Induction of flowering with a photoperiod extension coupled with gibberellic acid treatment: physiological and molecular insights in Allium species

Abstract Allium species are valued for their culinary and medicinal applications, with flowering and bulbing being key developmental processes regulated by photoperiod and temperature. In short-day, many Allium species exhibit limited floral induction, hindering their potential in breeding programs. The present study aimed to (i) develop a methodology to induce flowering under non-inductive conditions and (ii) elucidate the molecular mechanisms regulating florogenesis and bulbing in A. cepa, A. sativum, and A. tuberosum. A photoperiod extension system (10 h daylight followed by 8 h artificial light) coupled with gibberellic acid (GA3; 50, 100, 200 mg/L) treatment was standardized and applied to wild Allium species (A. tuberosum, A. fasciculatum, A. macranthum A. schoenoprasum). Results revealed that 200 mg/L GA3 combined with an 18-hrs photoperiod significantly promoted early scape emergence and flowering in A. tuberosum. In contrast, scape induction was not observed in other species under any treatment combinations. In our parallel experiment, expression profiling through qRT-PCR indicated that FT1, FT3, and FT4 genes were associated with bulbing, while FT2, CO, and LFY were key regulators of flowering. High expression of LFY, AP1, SEP3, and PI in A. cepa and A. tuberosum was correlated with successful floral transition, whereas their suppression in A. sativum underpinned its non-flowering phenotype. Additionally, the flowering repressor FLC was up-regulated during bulbing but down-regulated during flowering, reinforcing its antagonistic role in florogenesis. This work provides new insights into the florogenesis and bulbing regulatory network under short-day conditions and underscores the pivotal role of LFY in promoting flowering in Allium species. The findings offer a framework for future genetic manipulation strategies, including LFY overexpression to induce flowering in sterile garlic cultivars and LFY knockdown to control bolting in bulb onions.