1965 年 30 巻 2 号 p. 155-172
1. In spite of the many and varied reports on spontaneous mutations the factors responsible for their widespread occurrence in nature have not so far been clearly understood. Investigations carried out in the present study showed that decaying organic substances like compost, cowdung and oil cakes when present in high concentrations in the soil are capable of inducing mutations of different magnitudes. Chromosome changes induced by these substances and their possible role in the production of mutations in nature are discussed in this paper.
2. High concentrations of compost, cowdung and oil cake in sand exert a distinctly harmful effect as regards germination and growth. Very high concentrations of bassia oil cake (1 oil cake: 5 sand) inhibited germination. Though germination was observed in fresh cowdung the plants did not survive. No such inhibition in germination was observed in compost unmixed with sand. Lower concentrations of these substances have been found to be beneficial.
3. Cytological changes induced by compost, cowdung and oil cakes were almost similar. Breakage of chromosomes followed by reunion resutling in repatterning of chromosomes (translocation and inversion), chromosome doubling leading to polyploidy and spindle abnormalities resulting in the formation of aneuploid cells were commonly observed. Chromosome clumping, cytomixis, asynapsis, erosion of chromosomes etc. were some of the other abnormalities observed.
4. Quantitative analysis of the data showing the frequencies of the different abnormalities in the different treatments showed that the frequency of abnormalities increases with an increase in the concentration of the substances in the sand.
5. There is a gradual decrease in the percentage of aberrations with longer duration in compost, this relation being found in the pollen mother cells also. It is suggested that this decrease may possibly be due to the gradual fall in the content of nitrogen or other substances in compost causing these aberrations.
6. Cytological changes induced by a few fertilizers like ammonium sulphate, ammonium nitrate, ammonium phosphate and potassium chloride were studied with a view to comparing their effects with those of the organic manures used for the study. Abnormalities in cell division induced in the root tip cells of onion following treatment with these chemical fertilizers were almost similar to these observed in treatments with organic manures like compost, cowdung and oil cakes. The results of the studies appear to show that nitrogen, phosphorus and potassium can act as mutagenic factors in compost. The differences exhibited by compost, bassia oil cake and cowdung might probably be due to the variation in the relative concentrations of nitrogen, phosphorus and potassium present in them.
7. There is striking similarity between the aberrations induced by decaying organic substances like compost, cowdung and oil cakes and those reported as occurring spontaneously. It is suggested that decaying organic matter which is present in plant environment under natural conditions in varying concentrations, and those added as manures in agricultural practices, are responsible for some at least of such spontaneous mutations which play an important part in the evolution of species.