| Sumario: | Gamma irradiation has been widely used
as a breeding technique to obtain new cultivars
in ornamental species such as Alstroemeria,
where several cultivars have been obtained
through rhizome radiation. The optimum dosage
for an appropriate induction of mutation must be
considered for breeding purposes and it depends
mainly on plant susceptibility. Thus in this study
in vitro cultured rhizomes of Alstroemeria aurea
were irradiated with a gamma source using
different dosages to evaluate the direct effect
produced. Damage and number of rhizome
sprouting were observed and recorded during
61 days after irradiation. At the end of this period,
rhizomes were weighted and mortality was
evaluated. Both mortality and weight increased
depending on dosage. All irradiated rhizomes
showed early sprouting in comparison with
control (0 Gy) and no significant difference in final
number of shoots after 61 days among irradiated
treatments was observed. Bleaching and necrosis
was observed in all irradiated rhizomes and
was more evident at higher doses. LD50 was
established at about 40 Gy and the optimum
dosage to induce mutation was suggested
between 2.5 and 5 Gy, when the growth was
reduced in 50%, and probably this dosage could
be used for breeding purposes.
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