Abstract
Green bean (Phaseolus vulgaris L.) is one of the most important sources of vegetable proteins in the world and it is cultivated all year round, but the light availability, during the dark season, limited its growth. Nevertheless, recent studies conducted on greenhouse horticulture demonstrated that, with the application of light emitting diodes (LEDs) as supplementary light (SL) technology, it is possible to overcome this limitation. Consequently, during the experiment conducted, two cultivars of green bean (‘Saporro’ and ‘Maestrale’) were grown with a soilless system in a cold greenhouse during the fall-winter period. To increase the photoperiod and the daily light integral (DLI), early in the morning, four hours of red (R), blue (B) and red+blue (R + B) supplementary light were supplied by LEDs at 180 μmol·m−2·s−1 (PPFD) at plants level. Plants grown under LEDs improved the yield and the gas exchange system compared with the plants grown under natural light; when B light was supplied as a sole source of SL, it increased the dry matter content and the brightness (L*) of the pods. Between the cultivars, ‘Maestrale’ produced 20 g∙plant−1 of pods more than ‘Saporro’ but the latter’s colour was brighter (L*) and greener (a*), and ‘Saporro’ also showed the highest photosynthetic efficiency (ΦPSII). In conclusion, ‘Maestrale’ and ‘Saporro’ obtained encouraging out-of-season yields under different LED spectra, but among those B light seems to improve overall crop performances and pods quality.
Highlights
Green bean (Phaseolus vulgaris L.) is the most consumed grain legume in the world and has an important role in human diet, due to its high protein and mineral content [1]
The plants with supplementary light emitting diodes (LEDs) lighting produced, on average, 19% more than the control, without showing significant differences between spectra (Table 1)
The height of the plants was modulated by the light, with the plants under LEDs that were higher than those of the control (3 cm on average—Table 1)
Summary
Green bean (Phaseolus vulgaris L.) is the most consumed grain legume in the world and has an important role in human diet, due to its high protein and mineral content [1]. Supplemental light (SL) was proposed (and used) merely to provide light energy for photosynthesis, most of the time considering a priority high fluence rate, to provide the photosynthetic photon flux density (PPFD), and low-cost operation [2], using conventional light sources, especially fluorescent, metal halide, high-pressure sodium (HPS), and incandescent lamps for cultivating plants indoors [3,4]. Such lamps, HPS ones, were reported to be not economically feasible [5] and sometimes to have technical limitations. The emissions of HPS, in some phases of plant growth, are different from those emitted by sunlight and from the values required for photosynthesis, both in terms of spectrum and energy [5,6]
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