Abstract
Leaves of lettuce, pepper, tomato and grapevine plants grown in greenhouse conditions were exposed to UV-C light for either 60 s or 1 s, using a specific LEDs-based device, and wavelengths and energy were the same among different light treatments. Doses of UV-C light that both effectively stimulated plant defences and were innocuous were determined beforehand. Tomato plants and lettuce plants were inoculated with Botrytis cinerea, pepper plants with Phytophthora capsici, and grapevine with Plasmopara viticola. In some experiments we investigated the effect of a repetition of treatments over periods of several days. All plants were inoculated 48 h after exposure to the last UV-C treatment. Lesions on surfaces were measured up to 12 days after inoculation, depending on the experiment and the pathogen. The results confirmed that UV-C light stimulates plant resistance; they show that irradiation for one second is more effective than irradiation for 60 s, and that repetition of treatments is more effective than single light treatments. Moreover a systemic effect was observed in unexposed leaves that were close to exposed leaves. The mechanisms of perception and of the signalling and metabolic pathways triggered by flashes of UV-C light vs. 60 s irradiation exposures are briefly discussed, as well as the prospects for field use of UV-C flashes in viticulture and horticulture.
Highlights
IntroductionThere is the need to develop alternative or complementary solutions to pesticides (to decrease their use) that are effective, safe and economically viable
There is the need to develop alternative or complementary solutions to pesticides that are effective, safe and economically viable
Lesions areas increased over time in all control and treated plants, but single 60 s irradiations by UV-C light reduced them by 35% in tomatoes two days after inoculation with Botrytis cinerea, by 17% in lettuce three days after inoculation with Botrytis cinerea, and by 35% and 21% in peppers, three and four days, respectively, after inoculation with Phytophthora capsici (Fig 4)
Summary
There is the need to develop alternative or complementary solutions to pesticides (to decrease their use) that are effective, safe and economically viable. Chemical elicitors of plant defences are on the rise but their development is limited by inconsistent efficacy as a consequence of problems of formulation and stability in field conditions [1]. Physical elicitors do not present these drawbacks and have the additional advantage that they can be combined with other existing methods of treatment, either chemical or biological [2]. UV-B radiation has been observed to increase plant resistance to pathogens [3, 4]. UV-B light is known to act through signalling pathways, involving notably mitogen-activated protein kinases, which closely resemble those for pathogens [5]. It has been observed that UV-C light can stimulate plant and crop defences against Botrytis cinerea and Sclerotinia minor [6,7,8,9,10,11].
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