Radiosensitivity of Hebe ‘Oratia Beauty’ and ‘Wiri Mist’ irradiated in vitro with γ-rays from 60Co

Hebe ‘Oratia Beauty’ and ‘Wiri Mist’ were micropropagated and nodal explants were used to determine their radiosensitivity, in vitro. A source of γ-rays was used to deliver doses of 20, 30, 40, 50 Gy for ‘Oratia Beauty’ and 15, 30, 45, 60 Gy for ‘Wiri Mist’. After irradiation, the fresh weight gain/loss of the single nodal explants was measured over two consecutive culture periods and the dose resulting in a 50% loss in fresh weight was computed as the LD50 value. With ‘Oratia Beauty’, the LD50 was determined as 37 Gy from the first culture period and 33 Gy from the second. The cultivar ‘Wiri Mist’ was the least sensitive to radiation: its LD50 was determined at a dose of 48 Gy from the first culture period and 56 Gy in the second. The recovery of putative mutants was higher in the more radiosensitive cultivar, ‘Oratia Beauty’ (7.1%), than in ‘Wiri Mist’ (2.2%).

► Hebe cultivars expressed differential sensitivity to ionising radiation.
► In vitro culture of nodal explants is a useful system to determine LD50 values.
► LD50 values for Hebe ranged from 33 to 56 Gy.
► Putative mutants were obtained in Hebe (2.2% and 7.1%, according to the cultivar).