Radiosensitivity of seeds and nodal segments of citrus rootstocks irradiated in vitro with gamma-rays from 137Cs

The first step in a breeding program involving physical mutagenesis by radiation is to evaluate the sensitivity in the plant material. Seeds of Citrus aurantium and C. macrophylla and nodal segments, where the buds were completely removed, from micropropagated explants of macrophylla, were used to determine their radiosensitivity to gamma radiation. A 137Cs source of gamma-rays was used to deliver doses of 0, 10, 20, 30, 40 and 50 Gy for nodal segments, or between 0 and 250 Gy for seeds. After irradiation, the loss of germination percentage or organogenesis efficiency was measured over two consecutive culture periods and the dose resulting in a 50% loss in germination or regeneration frequency was computed as the LD 50 value. For nodal segments of C. macrophylla, the LD 50 was determined as 29.2 Gy. Seeds of sour orange were the least sensitive to radiation, its LD 50 was determined at a dose of 155.6 Gy while the LD 50 in seeds of macrophylla was of 129 Gy.