γ-線 緩照射에 의한 柑橘의 芽條變異 誘起選拔

Studies on the Induction and Selection of Bud Sport by Chronic Gamma Irradiation on Citrus Tree

In order to induce mutation, especially bud sports of cold hardiness, several varieties of Citrus Unshu were chronically irradiated to the γ-rays (⁶⁰Co) differing in dose rate and total dose during different growing stages. Scions and buds from the irradiated plants during dormant and growing stage were grafted on the stock of trifoliate orange and survival rate and growth of grafts were examined. Growth inhibition, deformation and mutation in the irradiated plants during the growing stage were observed. In April, cutting back method was applied to the irradiated plants during dormant stage. The results obtained were as follows: 1. Survival rates of scion grafts from the irradiated plants during dormant stage showed no differences compared with the control at the dose applied (7.69 kR, 15.1R/hr.) in four varieties. 2. In four varieties, survival rates of bud grafts from the irradiated plants during growing period were more than 50% (RD-50) as compared with the control even at the highest dose applied (34.7kR, 18.06 R/hr.). 3. In chronic irradiation during growing period internodial length, petiole length, leaf length, leaf width and leaf area were significantly decreased with increasing dosage. 4. Deformation following irradiation were mostly appeared at higher doses. Deformed leaves were characterized by asymmetry, bifurcation, irregular toothed margin, slender shape, thickness and dark greenness. Also, deformed fruits showed basal protuberance, rugous and thick rind and lower sugar content. Adventitious shoot with untoothed, round, large, thick and dark green leaves also developed from the base of stalk. 5. In three varietieties four individuals with small leaved and compact type were preliminarily selected as cold hardy character from cutting back treated plants.