An EMS mutagenesis protocol for sugar beet and isolation of non-bolting mutants

An annual sugar beet line homozygous for the dominant gene for early bolting (B) has been mutagenized with different doses of ethylmeth‐anesulfonate (EMS). Approximately 15 000 M1 seeds were treated with EMS doses between 0.5 and 1% for 4, 6, 8, 12 and 14 h. Among 10 066 M1s, plants with chlorophyll defects and other abnormalities were found. Germination rates ranged between 30 and 100%, whereas the fertility of M1s dropped to 36%. A dose of 1% EMS applied for 8 h was found to yield an acceptable rate of M2 sterility (16%). Exactly 0.5% of the M2 families contained plants with altered bolting behaviour. After selfing these M2 plants, five non‐bolting M3 lines were selected. These plants do not exhibit shoot elongation even after cultivation under long‐day conditions. Thus, they are homozygous for new mutagenized, recessive non‐bolting alleles. Moreover, four M3 lines showed delayed bolting which was clearly different from the early bolting parent. This demonstrates varying activities of the bolting gene due to different mutational events.