Controlled environments as an Adjunct to Field Research on Lentils (Lens culinaris). III. Photoperiodic Lighting and Consequences for Flowering

Abstract

Six genotypes of lentil (Lens culinaris) were grown in pots in a glasshouse under natural photoperiods of 10-12 h, extended to an inductive photoperiod of 16 h by supplementary illumination from incandescent lamps. The illuminance of the supplementary light was varied by placing replicate pots at different distances from the lamps; it decreased geometrically with distance (i.e. down an illuminance gradient) from about 2000 lux directly beneath the lamps to about 40 lux at a distance of 6 m from them. All genotypes came into flower progressively later as illuminance decreased; those selected in northern temperate regions were especially sensitive, taking about twice as long to flower at an illuminance of 40 compared with 2000 lux. We suggest, however, that these quantitative responses do not reflect differences in sensitivity to illuminance per se, but are the consequences of genotypic differences in sensitivity to photoperiod. The implications of these data are discussed in terms of adaptation to the aerial environment and strategies for screening germplasm and plant breeding in lentils and other grain legumes.Photoperiodically-sensitive plants flower seasonally in response to a particular duration of night. In natural environments the transition to and from darkness is not abrupt, but occurs through a gradually changing intensity of twilight. At what point does the plant begin to respond to darkness, or to light at dawn? Vince-Prue (1975) has considered these questions for plants in general but, to our knowledge (Summerfield, 1981), there are no data on these types of responses in lentils (Lens culinaris L.).Photoperiod is the only environmental factor which changes in an exactly predictable manner at any given latitude throughout every calendar year. These seasonal changes are a powerful determinant of phenological events in many crops of major economic importance, perhaps the best known of which are rice (Vergara and Chang, 1976) and soyabeans (Summerfield and Roberts, 1983a). Those lentil genotypes which respond to differences in photoperiod by coming into flower relatively early or late are described as 'quantitative long-day plants' (they will flower in a wide range of day-lengths but the onset of flowering is especially rapid in longer (16-24 h) than in shorter (6-12 h) days; Summerfield,

Grain Legumes

“…Lentil plants must perceive a particular vernalization, temperature, and photoperiod regime to initiate reproductive growth (Summerfield et al 1984;Erskine et al 1989;McKenzie and Hill 1989). In the case of photoperiod, this response is known to be under genetic control (Summerfield et al 1984).…”

“…In the case of photoperiod, this response is known to be under genetic control (Summerfield et al 1984). However, temperature and vernalization are known to influence the magnitude of the photoperiod response, and this magnitude varies regionally and presumably genetically (Saxena and Wassimi 1984;Erskine 1997).…”

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

“…In an artificial light system when the number of lights installed inside a chamber is limited, the addition of expensive FR bulbs requires the removal of other bulbs, which decreases light intensity. Thus, considerations must be made to optimize both the light intensity [minimum 400-500 μmol m −2 s −1 ; (Summerfield et al 1984;Sager and McFarlane 1997)] and the wavelength distribution received by the plants.…”

“…LD plants, such as lentil, require a lower R: FR ratio for flower induction. The quantity and interception of photosynthetically active radiation (PAR) have been studied in lentil plants (Colli and Facchini 1954;Summerfield et al 1984), but the role of photomorphogenic radiation as a regulator of floral induction of lentil plants under controlled environmental conditions is not clear. Therefore, the main goal of this research was to examine the spectral properties of growth chamber light sources, taking a whole-plant flowering approach by examining growth responses of two typical lentil cultivars in similar growth chambers under different light sources.…”

Understanding photothermal interactions will help expand production range and increase genetic diversity of lentil (Lens culinarisMedik.)

“…Saint-Clair (1972) was the first to demonstrate variation in response to photoperiod between two lentil genotypes, with one showing characteristics of a long day plant, sensitive to changes in photoperiod and not flowering under photoperiods of 14 hours or less, while the other was almost day neutral, flowering under a wide range of photoperiods with less variation than the former. Further studies on photoperiod response in lentil showed that genotypes originating from subtropical regions flowered earliest and were least sensitive to changing photoperiod, suggesting that differences in photoperiod sensitivity may be a component of adaptation to contrasting geographic regions (Summerfield et al, 1984). Using factorial combinations of varying photoperiods and temperatures, (Summerfield et al, 1985) described the rate of progress towards flowering ( 1 / ) for six genotypes as a linear function of temperature and photoperiod with the following two equations:…”