The Flowering Duration Blind Spot in Grain Legumes.

Increasing legume yield stability is vital for diversification and sustainability of farming systems. Flowering duration, the period from the onset to the end of flowering, remains one of the most overlooked traits in grain legume research despite its potential importance for adaptation and productivity. Flowering duration may be particularly consequential in grain legumes, where indeterminate growth habits are common, leading to extended reproductive periods. Extended flowering duration lengthens the window over which reproduction is exposed to stress, and may also enable recovery through continued flower production, although neither the benefit nor its cost has been quantified in grain legumes. Narrow flowering duration simplifies agronomic management, particularly harvest. The optimal flowering strategy is therefore likely to be context dependent, yet without systematic measurement we cannot determine which duration patterns suit which production systems. This neglect reflects a measurement problem rather than a lack of importance, since characterising flowering duration requires repeated observations throughout the reproductive period that are prohibitively labour-intensive. High-throughput phenotyping tools now make this feasible, enabling characterisation. Here we synthesise what is known of the mechanisms controlling flowering duration, identify where evidence is lacking, and argue that flowering duration warrants systematic investment to quantify its value and harness natural variation for breeding climate-adapted legume varieties.