Speed breeding for pearl millet and wild Pennisetum species with optimized pot size, CO₂ supplementation, and ABA application

Pearl millet (Pennisetum glaucum, syn. Cenchrus americanus, 2n = 2x = 14) is a crucial cereal food and fodder crop in the semi-arid tropic dryland, yet breeding progress is slow and threatened by climate change. Speed-breeding methods that shorten generation time are established for several crops, but none exist for pearl millet or its wild relatives. We evaluated three factors pot volume, supplementary CO₂, and exogenous abscisic acid (ABA) to develop a rapid-cycling protocol for cultivated P. glaucum and three wild Pennisetum species (P. mollissimum, P. violaceum, and P. schweinfurthii). Flowering occurred within 64 days from sowing in 220 cm³ pots for P. glaucum and P. mollissimum and in 38 cm³ pots for P. violaceum and P. schweinfurthii, enabling up to four generations per year. Supplemental CO₂ increased vegetative biomass and shortened time to flowering by 14 days only for P. schweinfurthii. ABA application curtailed plant height without affecting phenology, facilitating high-density cultivation. Combining small pots with ABA permits rapid, space-efficient generation cycling across multiple Pennisetum taxa. The protocol closes a key gap in millet improvement pipelines and will accelerate introgression of stress-resilience alleles from wild relatives into elite germplasm.