Intensity of Supplemental Greenhouse Lighting Affects Strawberry Plant Growth, Anthracnose Infection Response, and Colletotrichum Pathogen Development in Culture

The effect of supplemental lighting on strawberry growth and anthracnose disease response of three strawberry ( Fragaria × ananassa ) cultivars was evaluated in two greenhouse trials, and the effect on strawberry anthracnose pathogens ( Colletotrichum sp.) was evaluated in the laboratory. The objective of the greenhouse trials was to determine the effect of various intensities of the red and blue light emitting diode (LED) light treatment on strawberry plant vigor, injury, and disease development. In these trials, the duration of supplemental light treatments was split into two 4-hour periods: dawn and dusk. The intensity of the red and blue LED bulbs was set using an adjustable dial at 1 or 3 in trial 1 and at 1, 5, or 10 in trial 2. Illuminance and photosynthetic photon flux densities of the light treatments ranged from lows of 402 lx and 5 μmol⋅m –2 ⋅s –1 (blue LED 1) to highs of 575 lx and 25 μmol⋅m –2 ⋅s –1 (red LED 1 + blue LED 3) in trial 1, and from lows of 4213 lx and 81 μmol⋅m –2 ⋅s –1 (red LED 1) to highs of 7051 lx (red LED 5) and 194 μmol⋅m –2 ⋅s –1 (red LED 10) in trial 2. Lower light intensities in trial 1 resulted in no significant differences as a result of light treatments in relative chlorophyll content, plant vigor ratings, or disease severity ratings (DSRs). However, plant injury ratings were significantly greater in plants in the wide-spectrum fluorescent (WSF) plus ultraviolet B (UVB) light treatment compared with 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 LED 1 treatments was significantly greater than that of plants in the red LED 10 treatment; however, plants in the red LED 10 treatment had the greatest injury ratings. Detached leaves from plants in the red 5 LED and red 10 LED treatments inoculated with Colletotrichum gloeosporioides received the greatest DSRs, and leaves from plants in the red LED 1 and WSF treatments received the lowest DSRs. In the laboratory, five days of 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 was set at their highest intensity. However, growth of isolates exposed to the WSF + UVB light treatment was slowed.