Impact of a High-PAR Transmittance and High Light Diffusivity Plastic Cover on Photosynthetic Activity and Development of Cucumber (Cucumis sativus L.) Crops in a Mediterranean Greenhouse

Light quality within greenhouses is a critical factor for crop development and is essential for optimal photosynthetic activity. Modifying the optical properties of cover materials can significantly enhance crop performance. This study aimed to assess the effects of an experimental plastic cover, characterized by high transmittance of photosynthetically active radiation (PAR) and high light diffusivity, on the growth, yield, fruit quality, photosynthetic activity, and fungal disease incidence in two cucumber (Cucumis sativus L.) crops. The trials were conducted over two consecutive autumn-winter crop seasons in a multispan greenhouse divided into two sectors, separated by a vertical polyethylene sheet. The experimental plastic cover was installed in the West sector (40 m × 25 m), while a standard commercial cover was used in the East sector (40 m × 20 m). Results demonstrated that plants grown under the experimental cover exhibited an 8.5% and 15.3% increase in photosynthetic activity during the first and second crop seasons, respectively. PAR radiation at the canopy level was also higher in the experimental sector by 8% and 10.5% across both seasons. Additionally, marketable yield increased by 4.2% in the first season and 14.3% in the second season under the experimental cover. No significant differences were observed in fruit quality and plant growth parameters between the two sectors. The experimental plastic cover, with its high PAR transmittance and light diffusivity, enhanced the internal light environment of the greenhouse without incurring additional costs. This improved light environment positively influenced photosynthetic activity and yield in cucumber crops. Furthermore, a lower incidence of fungal diseases was observed in plants grown under the experimental cover during both crop cycles.