Enhancing greenhouse plant production and pathogen resistance through monochromatic LED light supplementation and ozonated water: a priming effect study

The production of food with increased nutritional properties and the reduction of agrochemical inputs are hot topics in agriculture. A possible way to achieve these goals is offered by a process called “priming” in which a controlled imposition of stressor factors activates plant defence mechanisms which enable plants to deal with subsequent stressor outbreaks or pathogen infection. The present work focused on the application of two different abiotic elicitors, namely LED monochromatic light supplementation and ozonated water application, to prime plants with the twofold purpose of increasing nutraceutical properties and enhancing plant defence mechanisms against pathogens. A highly valuable fruit species, strawberry (Fragaria × ananassa Duch.), and a leafy green species, basil (Ocimum basilicum L.) were used as models to test the possible application of the two elicitors as primers. Pre-treatment application of 250 μmol m-2 s-1 of monochromatic red, blue, green, or polychromatic white LED light was used as supplemental light on both species. The most interesting results in strawberry plants were obtained after red light supplementation. In fruits, red light induced the highest yield and anthocyanin accumulation, as well as an increased pathogen tolerance against post-harvest infection of Botrytis cinerea through the upregulation of genes involved in cell wall defences, inhibition of fungus polygalacturonases, and the degradation of B. cinerea beta-glucans. Moreover, in leaves, red light promoted the activity of antioxidant enzymes, thus potentially explaining the boosted fruit tolerance to the pathogen. Instead, in green and red-leafed basil, all the lights induced alteration in metabolome and volatilome leaf profile, suggesting the possibility of modifying the leaf flavour through the light spectrum, but also causing an increase in the in vitro fungistatic properties of its essential oil against B. cinerea. On the other hand, ozonated water used for irrigation did not show any property as a priming agent at the concentration used, and with the pathosystems tested, in the present thesis. In fact, we did not observe any increase in the overall fungistatic properties of essential oil of basil irrigated with ozonated water, nor differences in Fusarium oxysporum development after inoculation in plants pre-treated with ozonated water. To conclude, supplemental monochromatic LED light can be a feasible alternative to common illumination in agriculture, as the fine-tuning of the light spectrum can improve both production quality and tolerance to pathogens like B. cinerea. At the same time, more research is needed about ozonated water applications in agriculture, but results suggest its ineffectiveness as a priming agent.