ABSTRACT: Light spectra influence growth, development, and quality of plants and seedlings, that is one of the main aspects engaging the interests of private and public researchers and nursery industries. Propagation of hazelnut (Corylus avellana L.), which in the past has been held in low consideration because of the widespread use of rooted suckers directly collected in the field, today is taking on increasing interest due to the strong expansion of hazelnut cultivation. In order to improve the quality of plants and seedlings in greenhouse acclimatization, the effects of light emitting diodes (LED) lights during the ex vitro growth of two hazelnut cultivars (Tonda di Giffoni and Tonda Gentile Romana) were investigated. Plantlets were maintained in a growth chamber and exposed to three different continuous spectrum LED systems as a primary source of illumination and to fluorescent lamps used as control. LEDs differed in the percentage of some wavelength ranges in the spectrum, being AP673L rich in green and red wavelengths, NS1 in blue and green light, G2 in red and far red wavelengths. After a 4-week experimental period, morphometric, biochemical, and histological analyses were carried out. Shoot and leaf growths were influenced by LEDs more than by fluorescent lamps in both cultivars. G2 positively affected biomass increment more than the other LEDs, by inducing not only cell elongation (increase in shoot length, new internodes length, leaf area) but also cell proliferation (increase in new node number). G2 exposure had negative effects on total chlorophyll content but positively affected synthesis of flavonoids in both varieties; therefore, plants grown under this LED showed the lowest nitrogen balance index. Leaf morpho-anatomical analyzed traits (thickness, palisade cell height, number of chloroplasts, number of palisade cells), were influenced especially by G2 and, to a less extent, by NS1 light. Significant differences in some parameters were observed between the two cultivars in response to a same light source. The results obtained underline the importance of light modulation for hazelnut, providing useful information for ex vitro growth of hazelnut plantlets.
