The efficiency of γ-irradiation as a tool for breeding grapevine rootstocks was investigated. One-bud cuttings from vitroplants of two varieties (Fercal and Gravesac) were subjected to gamma rays from Cs137 source at rates from 10 to 60 Grays (Gy) at intervals of 10. All the parameters observed were affected at 20 Gy and upwards. Varietal susceptibility to irradiation was different since the maximum withstanding dose was 40 Gy for Gravesac and only 30 for Fercal. Besides, shoot development was more lowered than root development. The results showed that an increase of the irradiation dose decreased the rate of survival, the rhizogenesis and the growth of in vitro plants. On the V2 vegetative generation ofGravesac vitroplants changes in size, in leafform, in plant habits, in growth and chlorophyll deficient mutations were recorded. Moreover, after a 30 Gy irradiation variations of growth, dry weight, leaf area, number of stomata and photosynthesis rates were shown on the V3 generation. Accordingly this irradiation method is efficient to develop an in vitro variability. A sample of the surviving plants was established in the greenhouse for further screening.
(1) Communication faite au 6'®me Symposium International sur l'Amélioration de la Vigne, à Yalta (Crimée), Ukraine, du 4 au 10 septembre 1994
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