Screening and phenotypic characterization of EMS-induced mutants with elite agronomic traits in broomcorn millet

Ethyl methanesulfonate (EMS) mutagenesis is an effective approach for creating genetic diversity in broomcorn millet (<italic>Panicum miliaceum</italic> L.) and for developing novel mutant lines with improved agronomic traits. Using the landrace ‘Heishuzi’ as the starting material, we conducted a two-factor completely crossed experimental design with six EMS concentrations (0, 0.4%, 0.6%, 0.8%, 1.0%, and 1.2%) and five soaking durations (6, 8, 10, 12, and 14 h), yielding 30 treatment combinations. EMS significantly inhibited seed germination, and germination rate decreased progressively with increasing EMS concentration and longer soaking duration. Based on phenotypic variation, 18 distinct mutant phenotypes were identified, including dwarf, compact panicle, leaf-color variants, early maturity, and single tillering. In the M₂ population, 297 mutant plants were recovered (mutation frequency, 28.89%); dwarf mutants were the most common (35 plants), whereas single-tillering mutants were the least frequent (5 plants). In the M₃ population, 215 mutant plants were obtained (mutation frequency, 20.91%), with early-maturing mutants being the most abundant (35 plants) and single-tillering mutants remaining relatively rare (6 plants). In addition, 215 M₃ lines were genotyped with 85 broomcorn millet-specific SSR markers; 12 markers with clear amplification and high polymorphism were selected, and 44 mutant plants were identified (variation frequency, 4.3%). Electrophoretic banding patterns indicated 32 mutants with additional bands, 6 with missing bands, and 6 with locus variation. Agronomic evaluation of these mutants identified 1 compact-panicle plant, 21 dwarf plants (60-70 cm in height), 11 early-maturing (55-60 days) plants, and 2 single-tillering plants. Collectively, these results provide valuable germplasm resources for genetic improvement and breeding in broomcorn millet.