Comparative radiosensitivities of main and accessory buds of sweet

S. Saamin and M. M. Thompson

Abstract

For determination of LD50, dormant main buds of Napoleon exposed to 4–12 kR of acute and fractionated gamma rays were forced in the glasshouse. Forcing of unirradiated and irradiated accessory buds was also done in the glasshouse. For the field experiment, Bing main and accessory buds on dormant scions were irradiated and then grafted. Survival and growth of primary (M1V1) shoots were observed. The LD50 values were about 5.0 kR for both acute and fractionated irradiation in air, 5.5 kR for acute exposure in water and 6.0 kR for fractionated dose in water. In the Bing field experiment with main buds, the LD50 for both acute and fractionated irradiation in air was 3.5 kR. In water, the LD50 was 5 kR for acute treatment and 6.5 kR for fractionated dose. The M1V1 shoots showed 52% frequency of leaf aberrations, and 33% bifurcations and/or fasciations. In the irradiated accessory bud field experiment, bud growth was influenced by irradiation dosage, bud maturity as related to position on the scion, and vigor of scions as represented by diameter. With all treatments, the number of buds that grew per potential bud site decreased from the base towards the tip, decreased with increasing dosage, and decreased with acute as compared with fractionated irradiation. Sixteen per cent of the M1V1 shoots derived from accessory bud irradiation had aberrant leaves, two were total leaf mutants and two had shorter internodes.

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