Effects of some systemic fungicides on the chiasma frequencies in Hordeum vulgare.

Abstract

Modern agriculture has introduced a large number of pesticides into the environment. Some of these were demonstrated to exert toxic influences on various non-target organisms including plants (Mrak 1969 , Epstein andLegator 1971). In higher plants there were reported on the pesticide influences on mitosis and meiosis (Wuu andGrant 1966, 1967). However , it was not investigated whether or not the recombinant source of variation in meiosis was affected . To enquire such a possibility four systemic fungicides are presently tested in Hordeum vulgare for possible impact on chiasma frequency which is not only an indicator of the degree of recombination but also a demonstrable parameter carrying a wide range of implications (Rees and Thompson 1956, Dowrick 1957, Rees and Jones 1976. Since several agricultural chemicals were reported to be mutagenic (Epstein and Legator 1971, Panda andSharma 1979), sodium azide , a known mutagen has also been tested for comparison. Material and methodsSolutions of different strengths of thiabendazole, fuberidazole, carboxin, oxycarboxin and sodium azide were prepared in a phosphate buffer (0.1M) adjusted to pH 7. Traces of acetone were added for facilitating solubility when ever necessary. Seeds of a cultivated barley, Hordeum vulgare C. V. 292 (2n=14), were soaked in the distilled water for 15hrs, and treated in the different test solu tions for 6 hrs. This duration approximately corresponded with the mid-S phase of the initial mitosis (Khalatkar 1976, Panda andSharma 1980) in the seeds. After a thorough wash the seeds were germinated in petriplates and a week-old seedlings were transplanted to the field. During the flowering season first spikes from five different plants were fixed in acetic alcohol and florets were squashed in aceto carmine. Chiasma frequencies were determined from at least 30-50 metaphases from these squash preparations representing the five plants (Bennett and Rees 1970). Negative controls were maintained, separately for experiments with each test com pounds, in the buffer or acetonised buffer. Percentage of reduction in the chiasma frequency was measured as depression index. The work was triplicated. ObservationsThe number of chiasmata per cell ranged between 12-27 in the controls, 14 and

Meiosis evolves: adaptation to external and internal environments

“…Between the temperature extremes at which meiosis fails altogether, environmental variation also causes variation in crossover frequency, which has important implications for models of the evolution of recombination as well as for population genetics and breeding (Otto & Michalakis, 1998;Otto & Barton, 2001;Marais & Charlesworth, 2003;Roze & Barton, 2006). The range of biotic and abiotic environmental factors known to affect crossover rates is remarkably broad and includes temperature, nutrient availability, fungicide application, pathogen attack, droughtand, in grasshoppers, even swarming (Grant, 1952;Law, 1963;Nolte, 1968;Bennett & Rees, 1970;Fedak, 1973;Sharma et al, 1983;Choudhary & Sajid, 1986;De Storme & Geelen, 2014). This begs the question why so many diverse environmental inputs affect meiosis.…”

Anthropogenic Impacts on Meiosis in Plants

“…The mean chiasma frequency in each of three cultivars was significantly reduced to 2–4% lower than the control. A later study in the same species showed that the systemic fungicides fuberidazole, carboxin, and oxycarboxin (but not thiabendazole) all significantly reduced chiasma frequency ( Sharma et al, 1983 ). Carboxin and oxycarboxin has an effect even at the lowest concentration tested.…”