Effect of LED Light Quality on Melon Seedlings Based on Growth and Photosynthetic Performances in a Closed-Type Production System

초록

Climate variability challenges conventional melon seedling production through unstable tem perature and light conditions during critical nursery stages. Closed-type systems with light- emitting diodes (LEDs) enable precise environmental control; however, optimal spectral composition must be evaluated by integrating morphological quality and physiological perfor mance. This study compared five LED spectra (Blue, Blue+Red, Red, Blue+Wide-Red+Far-Red, and White) on melon (Cucumis melo L. cv. ‘Haniwon’) seedlings grown for 28 days in a closed- type system under 300 µmol･m-2･s-1 PPFD, 16 h photoperiod, and 30/20°C day/night temperature. Growth, seedling quality indices, vegetation indices, and chlorophyll fluorescence parameters were evaluated. Red light induced excessive stem elongation, reduced compactness, and increased shoot-to-root ratios. This was accompanied by inefficient energy utilization characterized by elevated dissipation per reaction center, indicating unsuitability for commercial seedling production. In contrast, Blue and Blue+Red treatments improved structural quality by suppressing elongation and increasing stem diameter while maintaining balanced biomass allocation. White LED produced comparable morphological quality to blue-enriched spectra but demonstrated superior photosystem II functionality, as shown by the highest PRI and performance index on absorption basis (Pi_Abs). Principal component analysis separated seedling quality into two distinct dimensions: PC1 (67.7%) representing growth-related traits and PC2 (18.1%) representing photosynthetic capacity. Although White and blue-enriched treatments showed similar PC1 scores, White LED achieved markedly higher PC2 values, indicating enhanced physiological performance independent of morphological characteristics. These results indicate that optimal LED selection for closed-type melon seedling production should integrate morphological regulation with photosynthetic efficiency, with White LED offering the most balanced combination to support robust transplant establishment under variable climate conditions.

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