In vitro morphological and physiological traits of the rootstock GF677 (Prunus persica × P. amygdalus) under different blue–red LED intensities

Light (spectrum, intensity, photoperiod) is one of the most important factors that governs the proliferation of many plant species cultured in vitro. In this study, the in vitro shoot proliferation, photosynthetic pigments, photosystem II photochemistry, and leaf anatomy of the GF677 rootstock (Prunus persica x Prunus amygdalus) were investigated under three light intensities (20, 40 and 120 μmol m⁻² s⁻¹) provided by light-emitting diode (LED) lamps with a 430–690 nm absorption spectrum, emitted mainly by blue (21%) and red (63%) (BR, 1:3). The culture medium used was the MS supplemented with 3.1 μM benzyl adenine, 0.05 μM α-naphthalene acetic acid, 0.3 μM gibberellic acid, 20 g L⁻¹ sucrose (pH .8), and 6 g L⁻¹ Plant Agar (30 days, 16h photoperiod, 22 ± 2 °C). The results showed that shoot multiplication percentages (90.48–92.86%), proliferation rates (new shoots per explant) (1.95–2.10), shoot height (0.52 cm), maximum efficiency of photosystem II (PSII) photochemistry (F_v/F_m), and the efficiency of excitation energy capture by open PSII reaction centers (F_v′/F_m′) were significantly higher under 20 μmol m⁻² s⁻¹ and 40 μmol m⁻² s⁻¹ as compared to 120 μmol m⁻² s⁻¹. Moreover, under 20 μmol m⁻² s⁻¹, the photoprotective energy dissipation (Φ_NPQ), the quantum yield of non-regulated energy loss in PSII (Φ_NO), chlorophyll b (Chl b), total chlorophyll (a + b), and carotenoids were enhanced as compared to 40 μmol m⁻² s⁻¹, whereas the percentage of explants with macroscopically stress appearance symptoms (23.21%) and chlorophyll a/chlorophyll b (Chl a/Chl b) ratio were significantly lower under 20 μmol m⁻² s⁻¹. Leaves grown under 20 μmol m⁻² s⁻¹ exhibited a somehow typical dorsiventral leaf anatomy with distinguishable palisade and spongy parenchyma with more layers of palisade parenchyma as compared to the produced thin leaves with suppressed mesophyll tissue under 40 μmol m⁻² s⁻¹. Based on the results obtained, among the three different intensities tested, 20 μmol m⁻² s⁻¹ is the best and most beneficial lighting condition for GF677 proliferation.