T Shibuya, K Itagaki, M Tojo, R Endo… – HORTSCIENCE, 2011
We investigated the effects of fluorescent illumination with a high red-to-far-red ratio (R:FR) on the resistance of cucumber (Cucumis sativus) seedlings to powderymildew fungus (Sphaerotheca cucurbitae; PM). Seedlings were grown at a photosynthetic photon flux (PPF) of300mmol_m–2_s–1 provided by fluorescent lampswith highR:FR light (R:FR =7.0; FLH) or low R:FR light (R:FR = 1.1; FLL) until cotyledons or the first foliage leaf were fully expanded. Spores of PM were then inoculated onto the leaves, and the seedlings were grown for 7 days (fromcotyledon stage) or 9 days (fromfoliage–leaf stage) under FLH. The number of PM colonies on FLH seedlings was 0.80· (cotyledons) and 0.62· (foliage leaves) the number on FLL seedlings. The reduction on the FLH seedlings was probably the result of changes in leaf morphological characteristics such as a thicker epidermal tissue as a result of the higher R:FR illumination. The number of PM colonies on cotyledons of the FLH seedlings was also smaller than that on seedlings grown under metal-halide lamps providing a spectrum similar to that of natural light (R:FR = 1.2). The ratio of red (600 to 700 nm) to far-red (700 to 800 nm) light of FLH was 7.0 and that of FLL was 1.1. The spectrum of FLH was similar to that of FLL, except in FR (Fig. 1). The spectra were measured with a spectrometer (BLK-CXR-SR; StellarNet, Tampa, FL). View PDF.
Fig. -Light spectra of lamps. FLH = fluorescent lamp with high red-to-far-red ratio (R:FR); FLL = fluorescent lamp with low R:FR; ML = metalhalide lamp that provides a spectrum similar to that of natural light. Relative photon fluxes per unit wavelength are expressed relative to the maximum. The R:FR was estimated by dividing the total photon flux from red light (600 to 700 nm) by that from far-red light (700 to 800 nm).
