Lighting from red and blue light-emitting diodes (LEDs) is common for crop production in controlled environments. Continuous application of red or blue light at night has been shown to suppress sporulation by Peronospora belbahrii, the causal organism of basil downy mildew (DM), but the suppressing effects of intermittent applications of red and blue LEDs have not been thoroughly researched. This study examined the effects of red (λmax = 670 nm) and blue (λmax = 458 nm) LED top lighting, at two photosynthetic photon flux densities (PPFD = ≈12 and ≈60 µmol·m−2·s−1), using continuous (10-hour) nighttime and two intermittent nighttime exposures, to suppress basil DM sporulation. The two intermittent treatments consisted of one 4-hour exposure and three 1.3-hour exposures spaced 3 hours apart. Continuous nighttime treatments with blue or red LED top lighting at ≈60 µmol·m−2·s−1 were able to suppress basil DM sporulation by more than 99%. At a given nighttime dose of light that did not completely suppress sporulation, continuous lighting was more effective than intermittent lighting, and for these partially suppressing doses, red LEDs were not significantly different from blue LEDs for suppressing sporulation. The present study showed that horticultural lighting systems using red and blue LEDs to grow crops during the day can also be used at night to suppress basil DM sporulation by up to 100%.
Leora Radetsky, Jaimin S. Patel, and Mark S. Rea
Jaimin S. Patel, Shouan Zhang, and Maria I. Costa de Novaes
Sweet basil (Ocimum basilicum) is an important annual culinary herb grown in the United States. Recently, basil production was drastically affected by downy mildew caused by Peronospora belbahrii, a recently discovered foliar disease of basil in Homestead, FL. The disease has spread to more than 30 states in the United States causing significant losses to basil growers. As a result of the recent emergence of the disease, limited management tools are available for control of downy mildew, and it is critical for growers to apply management measures at appropriate times. This study was designed to evaluate 2- to 7-week-old basil plants for their susceptibility to downy mildew. Another objective of the study was to evaluate the effect of a pre-inoculation application of acibenzolar-S-methyl (ASM) for control of downy mildew. The results suggested that 2- to 3-week-old basil was more susceptible to downy mildew than 4- to 7-week-old plants. The area under the disease progress curve (AUDPC) was smaller for 5- to 7-week-old ASM-treated basil plants than for 2- to 4-week-old ASM-treated basil plants. This study indicated that 2- to 3-week-old basil plants need to be protected, and ASM should be applied before pathogen infection on 5- to 7-week-old plants to reduce downy mildew to a greater extent.