Optimizing Daily Light Integral in Seedling Stage Accelerates Heading and Flowering in Wheat Under LED Lighting

Overview

This study investigated optimal daily light integral (DLI) conditions during the seedling stage for accelerated wheat development in controlled plant factory environments using light-emitting diode (LED) illumination. The research addressed a gap in lighting strategy recommendations for speed-breeding systems by systematically evaluating the interaction between light intensity and photoperiod duration on seedling quality and subsequent developmental timing.

Methods and approach

The experimental design incorporated three photosynthetic photon flux densities (300, 500, and 700 μmol m−2 s−1) combined with four photoperiod durations (10, 14, 18, and 22 h d−1), generating nine distinct DLI conditions ranging from 10.8 to 55.4 mol m−2 d−1. Seedling quality was assessed through seedling index calculations and root-to-shoot ratio measurements. Photosystem performance was quantified using chlorophyll fluorescence analysis. Seedlings were subsequently transplanted and monitored for developmental progression to heading and flowering stages, with timing comparisons made across treatment groups.

Results

An optimal DLI of 39.6 mol m−2 d−1 (achieved using 500 μmol m−2 s−1 intensity with a 22 h d−1 photoperiod) yielded the highest seedling index (0.26) and root-to-shoot ratio (0.42), alongside enhanced photosystem performance. Seedlings grown under this optimal DLI reached heading 5.9 days earlier and flowering 7.5 days earlier compared to the lowest DLI treatment (10.8 mol m−2 d−1). Increasing DLI beyond 39.6 mol m−2 d−1 resulted in plateauing of seedling quality parameters and shoot biomass accumulation, indicating diminishing returns from further light intensity or duration increases.

Implications

The identified optimal DLI of 39.6 mol m−2 d−1 provides a quantitative lighting framework for maximizing seedling quality in controlled environment agriculture systems dedicated to wheat speed-breeding. This specification enables accelerated developmental progression while maintaining physiological vigor, thereby reducing the time required to advance breeding cycles under artificial lighting. The plateau effect above optimal DLI suggests that excessive radiation represents an inefficient allocation of energy resources in controlled environment production systems and establishes a practical threshold for lighting system design in plant factory operations.