Abstract: The shoots of pear and apple in vitro were irradiated by gamma rays． The effects of gamma irradiation on shoot regeneration from leaf and bud growth were studied． The organ which is the most sensitive to γ-rays was leaf，second was unbudding lateral bud， the third was growing shoot tip． The LD₅₀(50% decrease of regeneration)of leaf was genotype-dependent and was between 20 and 30 grays．The LD₅₀ of lateral bud also was genotype-dependent and was 30 grays or above 30 grays． Doses of iradiation were between 10 and 30 grays，the elongation growth of shoot tip was inhibited， but no lethality or other symptoms．
Key words：

Key words: Apple, Pear, Leaf, Bud, γ-rays, Tissue culture