When the numbers of live/damaged cell signals in FCM dot plots were approximately 10% of the total number of cells, a regrowth check was performed for verification. For exp-I this procedure was carried out at day 22 for samples treated with 100–200 mJ/cm2 and at day 2 for samples treated with 400 and 800 mJ/cm2, and for exp-II at day 20 for samples treated with 100–200 mJ/cm2and at day 3 for samples treated with 400 and 800 mJ/cm2. 1 ml of the sample was added to 9 ml growth medium in 50 ml Erlenmeyer flasks. No visible change to green color indicated that there were no reproductive cells in the sample. The flasks, trays and plates were incubated at 15 ฐC in the dark for 3 weeks.