EFFECT OF RADIATION ON CHIASMA FREQUENCY IN SUNFLOWER (HELIANTHUS-ANNUUS)

Chiasma frequencies were determined following seed irradiation of three varieties of H. annuus. Histograms of chiasma frequencies between nuclei, show differences between the controls of the three varieties studied. Differing varietal response to radiation was indicated at high doses with a marked reduction in chiasma frequency with dose in one variety and a tendency in this direction in the two others, as shown by the slopes of the regression lines for Xta on dose. Reduction in the mean chiasma frequency is found to be associated with decline in the mean squares within nuclei. There is a lack of correlation between different bivalents of the nucleus both in the control and irradiated material and this, as in other plants, is found to be associated with the symmetrical nature of the karyotype in this plant. © 1979, Japan Mendel Society, International Society of Cytology. All rights reserved.