Abstract
The effects of the photosynthetic photon flux density (PPFD) and concentration of culture solution on the growth of strawberry (Fragaria×ananassa Duch. cv. Houko-uwase) plantlets rooted by the direct ex-vitro rooting method were examined. In the direct ex-vitro rooting method, the shoot elongation, rooting, and acclimatization of the plantlets are simultaneously achieved in the controlled environment. In this study, explants of micropropagated shoots were directly inserted into the rockwool plugs and cultured inside the environmental control unit by hydroponics using a culture solution at three different concentrations (0.5U : 1/2 strength of Enshi (Hori, 1966) component of culture solution for hydroponics, 0.2U : 1/5 strength of Enshi component, 0/0.2U : 0 (0-10th days) and 1/5 (11-30th days) strength of Enshi component) under high and low PPFDs (high PPFD : 180μmol m-2 s-1, low PPFD : 70μmol m-2 s-1).
After 30 days in culture, dry and fresh weights, leaf area, number of leaves, and dry weight ratio of the plantlets were measured. All these parameters were greater in a high PPFD than in a low PPFD. The shoot/root ratio was larger in a low PPFD than in a high PPFD. In a high PPFD, growth (dry and fresh weights, etc.) of plantlets was in the order of 0.5U>0.2U>0/0.2U. In a low PPFD, the effect of the concentration of culture solution on the growth of plantlets was not as obvious as that in a high PPFD.
