Low red: Far-red light ratio causes faster in vitro flowering in lentil

Artificial light in growth chambers typically has a higher red to far-red (R:FR) ratio compared with natural light. This higher ratio may delay flowering and reduce plant height in some long-day plants. Modification of light spectral quality to lower than the critical threshold of R:FR for a given plant species can have important implications with respect to plant structural and physiological traits. The objective of this study was to accelerate lentil (Lens culinaris) flower induction in growth chambers re-fitted with T5 fluorescent bulbs, using supplemental FR bulbs to re-balance the R:FR ratio. Lentil cultivars CDC Greenland and CDC Maxim were grown under three light sources differing in R:FR, namely light emitting diodes (LED; R:FR = 3.09), T5 fluorescent bulbs (R:FR = 5.6), and T5 supplemented with near far-red bulbs (R:FR = 3.1). All three light sources provided 500 mu mol m(-2) s(-1) of photosynthetic photon flux (PPF). Lentil floral induction was significantly affected by the R:FR ratio. Plants grown under R:FR ratios of 3.1 or less flowered 10-11 d earlier than plants grown under an R:FR ratio of 5.6. Both cultivars had the same response to R:FR ratio in terms of days to flowering and flowering rate.