| Heading date in the aneuploid lines of wheat and cause
of variation B.C. JOSHI and D. SINGH Division of Genetics, Indian Agricultural Research Institute New Delhi, India. We have observed that the flowering time of disomic plants (2n=42), in different monosomic lines in the aneuploid series of wheat variety Chinese Spring (SEARS 1954) and Pb. C591 (SWAMINATHAN et al. 1968) is significantly different. Within a line the disomic and the monosomic plants (2n=41) flower at the same time. Since the disomic plants of all the lines carry a full complement of chromosomes it is expected that they should not differ from each other in the expression of this character. Differences in the monosomic plants, as compared to control, could be expected due to the deficiency of a chromosome. In this note we report the variation in disomic plants belonging to different monosomic lines for the onset of flowering and analyse source of this variation. Data on mean number of days for flowering in the monosomic and the disomic plants of 20 aneuploid lines of Pb.C591 were recorded. It was observed that in all the lines the monosomic and the disomic plants did not differ significantly in flowering date from each other and, therefore, the data of individual lines for flowering date was pooled up to obtain mean values (Table 1). The data show that monosomic and the disomic progenies of the line derived from mono-5B, which are earliest in flowering, head after 85 days of sowing and those of line 6B take 91 days to flower. Other lines fall in between this range. What is the source of variation of disomic derivatives of monosomic lines? The time period available for identifying all the aneuploid lines of Chinese Spring and Pb. C591, in addition to other concomitant cytological analyses, is very short and the personnel are few, as such the identification of monosomic plants is started when the very first plant comes to analyzable stage. Due to this reason any spontaneous mutation for earliness would be selected in some lines. The derivatives of these lines then would become early as compared to other lines. Similarly, there is a possibility of selecting late mutations in some lines because it is attempted to prolong the time period of analysis of meiotic chromosomes and monosomic plants in some lines are identified late in the season. KUSPIRA & UNRAU (1957) have shown, using substitution lines of Chinese Spring, that major genes for earliness are located on several chromosomes in the three varieties studied by them. Spontaneous mutations for this character are thus expected to occur in many aneuploid lines. Since the genes on the univalent of the monosomic plants are present in a hemizygous state, it is to be expected that the expression of mutations of genes on the univalent will be facilitated. This could effect homozygosity for newly arisen mutants. Literature Cited KUSPIRA, J. & J. UNRAU 1957. Genetic analyses of certain characters in common wheat using whole chromosome substitution lines. Can. J. Pl. Sci., 37 : 300-326. SEARS, E.R. 1954. The aneuploids of common wheat. Research Bull. 572, Univ. of Missouri pp. 1-59. SWAMINATHAN, M.S., V.L. CHOPRA, B.C. JOSHI & D. SINGH 1968. Development of a monosomic series in an Indian wheat and isolation of nullisomic lines. Wheat Inf. Serv., 27 : 19-20. |