Physiological and morphological responses of strawberry seedlings to end-of-day far-red light

The agronomic quality of cutting-propagated strawberry seedlings is a critical determinant of subsequent field performance and economic returns in the annual production of fresh-market strawberries. Although far-red light (FR) has been well established as a key regulator of plant architecture and productivity in many horticultural crops, its specific physiological roles during the strawberry seedling establishment stage remain poorly understood. Thus, investigating whether end-of-day far red (EOD-FR) light treatment can effectively enhance the growth vigor and overall development of strawberry runners addresses a significant knowledge gap, with direct implications for commercial seedling production systems.

The experiment investigated the effects of 0 (CK), 3 h, 6 h, and 9 h EOD-FR durations on strawberry cuttings (Fragaria × ananassa Duch. cv. Benihoppe). The 60-d period experiment was conducted in a solar greenhouse, employing a completely randomized block design. The sampling was carried at 30 d and 60 d to assess physiological and morphological responses of strawberry seedlings.

Compared with the control (CK), 6 h EOD-FR supplementation markedly enhanced seedling growth, including increases in height, leaf area, petiole diameter and length, biomass accumulation, root development and vigor index. In addition, anatomical observations revealed that while prolonged EOD-FR exposure led to reduction in leaf thickness, the 6 h EOD-FR increased the number of vascular bundles in petioles and accelerated floral bud differentiation. The physiological analysis showed that 6 h EOD-FR supplementation enhanced net photosynthetic rate and stomatal conductance, and water use efficiency. This was observed alongside increased activities of antioxidant enzyme and greater accumulation of osmolytes, including free amino acids, soluble sugars, and proteins. Hormonal profiling indicated that 6 h EOD-FR increased the IAA, Brassinosteroids, and ABA levels in leaves and petioles. However, the marked increase of ABA content and reduce of GA₃ content were only found in shoot apices. Based on membership function values and principal component analysis, the order of treatment performance (6 h > 3 h > CK > 9 h) was consistent across both 30-d and 60-d experimental durations.

In summary, supplementation with 6 h EOD-FR optimizes photosynthetic performance, strengthens antioxidant capacity, regulates hormone balance, and promotes nutrient accumulation in strawberry seedlings, ultimately leading to enhanced growth and stimulated floral induction.