Soilless-Grown Green and Purple Basil Response to High Tunnel Photo-Selective Covering Films

Protected cultivation systems, such as high tunnels, have gained popularity for their ability to enhance growth conditions and extend the growing season of horticultural crops. The choice of the covering film in these systems can significantly impact crop productivity and quality while influencing pest and pathogen incidence. This study aimed to evaluate the yield, physiological responses, and nutritional quality of green and purple basil grown in high tunnels using different plastic film covers. The study was conducted in Central Pennsylvania using twelve research high tunnels covered with four alternative polyethylene films with varying light diffusion and ultraviolet (UV) radiation transparency levels: TuffLite IV (TIV), KoolLite Plus (KLP), UV-transparent (UVT), and UV-opaque (UVO). Green ‘Genovese Compact Improved’ and purple ‘Amethyst Improved’ basil (<i>Ocimum basilicum</i> L.) cultivars were grown as test crops. The plastic covering film had a significant effect on the growth of both basil cultivars, with a significant interaction between the film and basil genotype. Green basil generally exhibited higher fresh and dry biomass compared to purple basil, and the film effect varied with the basil genotype. Leaf area, stem, leaf, and total plant biomass were influenced by the plastic cover, with UVO and UVT films resulting in higher biomass production. The plastic covering films showed varying effects on the mineral content, total chlorophyll, carotenoids, total phenolic compounds, and antioxidant activity, with UVO and UVT films often resulting in improved nutritional quality compared to traditional films. Furthermore, covering films influenced the downy mildew severity on both cultivars and the UVT film consistently limited the severity of the foliar disease in both genotypes. Overall, this study highlights the importance of selecting appropriate plastic covering films with varying levels of UV transparency in high tunnel production systems.