason that speltoids are the best studied wheat mutants [2]. As clearly dem- onstrated by monosomic analysis, the long arm of chro- mosome 5A has a locus whose dominant allele Q sup- presses development of speltoid characters, including loose spike, harsh glume, and long thin culm. Omel’yanchuk et al. [3] studied variation of prog- eny in a wheat somaclonal line (SK) and demonstrated that the speltoid phenotype and awnless spike are caused by monosomy 5A. In further analysis, awned plants were observed in the progeny of some speltoid plants, which were selected from a mono-5A soma- clonal wheat line (2n = 41 = 20II + I) and reproduced by self-pollination for six generations (SK6). The objective of this work was to study the cause of gener- ation of fertile awned plants. MATERIALS AND METHODS For callus induction, we used immature embryos of isogenic common wheat line ANK-12, which was obtained by S.F. Kovalev by crossing a line (5 cycles of strong self-pollination under insulators) of cultivar Novosibirskaya 67 with cultivar Norin 10, which car- ried the Rht2 gene (reduced plant height), and subse- quent backcrossing (8 cycles) with cultivar Novosibir- skaya 67 [3]. We analyzed the progeny of a speltoid plant result- ing from self-pollination of plants (first generation) regenerated from callus of the isogenic common wheat line. A plant with speltoid spikes was observed in the progeny (total 43 plants) of a second-generation regen- erant (SK2). To obtain the third (SK3) and further gen- erations, we used only seeds from awnless (sp) or awned (a/sp) speltoid plants carrying 41 chromosomes. To study meiosis, spikes were fixed with Newcomer’s The Effect of Substitution of Chromosome 5A with an Extra Chromosome 5B in the Progeny of a Somaclonal Common Wheat Line Monosomic for 5A E. I. Gordeeva 1 , E. D. Badaeva 2 , E. B. Budashkina 1 , and N. A. Omel’yanchuk 1 1 Institute of Cytology and Genetics, Russian Academy of Sciences, Novosibirsk, 630090 Russia 2 Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, 119991 Russia; fax: (3832)33-12-78; e-mail: bud@bionet.nsc.ru Received February 10, 2003; in final form, June 16, 2003 Abstract—Cytogenetic analysis was employed in studying the cause of generation of fertile awned forms in the progeny of plants, which were selected from a speltoid somaclonal wheat line monosomic for chromosome 5A (2n = 41 = 20II + I), had speltoid spikes, and were reproduced by self pollination. On cytogenetic and genetic evidence, chromosome 5A was eliminated and the copy number of chromosome 5B increased in the plants examined. The appearance of an extra chromosome 5B is probably caused by nondisjunction of bivalent 5B in the presence of a telocentric originating from the long arm of chromosome 5A. A difference in meiotic segre- gation was observed for univalent chromosomes 5A and 5B. PLANT GENETICS