Pest management after transplantation is essential in horticultural production, because early infections can spread throughout the crop. Therefore, in transplant production, the transplants are sprayed with pesticides before shipping.
Recently, closed-type transplant production systems (CTPS) that use artificial light have been developed as a way to produce high-quality transplants regardless of the weather (Kozai, 2007; Kozai et al., 2006). The use of pesticides can be omitted, because the systems are closed to pathogens and their vectors. In addition, the growing of transplants in CTPS could further reduce the use of pesticides after transplantation through the improvement of plant resistance to pathogens by illumination with artificial light; plant resistance to diseases can be improved by illumination at particular wavelengths, notably ultraviolet (Brederode et al., 1991; Bridge and Klarman, 1973), violet (Wang et al., 2010), blue (Wang et al., 2010), or red (Islam et al., 2002; Khanam et al., 2005; Rahman et al., 2002; Schuerger and Brown, 1997; Wang et al., 2010).
Here, we focused on the R:FR of typical commercial fluorescent lamps commonly used in CTPS. Cucumber seedlings grown under fluorescent lamps with a high R:FR have thicker leaves and consequently higher photosynthetic ability (Shibuya et al., 2010a) and lower attractiveness to sweetpotato whitefly (Shibuya et al., 2010b). The morphological and physiological changes are probably the result of responses that are the inverse of those typical of shade avoidance (Franklin, 2008; Smith and Whitelam, 1997). Typical commercial fluorescent lamps emit little FR irradiation and consequently have higher-than-natural R:FRs. Because morphological changes in leaves might affect plant resistance to pathogens (Szwacka et al., 2009), it might be possible to improve plant resistance by high R:FR illumination. To test this hypothesis, we investigated the effects of adaptation to illumination with high R:FR fluorescent light on the resistance of cucumber (Cucumis sativus) seedlings to PM (Sphaerotheca cucurbitae) in an inoculation test.
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