EFFECT OF GAMMA AND ULTRAVIOLET-IRRADIATION ON ADVENTITIOUS REGENERATION FROM INVITRO CULTURED PEAR LEAVES

Irradiation of in vitro explants and subsequent adventitious regeneration has been tested for 4 commercially important varieties of pear (Pyrus communis) with the aim to create mutants with a reduced susceptibility to fire-blight (Erwinia amylovora). The effect of gamma and ultraviolet irradiation of leaves on adventitious regeneration ability has been studied. The LD50 (50% decrease of regeneration) after gamma irradiation was genotype-dependent and was between 20 and 50 grays. The curves of regeneration showed a threshold dose underneath which none or a very slight decrease was registered. The decrease might result from cumulative events. After an ultraviolet irradiation as low as 62.5 J/m2 , the leaves became crumbly and rolled up, and their metabolism seemed to be altered. The LD50 was about 125 J/m2 for all varieties and the decrease of regeneration was linear. Histological investigations showed leaves with flattened epidermal cells after ultraviolet irradiation and slack spongy parenchyma after gamma irradiation.