Enhancing genetic diversity in Coffea arabica L. through induced mutagenesis

Induced mutagenesis is a powerful tool for enhancing genetic diversity and introducing novel agronomic traits, particularly in annual seed crops. However, its application in horticultural crops like Coffea arabica remains limited. Genetic improvement in C. arabica is hindered by its narrow genetic base, long reproductive cycle and the rapid decline of wild relatives. This study evaluated the effects of ethyl methanesulfonate (EMS) and gamma irradiation on seed germination, seedling growth, flowering and fertility in C. arabica. Seedling assays revealed that low EMS concentrations (0.2–2 %) stimulated germination, while higher concentrations (4–6 %) and increasing gamma radiation doses (20–100 Gy) progressively reduced germination rates. Long-term monitoring of mature M1 plants showed that gamma irradiation induced stable mutant phenotypes such as dwarfism, altered leaf morphology and chlorophyll defects that persisted from seedling to reproductive stage. In contrast, EMS-treated M1 plants appeared phenotypically similar to wild-type controls. Both mutagens influenced flowering and seed set. Gamma irradiation (50 Gy) induced early flowering and increased sterility, while EMS caused delayed flowering with reduced sterility. Notably, the altered leaf phenotypes and chlorophyll defects were also observed in the M2 progeny, providing initial evidence of stable transmission of induced mutant traits. These findings highlight the importance of applying a range of mutagen doses to mitigate mutagen-induced infertility. They also show, for the first time, that gamma- and EMS-induced genetic variation in C. arabica can be stably transmitted, offering a promising strategy to broaden its narrow genetic base.