Effect of NMU and EMS on chromosomal behaviour of Lycopersicon esculentum Mill. during meiosis.

Abstract

Meiosis is complex process, which ensures the reduction of chromosomes number and genetic recombination through cytological phenomenon such as homologous chromosome pairing, formation and maintenance of chiasmata, disjunction of bivalents etc. (Kitada et al. 1983). The degree of meiotic abnormalities, being a dependable measure for estimating the effect of mutagen in the immediate generation, has been utilized by several workers (Grant and Harney 1960, Razarietelva et al. 1970, Kuvcera 1972, Mashnenkov and Golubouskaya 1980, Salnikova and Dosmailova 1979, Verma and Raina 1982 to ascertain the mutagenecity of some chemical mutagens on different crop plants. The present study has been undertaken to assess the effect of NMU and EMS on the meiotic behaviour of CO.2 and Pusa Ruby. Materials and methodsA stock of plants were raised from selfed seeds collected from a single plant of CO.2 and Pusa Ruby-two cultivars of Lycopersicon esculentum Mill. The plants were grown under uniform experimental conditions in the botanical garden of the Bharathidasan University, Tiruchy.For each concentration, three samples of 100 seeds each were taken, along with the control. The concentrations of EMS and NMU were prepared in sodium phosphate buffer solution pH 7.0. The concentrations of EMS used were 10mM, 20mM, 30mM, 40mM and 50mM., while that of NMU ranged from 1mM to 5mM in 1mM increments. Since the imbibition period was 8 hours, the seeds were soaked in distilled water for 8 hours and in mutagens for 4 hours. The treated seeds were then washed in running water for 30 minutes and were sown in field along with controls.At the time of blooming, flower buds of appropriate age were collected at random from 10 M, plants per treatment and fixed in Carnoy's fluid (Swaminathan et al. 1954). Meiosis was studied in squashes of 500 pollen mother cells (PMCs) of each stage. The slides permanet ly fixed using the butyl alcohol schedule of Bhaduri and Ghosh (1954). Pollen sterility was estimated per 2,000 pollen grains for each plant on the basis of stainability with Alexander's stain (1969). Five flowers were selected from each plant for estimating pollen fertility. A total of 20,000 pollen grains were scored per treatment. Results and discussionIn the controls, meiosis at metaphase I was normal with 12 bivalents (Fig. 1), of which an average 8-10 were ring bivalents and the remainders were rods. At diakinesis, the frequency of chiasmata per bivalent was 1.8 in CO.2 and 1.94 in Pusa Ruby.Meiosis of plants in the M1 generation was highly irregular (Tables 1, 2) and the abnor malites (Figs. 2-6) observed in both varieties were similar. Hence a common description is