Intensity of supplemental greenhouse lighting affects strawberry plant growth, response to anthracnose infection, and growth of Colletotrichum pathogens in culture.

Authors: Smith, Barbara; STAFNE, ERIC - Mississippi State University; Sakhanokho, Hamidou; Sampson, Blair

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2022
Publication Date: 1/4/2023
Citation: Smith, B.J., Stafne, E.T., Sakhanokho, H.F., Sampson, B.J. 2023. Intensity of supplemental greenhouse lighting affects strawberry plant growth, response to anthracnose infection, and growth of Colletotrichum pathogens in culture.. HortScience. E 58(1):127–133. https://doi.org/10.21273/HORTSCI16888-22.
DOI: https://doi.org/10.21273/HORTSCI16888-22

Interpretive Summary: Greenhouse production of strawberries in the United States is gradually increasing. It is important for growers to choose the best supplemental lighting to enhance the growth and fruiting of their crop. LED (light emitting diode) lights offer a wide range of light spectrum and intensity options. We determined that exposure to low intensity (illuminance < 7000 lux) red, blue, and red + blue LED lights caused little to no injury to strawberry plants; however, these lights did not increase plant vigor compared to the more traditional wide-spectrum fluorescent light. In one of two trials, detached leaves from plants exposed to the lowest intensity red LED light developed the least severe disease symptoms following inoculation with the strawberry anthracnose pathogen. None of the light treatments evaluated in this study halted growth of the anthracnose pathogens in agar culture in the laboratory; however, wide-spectrum fluorescent light + ultraviolet B (UV-B) light treatment did slow their growth. Results of this study are important to greenhouse strawberry growers and extension agents advising the growers on lighting options.

Technical Abstract: The effect of supplemental lighting on plant growth and response to anthracnose disease of strawberries was evaluated in two greenhouse trials, and their effect on the growth of strawberry anthracnose pathogens was evaluated in the laboratory. The objective of the greenhouse trials was to determine the effect of various intensities of the red and blue LED treatment lights on strawberry plant vigor, injury, and disease development. In both trials, the duration of supplemental light treatments was split into two 4-hour periods each centered around dawn and dusk. LEDs are capable of considerable adjustment and range in light output depending on color and intensity. The intensity of the red and blue bulbs was set with an adjustable dial at 1 (lowest) or 3 in Trial 1 and 1, 5, or 10 (highest) in Trial 2. The illuminance of the light treatments ranged from 402 lux (Blue 1 LED) to 575 lux (Red 1+Blue 3 LED) in Trial 1, and from 4213 lux (Red 1 LED) to 7051 lux (Red 5 LED) in Trial 2. Similarly, photosynthetic photon flux densities (PPFDs) ranged from 5 µmolm'²s'¹ (Blue 1 LED) to 25 µmolm'²s'¹ (Red 1+Blue 3 LED) in Trial 1 and from 81 µmolm'²s'¹ to 194 µmolm'²s'¹ in Trial 2. Lower light intensities in Trial 1 resulted in few effects due to light treatment, i.e., no significant differences in relative chlorophyll content, plant vigor ratings, or disease severity ratings (DSRs). However, plant injury ratings were significantly higher on plants in the wide spectrum fluorescent plus ultraviolet–B (WSF+UVB) light treatment compared to the other treatments. Under the higher light intensities in Trial 2, there were more significant effects among light treatments. Relative chlorophyll content of plants in the WSF+UVB, WSF, and Red 1 LED light treatments were significantly higher than that of plants in the Red 10 LED light treatment; plants in the Red 10 LED light treatment had the highest injury ratings; and detached leaves from plants in the Red 5 LED and Red 10 LED light treatments inoculated with the anthracnose pathogen, Colletotrichum gloeosporioides, received the highest DSRs while leaves from plants in the Red 1 LED and WSF light treatments received the lowest DSRs. In the laboratory, five days exposure to supplemental lights did not prevent the growth of isolates of three species of Colletotrichum pathogens even though the intensity of the LED lights in this laboratory trial were set at their highest intensity. However, growth of isolates exposed to the WSF+UVB light treatment was slowed.