SPECTRAL QUALITY AFFECTS DISEASE DEVELOPMENT OF 3 PATHOGENS ON HYDROPONICALLY GROWN PLANTS

Plants mere grown under light-emitting diode (LED) arrays with various spectra to determine the effects of light quality on the development of diseases caused by tomato mosaic virus (ToMV) on pepper (Capsicum a nnuum L.), powdery mildew [Sphaerotheca fuliginea (Schlectend:Fr.) Pol laci] on cucumber (Cucumis sativus L.), and bacterial wilt (Pseudomona s solanacearum Smith) on tomato (Lycopersicon esculentum Mill.). One L ED (660) array supplied 99% red light at 660 nm (25 nm bandwidth at ha lf-peak height) and 1% far-red light between 700 to 800 nm. A second L ED (660/735) array supplied 83% red light at 660 nm and 17% far-red li ght at 735 nm (25 nm bandwidth at half-peak height). A third LED (660/ BF) array supplied 98% red light at 660 nm, 1% blue light (BF) between 350 to 550 nm, and 1% far-red light between 700 to 800 nm. Control pl ants were grown under broad-spectrum metal halide (MH) lamps. Plants m ere grown at a mean photon flux (300 to 800 nm) of 330 mu mol . m(-2). s(-1) under a 12-h day/night photoperiod. Spectral quality affected e ach pathosystem differently. In the ToMV/pepper pathosystem, disease s ymptoms developed slower and were less severe in plants grown under li ght sources that contained blue and UV-A wavelengths (MH and 660/BF tr eatments) compared to plants grown under light sources that lacked blu e and W-A wavelengths (660 and 660/735 LED arrays). In contrast, the n umber of colonies per leaf was highest and the mean colony diameters o f S. fuliginea on cucumber plants were largest on leaves grown under t he MH lamp (highest amount of blue and UV-Alight) and least on leaves grown under the 660 LED array (no blue or UV A light). The addition of far-red irradiation to the primary light source in the 660/735 LED ar ray increased the colony counts per leaf in the S. fuliginea/cucumber pathosystem compared to the red-only (660) LED array. In the P. solana cearum/tomato pathosystem, disease symptoms were less severe in plants grown under the 660 LED array, but the effects of spectral quality on disease development when other wavelengths were included in the light source (MH, 660/BF-, and 660/735-grown plants) were equivocal. These results demonstrate that spectral quality may be useful as a component of an integrated pest management program for future space-based contr olled ecological life support systems.