Photosynthetic characteristics of grafted cucumber seedlings following healing and acclimatization under different light spectra and intensities

Utilization of grafted seedlings as the starting plant material for production of cucumber has attracted lots of attention during the last two decades. Good photosynthetic functionality is an important parameter determining the quality of grafted seedlings. In the current study, analysis of biophysical photosynthetic traits as well as the photosynthetic pigments were carried out on grafted cucumber scion on squash seedlings that were exposed to wide ranges of light spectra and intensities. To do so, grafted seedlings were exposed to different light spectra including red (R), blue (B), green (G), white (W), red:far red (R:FR; 70:30), red:blue (R:B in two ratios of 50:50 and 70:30) and four light intensities [25, 50, 100, and 200 µmol m^‑2 s^‑1 photosynthetic photon flux density (PPFD)]. Based on obtained results, exposing grafted seedlings to the highest light intensity (200 µmol m^‑2 s^‑1 PPFD) survival ratio of grafted seedlings except for the seedlings exposed to the combination of R:FR light. Accordingly, the lowest maximum quantum yield of photosystem II (F_v/F_m) was also obtained in grafted seedlings exposed to highest light intensity (200 µmol m^‑2 s^‑1). The maximum F_v/F_m was detected in grafted seedlings under lighting regimes which had B light in their spectrum. By decreasing R light in overall spectrum lower Energy dissipation per reaction center was detected. In combinational light regimes (e.g. W, 70R:30B, and 50R:50B) and G light, the highest Chlorophyll a and b contents were detected under the highest PPFD. Carotenoid content in the light regimes containing B light in their overall spectrum was the highest under 200 µmol m^‑2 s^‑1 PPFD, while in light regimes containing sole R light the lowest carotenoid content was detected under 200 µmol m^‑2 s^‑1 PPFD. In conclusion, combinational R and B lights with an intensity of 50 µmol m^‑2 s^‑1 PPFD can result in best graft taking and photosynthetic performance of grafted cucumber seedlings.