Cost reduction in the micropropagation of banana by using tubular skylights as source for natural lighting

Summary Daylight instead of artificial light was exploited for the in vitro culture of banana. Tubular skylights rediverted natural light into an interior enelosed room whereby each skylight, available for ca. US$600, could sufficiently illuminate an area of 3–5 m². The maintenance-free system allowed only a minimum of heat transfer and no cooling was necessary. The culture room required no electricity supply and under our conditions savings on costs for electricity of US$6 m⁻² wk⁻¹ were achieved, as compared to a standard growth room equipped with artificial lighting and controlled photoperiod and temperature regimes. Under natural light conditions, micropropagated plantlets were well developed at mean photosynthetic photon flux densities (PPFD) of 5–13 μmol m⁻² s⁻¹ and photoperiods of 9–14 h. Micropropagation rates were either the same or significantly higher than under artificial lighting. Single shoots on rooting medium showed some symptoms of etiolation, yet acclimatization rates averaged 95%. A step-like culture rack. rather than a vertical one, permitted uniform plant growth on all levels. This paper describes an established micropropagation system of low cost and simplicity.