| A very high frequency of nullisomics in selfed monosomic
population for chromosome 3A of T. aestivum var. Pb. C 591 B.C. JOSHI, Dalmir SINGH, B. LAL and Dhani RAM, Division of Genetics, Indian Agricultural Research Institute, New Delhi, India Chlorophyll synthetic gene (s) CSG3A has been located on chromosome 3A of T . aestivum var. Pb. C 591 by SINGH and JOSHI (1979), on the basis of the observation that nullisomic albina seedlings occur only in the monosomic line for chromosome 3A. An attempt was made to calculate frequencies of disomics, monosomics and nullisomics in this monosomic line of Pb. C 591. Three hundred to four hundred seeds, obtained from cytologically identified 3A monosomic plants, were grown every year in petri dishes. The number of green and albina seedlings were recorded for every plant progeny separately. Albina represented nullisomics (SINGH and JOSHI, 1979). All the green seedlings were transplanted in the field. At the time of maturity all the plants were harvested and threshed separately. The frequencies of disomics and monosomics were determined on the basis of segregating plant progenies for green and albina seedlings (only monosomic plants segregated). Data for eight years are given in Table 1. In all, two thousand eight hundred and fifty plants were sown during the span of eight years. It was observed that 343 were albina seedlings (12.03%) and 2507 were green plants which were transplanted in the field. Out of these 2507 plants, 1739 plants segregated for albina and green seedlings, representing monosomics and 768 produced only green seedlings representing disomics. Percentage for disomics, monosomics and nullisomics thus obtained was 27% (21)", 61% (20"+1') and 12% (20"), respectively. |
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