INTERNATIONAL JOURNAL OF RESEARCH CULTURE SOCIETY Gamma rays and EMS induced chromosomal abnormalities and pollen fertility in Brassica campestris (L.) genotypes

Krishna Gopal, Shukla
2017 unpublished
INTRODUCTION: Crop improvement is a key route to ensuring continued benefits arising from food and plant products. Wide range of genetic, biochemical and metabolic variation needs to be generated for effective crop improvement. With the discovery of ionizing and chemical mutagens a new field of science known as "mutation breeding" was developed. These mutagens may cause genetic changes in an organism, break the linkages and produce many new promising traits for the improvement of crop plants.
more » ... t of crop plants. Induced mutations provide beneficial variations for practical plant breeding purpose. During the past seven decades, more than 2252 mutant varieties have been officially released in the world (Maluszynski, et al., 2000). 1 Khatri et al., (2005) 2 reported that gamma rays and EMS could be fruitfully applied to develop new varieties with high yield and other improved agronomic traits in Brassica juncea . Thus to administer successful mutagenesis, selection of efficient mutagen and treatment is a pre-requisite. Mutagens are the potent tool to create novel variation particularly in those crops with restricted or lack of genetic diversity. The cytological abnormality serves as the primary effect of phenotype variation. Degree of cytological aberration either in mitosis or meiosis is regarded as one of the dependable criteria to estimate the radio-sensitivity of the species and the effect of mutagens (Ignacimuthu, 1989). 3 Pollen sterility is also used for calculating the mutation index which is a good indicator to forecast the spectrum of genetic variability that can arise from the mutated sectors. Considering these researches attributes, the present investigation documents mutagenic effectiveness of gamma rays and EMS on chromosome biology of Brassica campestris (L.) genotypes T-9 and PT-303. MATERIALS AND METHODS: Two varieties of Brassica campetris (L.) T-9 and PT-303, physical mutagen (gamma rays) and chemical mutagen Ethyl Methane Sulphonate (EMS) were employed in the present study. The seeds of these varieties were procured from U.P. State seed corporation, Lucknow. The healthy seeds of T-9 and PT-303 were treated with gamma rays ( 25 KR, 35 KR and 45 KR) through 60Co source (at the dose rate of 1.8 KR/sec) done at National Botanical Research Institute (N.B.R.I. Lucknow, India) and three different doses/concentrations of EMS such as 0.3%, 0.6% and 0.9% in laboratory. Both these treatments were done to create genetic variability for selection of desirable genotypes. After each treatment the irradiated seeds were sown in experimental field along with their suitable control counterparts for pollen studies. However, for mitotic studies treated seeds were grown in petriplates (lined with moist filter paper) along with their controls. The healthy root tips were fixed in carnoy's fixative (1:3 glacial acetic acid + alcohol), preserved in 70 % alcohol and stained in 2 % acetocarmine. For the pollen studies, floral buds of appropriate size were collected and stained in 2 % acetocarmine. Photomicrographs were taken and analyzed using Nikon image capturing system. Mitotic indices and percentages of abnormally dividing cells were calculated. Different types of chromosomal abnormalities such as laggards, fragments, bridges etc. were detected from the desired preparations. They were detected from metaphase; anaphase and telophase stages of mitosis and data were recorded and analyzed statistically. Abstract: Mutagenesis has come up with a hope as an efficient tool for creating genetic variability and boosting up of characters under consideration. Degree of cytological aberration either in mitosis or meiosis is regarded as one of the dependable criteria to estimate the radio-sensitivity of the species and the effect of mutagens .With this view, to understand effect of various doses of gamma rays and EMS on the meristmatic root cells of two genotypes T-9 and PT-303 of Brassica campestris (L.) (2n=20), this work was undertaken. It was found to mutagens caused declining trends in mitotic indices with increasing doses/concentrations in both the cultivars. The percentages of abnormalities is directly proportional to doses/concentrations, abnormalities included stickiness, clumping, c-metaphase, laggard and bridges at anaphase and telophase were observed in dividing cells. The pollen fertility among all the mutagenic treatments shows gradual decreases with respect to the increase in concentrations. It may be attributed due to induced chromosomal aberration. The percentage of chromosomal aberrations observed in case of EMS treated set was higher than gamma rays treated sets suggesting that EMS could be successfully employed for creating novel genetic variability in oilseed Brassicas.
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