Determination of Gamma Rays Lethal (LD₅₀) and Growth Reduction (GR₅₀) Dose in <scp><i>Chenopodium quinoa</i></scp> Varieties (UAF‐Q7 and UAF‐QS) for Mutation Breeding

ABSTRACT This investigation was initiated to determine the lethal dose (LD 50 ) and growth reduction dose (GR 50 ) for quinoa. In three series of experiments, seeds of two quinoa varieties (UAF‐Q7 and UAF‐QS) irradiated with gamma rays (Cs‐137 source) dosage 0, 50, 100, 150, 200, 250, 300, 600, 900, 1200, 1500, 1800, 2000, 2200 and 240 Gy were sown in Petri plates, soil‐filled plastic boxes and sand‐filled plastic pots. In Experiment‐1, germination process delayed, and morphological attributes decreased significantly with the increase of radiation dose. However, final germination percentage was not affected. Simultaneously, seeds treated with 600 to 2400 Gy were also sown in soil‐filled plastic boxes. All the germination and growth attributes were significantly affected, but maximum decrease in growth attributes and delay in emergence percentage was noted at 2400 Gy. LD 50 determined on the basis of germination performance was ~1800 Gy for Q7 and ~2000 Gy for QS. But M 1 seeds were not obtained after sowing in the field at those doses as seedlings died after 15–18 days with no appearance of true leaves. In Experiment‐III, seeds treated with 0 to 2400 Gy were grown in sand‐filled plastic pots, and data were collected after 40 days. Surprisingly, no seedling survived above 250 Gy in both varieties. At this dose, morphological attributes, vigour index (VI) and true leaf appearance time significantly varied under gamma rays' treatments. Furthermore, the same dose also delayed the appearance of first, second, third and fourth pair of true leaves in both varieties. On the basis of the data, the recommended GR 50 for mutation breeding for quinoa was 200 and 150 Gy for Q7 and QS varieties, respectively, as M 1 seeds were obtained at these doses.