Flowering Management in Sugarcane Breeding: The Role of Photoperiodic Treatments

Abstract

Flowering is indispensable for sugarcane improvement because commercial varieties are developed through sexual recombination, yet sugarcane is normally vegetatively propagated and many elite clones flower erratically, late, poorly, or not at all under local conditions. Sugarcane flowering is controlled mainly by photoperiod, but successful panicle emergence and pollen fertility also depend on plant age, genotype, temperature, humidity, soil moisture, nutrition, light intensity and post-initiation development. The reviewed literature shows that sugarcane behaves as an intermediate/quantitative short-day plant whose inductive window is commonly close to 12.0-12.5 h or a declining schedule beginning near 12 h 45 min to 12 h 55 min; deviations to 9, 11 or 14 h markedly reduce panicle emergence compared with 12.5 h in sensitive clones. Controlled facilities therefore use either a fixed inductive photoperiod for 30-60 cycles followed by daily shortening, or a programmed daily decline of 30, 45 or 60 s from 12 h 55 min until about 11 h 30 min. Breeding programmes use these treatments to induce shy-flowering parents, advance early parents, delay early parents by night-light interruption, and synchronise late Saccharum spontaneum or wild relatives with commercial hybrids. Optimal controlled conditions are not universal, but the most consistently useful range is approximately 21-32 degrees C for development, 18-31 degrees C as a favourable seasonal flowering range, night temperature above about 18 degrees C, relative humidity about 67-80 per cent or higher during pollen functioning, continuous water availability without waterlogging, and avoidance of both nutrient starvation severe enough to weaken plants and excessive nitrogen during floral initiation. Molecular evidence indicates that circadian, photoperiod, gibberellin and age-related pathways interact through FT-like genes, CO-like regulators, LFY/AP1/SOC1-like floral integrators and GA-related regulators such as ScGAI and ScNAC23. This review synthesises photoperiodic schedules, environmental targets, nutrient management, breeding applications and gene-level information into a practical framework for controlled sugarcane flowering.