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Development of a monosomic series in an Indian wheat
and isolation of nullisomic lines M. S. SWAMINATHAN, V. L. CHOPRA, B. C. JOSHI and D. SINGH Division of Genetics, Indian Agricultural Research Institute, New Delhi, India The series of twenty one monosomic lines in the wheat variety Chinese Spring, developed by Dr E.R. SEARS, has greatly helped in advancing our understanding the genetics of the hexaploid bread wheat. Utilizing the monosomics of Chinese Spring, the Canadian workers have transferred the monosomic condition to other wheat varieties (UNRAU and MCGINNIS 1958). This report deals with the production of a complete series of monosomic lines in an Indian wheat variety Pb. C591 and the isolation of several nullisomic lines in it. Pb. C591 is a fully bearded vairiety susceptible to all the three rusts. The purpose of producing chromosome deficient lines in this variety is to utilise them for the study of quantitative traits (JOSHI and KUMAR 1967, JOSHI and SINGH 1968) and to locate genes for rust resistance on specific chromosomes. In such studies the susceptible genetic background of Pb. C591 will be helpful in revealing the critical chromosome of the donor variety by the resistant reaction caused by the gene or genes introduced by such a chromosome. All the 21 monosomic lines of the variety Chiriese Spiring, obtained from Dr. E.R. SEARS, were crossed as female parent with Pb. C591. The monosomic F1's (2n=41) in each of the 21 lines were identified cytologically and again crossed as female with Pb. C591. This backcrossing programme of the monosomic hybrids with Pb. C591 was repeated till the sixth backcross generation, ensuring that all chromosomes in the 21 monosomic series are from Pb. C591. All the chromosome deficient lines of Pb. C591 are morphologically similar to the parent variety. It is interesting to report that in the sixth backcross generation of mono 5A x Pb. C591, all the 45 plants were monosomics and no disomes were obtained. These plants, in the absence of chromosome 5A on which the speltoid suppressor gene Q is located, were easily identified phenotypically as 'speltoids'. From among the aneuploid series of Pb. C591, 14 different nullisomic lines (2n=40) have been isolated. The morphological characteristics of these nullisomics are given in Table 1. All the 14 nullisomics of Pb. C591, with exception of nulli 1D, are dwarf, weak, thin stemmed and thin leaved and straggling plants. Nulli 1D possesses medium broad leaves and stem. Nulli 5A and 6B have suppressed awning whereas all other nullisomes are fully bearded like the disome. This suggests that factors for awning, in Pb. C591, are located on chromosomes 5A and 6B. All the nullisomes isolated by us, except nulli 5B, seem to possess good female fertility because in all cases where adequate pollen was available the seed setting was fairly good. Meiotic metaphase I in nulli 5B of Pb. C591 shows multivalent formation, characteristic of chromosome 5B deficient plants of Chinese Spring (RILEY and CHAPMAN 1958, SEARS and OKAMOTO 1958). Literature JOSHI, B.C. and S. KUMAR 1967. Indian J. Genet. 27 : 86-89. JOSHI, B.C. and D. SINGH 1968. Indian J. Genet. 28 (1), In press. RILEY, R. and V. CHAPMAN 1958. Nature. London 182 : 713-715. SEARS, E.R. and M. OKAMOTO 1958. Proc. Tenth Int. Congr. Genet. 2 : 258-259. UNRAU, J. and R.C. MCGINNIS 1958. Proc. Genet. Soc. Canada 3 : 14-24. (Received June 30, 1968) |