Natural Short Days Research Articles

Increasing the Nighttime Lighting Duration Can Hasten Flowering of Long-day Plants

Low-intensity (≈2 μmol·m−2·s−1) photoperiodic lighting is often delivered at night to promote flowering of long-day greenhouse ornamentals when natural daylengths are short. An intermediate far-red (FR) fraction [percentage of FR light in red (R) + FR light] is necessary for the most rapid flowering in some crops, including snapdragon (Antirrhinum majus) and petunia (Petunia ×hybrida), compared with a low FR fraction. Specialty light-emitting diodes (LEDs) that include R+FR light with an intermediate FR fraction are effective at floral promotion but cost-prohibitive, whereas common warm-white (WW) LEDs with a low FR fraction can delay flowering. Because the duration to saturate flowering is longer than currently used (e.g., 4 to 8 hours) for some long-day plants, we conducted a replicated greenhouse experiment to determine how the WW or R+FR LED lighting duration influenced flowering. We grew snapdragon ‘Liberty Classic Yellow’, petunia ‘Easy Wave Burgundy Star’, and petunia ‘Wave Purple Improved’ under truncated 8-h natural short days with or without WW or R+FR (1:1) LEDs operating for 0, 4, 8, 12, or 16 hours in the middle of each night throughout the experiment. Snapdragon flowered 13 to 16 days earlier (21% to 28% earlier) under R+FR LEDs than under WW LEDs regardless of the lighting duration. Increasing the lighting duration from 0 to 16 hours decreased flowering time by up to 16 days and decreased plant height and leaf number at flowering under R+FR LEDs but not under WW LEDs. For petunia ‘Easy Wave Burgundy Star’, although WW LEDs delayed flowering by 6 to 13 days but promoted lateral branching compared with R+FR LEDs, the gap in flowering time narrowed as the lighting duration increased from 4 to 16 hours. Increasing the lighting duration improved the efficacy of WW LEDs but not R+FR LEDs. Flowering of petunia ‘Wave Purple Improved’ was unaffected as the lighting duration increased from 4 to 16 hours regardless of the lamp type and was delayed by 6 to 10 days under WW LEDs than under R+FR LEDs. For both petunia cultivars, flowering time was similar under 16-hour WW LEDs and 4-hour R+FR LEDs. In conclusion, increasing the nighttime lighting duration increased the efficacy of WW LEDs at promoting flowering of petunia and increased the efficacy of R+FR LED lamps at promoting flowering of snapdragon. Delivering WW LEDs all night long can minimize flowering delay in petunia compared with R+FR LEDs. In contrast, an intermediate FR fraction was indispensable to promote flowering of snapdragon, for which WW LEDs were ineffective.

Methyltransferase 1 (OsMTS1) interacts with hydroxycinnamoyltransferase 1 (OsHCT1) and promotes heading by upregulating heading date 1 (Hd1)

Heading date determines the distribution and yield potentials of rice, and is an ideal target for crop improvement using CRISPR/Cas9 genome editing system. In this study, we reported the loss-of-function of Methyltransferase 1 (MTS1), which promotes heading in rice. Here, we constructed knockouts and overexpression transgenic plants of OsMTS1 in ZH8015 and Nipponbare (NIP) for the first time to validate its heading date function in rice subspecies Oryza sativa ssp. Indica and O. Sativa ssp. Japonica, respectively. The OsMTS1 knockouts in ZH8015 and NIP rice significantly promoted heading date under both natural short days (NSD) and natural long days (NLD) conditions, while the overexpression of OsMTS1 significantly delayed heading date in ZH8015 and NIP rice under both NSD and NLD conditions. Likewise, the complementation transgenic plants displayed late heading date phenotype. OsMTS1 repressed heading through up-regulating Heading date 1 (Hd1) and down-regulating Early heading date 1 (Ehd1) and Heading date 3a (Hd3a). The OsMTS1 protein interacted with OsHCT1 proteins using a yeast two-hybrid (Y2H) assay. The Y2H and overexpression confirmed that OsMTS1 interacted with OsHCT1, which delayed heading by 4.7 days under NLD. Taken together, CRISPR/Cas9, genetic complementation, and overexpression results validated that OsMTS1 represses heading in Indica and Japonica rice under both NLD and NSD conditions. These results demonstrated that OsMTS1 is a useful target for breeding early maturing rice varieties by CRISPR/Cas9 gene editing of the functional allele.

Daily Light Integral, but Not the Photoperiod, Influences the Time to Flower and Finished Quality of Dianthus Specialty Cut Flowers

Because of the burgeoning year-round demand, greenhouse growers across the United States are increasingly becoming interested in producing specialty cut flowers for local and regional markets. However, outdoor or high tunnel production is not possible year-round in northern latitudes because of low temperatures and radiation intensities experienced during the winter and early spring. Additionally, natural short days in these seasons can limit which photoperiodic crops can be grown. Thus, our objectives were to quantify the influence of the photoperiod and daily light integral (DLI) on greenhouse-grown dianthus ‘Amazon Neon Cherry’ and ‘Amazon Rose Magic’ (Dianthus barbatus interspecific) cut flowers during the young plant and finishing stages. Seeds of both cultivars were sown under 9-, 10-, 11-, 12-, 13-, 15-, or 16-hour photoperiods and a DLI of either ≈5 or 10 mol⋅m−2⋅d−1. After 4 weeks, seedlings from several young-plant photoperiods were distributed across 11-, 12-, 13-, 14-, 15-, or 16-hour photoperiods or a 4-hour night interruption (NI) under a DLI of either ≈5 (low) or 14 (moderate) mol⋅m−2⋅d−1 for finishing. The young plant photoperiod generally had a statistical, but not commercial, influence on development and finished cut flower quality, whereas a 16-h finishing photoperiod marginally hastened development compared with an 11-hour finishing photoperiod. Additionally, stems were 11 to 13 cm longer when finished under the 16-hour photoperiod compared with those finished under the 11-hour photoperiod. Day length minimally influenced the time to flower and harvest, indicating a day-neutral flowering response. However, plants finished under a moderate DLI reached visible flower bud and were harvestable 9 to 10 days earlier than those finished under a low DLI. Additionally, ≈99% of cut flowers finished under a moderate DLI were harvestable, whereas only up to 32% and 57% of dianthus ‘Amazon Rose Magic’ and ‘Amazon Neon Cherry’, respectively, finished under a low DLI were harvestable. Although finished stem lengths were comparable between DLI treatments, cut flower stems were up to 29.6% thicker under a moderate DLI. These findings indicate that high-quality greenhouse-grown dianthus ‘Amazon Neon Cherry’ and ‘Amazon Rose Magic’ cut flowers can be produced when grown under any photoperiod between 9 and 16 hours for 4 weeks (during the young plant stage) and finished under any photoperiod between 11 and 16 hours or a 4-hour NI during finishing. If longer stems are desired, then plants can be finished under a 16-hour photoperiod. Young plants should be grown under a moderate DLI ≥10 mol⋅m−2⋅d−1 to promote biomass accumulation and reduce the young plant crop time. Additionally, plants should be finished under a moderate DLI ≥14 mol⋅m−2⋅d−1 to reduce crop time and increase stem thickness and yield.

EN LOS CABRITOS MACHOS DE REGIONES SUBTROPICALES, LA EXPOSICIÓN A DÍAS LARGOS ARTIFICIALES ESTIMULA UNA MAYOR TASA CRECIMIENTO, UN MEJOR DESARROLLO E INCREMENTA LA GLUCEMIA

<p><strong>Background.</strong> Small ruminants from subtropical regions are sensitive to respond physiologically to natural photoperiodic changes. In some subtropical goat production systems as located in semi-arid areas of México, the main objective is to obtain in the shortest possible time, males with a suitable weight and body development for sale. <strong>Objective.</strong> The present study determines if the exposure to artificial long day photoperiod could promote a growth rate, body development and an increased glycemia in male goat kids compared with those under natural short days. <strong>Methodology.</strong> Starting on late September, 21 creole male goat kids (13 ± 0.1 week aged; mean ± SEM) were assigned to one of the two experimental groups. In the natural short days group, males remain under natural short days from autumn-winter (GDC, n = 10). In the artificial long days group, males were exposed to artificial photoperiod consisting in 16 h light and 8 h darkness (GDL, n = 11). The study lasted until the animals had 35 weeks of age. All animals were fed according their nutritional requirements. <strong>Results.</strong> During the study, the body weight of the GDL animals was higher than that of the GDCN males (P < 0.05). Due to this, the daily weight gain (GDP) obtained at 23 weeks of age was higher in the GDL males (165 g/day) than that registered in the GDC males (143 g/day; P <0.05). In some periods, the males of the GDL had higher body mass index (IMC) than the males of the GDC (P < 0.05). Thoracic perimeter at week 32 was greater in the GDL males than in the GDC males (P <0.05). The height at the withers did not reach significant differences in the comparisons between groups in the different weeks measured (P > 0.05). However, the total height at the withers gained during the study was significantly higher in the GDL males than in the GDC males (P < 0.01). Under fasting conditions, GDL males had higher levels (P < 0.05) of blood glucose in some periods than GDC males. <strong>Implications.</strong> The present study demonstrate that artificial long days stimulates growth in goats as occurs in other ruminants<strong>. Conclusion.</strong> Exposure of the male goat kids from subtropical regions to artificial long days, promotes a higher growth rate, better body development and increased glycemia compared to kids maintained under natural short-day photoperiods.</p>

Effect of Photoperiod, Propagative Material, and Production Period on Greenhouse-grown Ginger and Turmeric Plants

The objectives were to 1) compare growth and yield of different ginger (Zingiber officinale) and turmeric (Curcuma longa) propagules grown under two photoperiods (Expt. 1); and 2) evaluate whether their growing season could be extended with night interruption lighting (NI) during the winter (Expt. 2). In Expt. 1, propagules included 1) micropropagated tissue culture (TC) transplants, 2) second-generation rhizomes harvested from TC transplants (2GR), and 3) seed rhizomes (R). Plants received natural short days (SDs) or NI providing a total photon flux density (TPFD) of 1.3 µmol·m−2·s−1. Providing NI increased number of new tillers or leaves per plant, rhizome yield (i.e., rhizome fresh weight), and dry mass partitioning to rhizomes in both species. There was no clear trend on SPAD index in response to photoperiod or propagative material. Although TC-derived plants produced more tillers or leaves per plant, 2GR ginger and R turmeric produced a higher rhizome yield. In Expt. 2, seed rhizomes of ginger and turmeric were grown under five treatments with different photoperiods and/or production periods: 1) 20 weeks with NI (20NI), 2) 24 weeks with NI (24NI), 3) 28 weeks with NI (28NI), 4) 14 weeks with NI + 10 weeks under natural SDs (24NISD), and 5) 14 weeks with NI + 14 weeks under natural SDs (28NISD). NI provided a TPFD of 4.5 µmol·m−2·s−1. Lengthening the production period and providing NI increased rhizome yield and crude fiber content in both species. SPAD index decreased when plants were exposed to natural SDs at the end of the production period (NISD treatments). Results demonstrate the potential to overcome winter dormancy of ginger and turmeric plants with NI, enabling higher rhizome yield under natural SDs.

In dual-purpose subtropical goats, 1 h of extra-light given from 16 to 17 h after dawn (pulse of light) in winter stimulates milk yield.

This research communication addresses the hypothesis that in dual-purpose goats, exposure to 1 h of extra-light given from 16 to 17 h after dawn (pulse of light) in winter stimulates milk yield. One group of goats was maintained under natural short photoperiod (natural day; ND (n = 7)). Another group of lactating females was submitted to an artificial long-day photoperiod consisting of 16 h light and 8 h darkness (long days; LD (n = 7)). A third group of females received one single hour of extra-light 16 h after the fixed dawn (pulse of light; PL (n = 6)). Goats from LD and PL yielded 30% more milk than goats from ND. Mean percentages of fat, protein and lactose contents in milk did not differ between the 3 groups at any stage of lactation, but these components in grams/day were higher in goats from PL than in the others two groups within the first 45 d of lactation. In conclusion, dual-purpose lactating goats that started their lactation during natural short days, the daily exposition to a 1-h pulse of light is sufficient to stimulate milk yield compared to females maintained under natural short photoperiod.

Promotion of Flowering from Far-red Radiation Depends on the Photosynthetic Daily Light Integral

Under natural short days, growers can use photoperiodic lighting to promote flowering of long-day plants and inhibit flowering of short-day plants. Unlike traditional lamps used for photoperiodic lighting, low-intensity light-emitting diode (LED) lamps allow for a wide array of adjustable spectral distributions relevant to regulation of flowering, including red (R) and white (W) radiation with or without far-red (FR) radiation. Our objective was to quantify how day-extension (DE) photoperiodic lighting from two commercially available low-intensity LED lamps emitting R + W or R + W + FR radiation interacted with daily light integral (DLI) to influence stem elongation and flowering of several ornamental species. Long-day plants [petunia (Petunia ×hybrida Vilm.-Andr. ‘Dreams Midnight’) and snapdragon (Antirrhinum majus L. ‘Oh Snap Pink’)], short-day plants [african marigold (Tagetes erecta L. ‘Moonsong Deep Orange’) and potted sunflower (Helianthus annuus L. ‘Pacino Gold’)], and day-neutral plants [pansy (Viola ×wittrockiana Gams. ‘Matrix Yellow’) and zinnia (Zinnia elegans Jacq. ‘Magellan Cherry’)] were grown at 20/18 °C day/night air temperatures and under low (6–9 mol·m−2·d−1) or high (16–19 mol·m−2·d−1) seasonal photosynthetic DLIs from ambient solar radiation combined with supplemental high-pressure sodium lighting and DE LED lighting. Photoperiods consisted of a truncated 9-hour day (0800–1700 hr) with additional 1-hour (1700–1800 hr, 10 hours total), 4-hour (1700–2100 hr, 13 hours total), or 7-hour (1700–2400 hr, 16 hours total) R + W or R + W + FR LED lighting at 2 μmol·m−2·s−1. Days to visible bud, plant height at first open flower, and time to first open flower (TTF) of each species were influenced by DLI, lamp type, and photoperiod though to different magnitudes. For example, plant height of african marigold and potted sunflower at first open flower was greatest under R + W + FR lamps, high DLIs, and 16-hour photoperiods. Petunia grown under R + W lamps, high DLI, and 10- and 13-hour photoperiods were the most compact. For all species, TTF was generally reduced under high DLIs. For example, regardless of the lamp type, flowering of african marigold occurred fastest under a high DLI and 10-hour photoperiod. Flowering of petunia and snapdragon occurred fastest under a high DLI, R + W + FR lamps, and a 16-hour photoperiod. However, only under high DLIs, R + W or R + W + FR lamps were equally effective at promoting flowering when used to provide DE lighting. Our data suggest that under low DLIs, flowering of long-day plants (petunia and snapdragon) occurs more rapidly under lamps providing R + W + FR, whereas under high DLIs, flowering is promoted similarly under either R + W or R + W + FR lamps.

Investigating the efficacy of white light-emitting diodes at regulating flowering of photoperiodic ornamental crops

Under natural short days (SDs), low-intensity lighting during the middle of a night (night interruption, NI) can control flowering of daylength-sensitive ornamentals. Red (R, 600-700 nm) and far-red (FR, 700-800 nm) radiation is primarily absorbed by phytochromes that mediate flowering, whereas blue (B, 400-500 nm) radiation typically has less photoperiodic relevance, at least at a low intensity. White (W) light-emitting diodes (LEDs) emit photons over a broad spectrum; however to our knowledge, their efficacy at regulating flowering has not been published. We investigated whether white LEDs controlled flowering of five long-day plants [calibrachoa (Calibrachoa × hybrida), coreopsis (Coreopsis grandiflora), petunia (Petunia × hybrida), rudbeckia (Rudbeckia hirta), and snapdragon (Antirrhinum majus)] and two SD plants [chrysanthemum (Chrysanthemum × morifolium) and marigold (Tagetes erecta)]. Plants were grown in a greenhouse at 20°C under 9-h SDs with or without 4-h NIs from R, B+R, cool-W, warm-W, or R+W+FR LEDs. Irradiance at plant canopy was adjusted to approximately 2 µmol m-2 s-1 between 400 and 800 nm. Compared with SD, all NIs similarly promoted flowering of calibrachoa and rudbeckia; however, only R+W+FR promoted flowering of snapdragon. NIs without FR radiation (i.e., R, B+R, cool-W, and warm-W) accelerated flowering of coreopsis and petunia, but flowering under R+W+FR was 11-16% earlier than under the other NIs. R+W+FR was less effective than the other NIs at inhibiting flowering of chrysanthemum and marigold. Cool-W and warm-W had similar effects on flowering and development of all crops. Plant height of calibrachoa, coreopsis, and marigold at flowering was greatest under R+W+FR; however, stem length of the other crops was similar under all NIs. We conclude that W LEDs inhibited flowering of SD plants and were as effective as R or R+W+FR radiation at promoting flowering of some, but not all, long-day plants.

Controlling Flowering of Photoperiodic Ornamental Crops with Light-emitting Diode Lamps: A Coordinated Grower Trial

Photoperiodic lighting from lamps with a moderate ratio of red [R (600–700 nm)] to far-red [FR (700–800 nm)] light effectively promotes flowering of long-day plants (LDPs). Because of spectral controllability, long life span, and energy efficiency, light-emitting diodes (LEDs) have emerged as an alternative to conventional light sources, such as incandescent (INC) and high-pressure sodium (HPS) lamps. We conducted a coordinated trial with five commercial greenhouse growers to investigate the efficacy of R + white (W) + FR LEDs, with an R:FR of 0.82, to regulate flowering of daylength-sensitive ornamental crops. The trial was also performed in two replicate greenhouses at Michigan State University (MSU). Ageratum (Ageratum houstonianum), calibrachoa (Calibrachoa ×hybrida), dahlia (Dahlia ×hybrida), dianthus (Dianthus chinensis), petunia (Petunia ×hybrida), snapdragon (Antirrhinum majus), and verbena (Verbena ×hybrida) were grown under natural short days (SDs) with 4-hour night-interruption (NI) lighting provided by the R + W + FR LEDs or conventional lamps typically used by each grower. Two companies used HPS lamps, whereas the other sites used INC lamps. In addition, a natural SD treatment, a truncated 9-hour SD treatment, or a compact fluorescent lamp (CFL) NI treatment was provided at three different sites. With few exceptions, time to flower and flowering percentage of the bedding plant crops tested were similar under the R + W + FR LEDs to that under the conventional lamps at all sites. At MSU, ageratum, dianthus, petunia, snapdragon, and verbena flowered earlier under NI lighting treatments than under 9-hour SDs. In addition, plant height and visible flower bud or inflorescence number at flowering were similar under the R + W + FR LEDs and INC lamps for most crops. Therefore, we conclude that the R + W + FR LEDs are as effective as lamps traditionally used in greenhouses at controlling flowering of photoperiodic plants.

Traitements photopériodiques et reproduction chez les animaux d'élevage

Photoperiodic treatments and reproduction in farm animals. Farm animal productions are frequently tied to the seasons, which explain the seasonal variations in availability of fresh animal products (meat, milk, cheese and eggs). Among farmed species, fishes and birds are generally considered as more directly sensitive to external factors (mainly temperature in fish and photoperiod in birds). Artificial photoperiodic treatments are widely used in numerous species including mammals ; they consist in providing extra-light during natural short days (chickens, turkeys, guinea fowl, sheep and goats), or in the administration of melatonin during long days (goats, sheep). These measures help adjust the breeding season to the requirements of the breeder and/ or cancel completely seasonal variations of sperm production in semen production centres (mammals) as well as in poultry and fish farms. Additionally, pure light treatments (without melatonin), especially when there is outside access, are non invasive and preserve the animals’ integrity and welfare.

Seasonality of Reproduction in Mammals: Intimate Regulatory Mechanisms and Practical Implications

Farm mammals generally express seasonal variations in their production traits, thus inducing changing availability of fresh derived animal products (meat, milk and cheese) or performances (horses). This is due to a more or less marked seasonal birth distribution in sheep and goats, in horses but not cattle. Birth peak occurs at the end of winter-early spring, the most favourable period for the progeny to survive. Most species show seasonal variations in their ovulation frequency (presence or absence of ovulation), spermatogenic activity (from moderate decrease to complete absence of sperm production), gamete quality (variations in fertilization rates and embryo survival), and also sexual behaviour. The intimate mechanism involved is a complex combination of endogenous circannual rhythm driven and synchronized by light and melatonin. Profound and long-term neuroendocrine changes involving different neuromediator systems were described to play a role in these processes. In most species artificial photoperiodic treatments consisting of extra-light during natural short days (in sheep and goats and mares) or melatonin during long days (in sheep and goats) are extensively used to either adjust the breeding season to animal producer needs and/or to completely overcome seasonal variations of sperm production in artificial insemination centres. Pure light treatments (without melatonin), especially when applied in open barns, could be considered as non-invasive ones which fully respect animal welfare. Genetic selection could be one of the future ways to decrease seasonality in sheep and goats.

Shasta Daisy Cultivars Respond Differently to Photoperiod and Vernalization

Abstract Inconsistencies have been reported in the role of vernalization and photoperiod on growth and flowering of Leucanthemum x superbum Bergmans ex J. Ingram cultivars. Five cultivars were used to determine the effects of vernalization and photoperiod on days to flower, shoot height, growth index, flower shoot number, and quality rating. Plants received 0, 3, 6, 9, or 12 weeks of vernalization time (VER) at 4.4C (40F) and afterward were placed under either natural short days (SD) or night-interrupted lighting (NIL) in a greenhouse. ‘Becky’ showed an obligate requirement for NIL to flower with 100% of plants flowering under NIL and 0% of plants flowering under SD regardless of VER. Vernalization for 6 weeks before NIL increased shoot height, growth index, flower shoot number, and quality rating but the fewest days to flower occurred after 12 weeks of VER. ‘Silver Princess’, ‘Snow Cap’, ‘Snow Lady’, and ‘Summer Snowball’ showed a facultative requirement for NIL to flower. Plants under NIL flowered earlier, were larger, had more flower shoots, and had a higher overall quality rating than plants under SD. Shoot height and growth index were highest under NIL after 3 and 6 weeks of VER, flower shoot number was highest after 3 to 9 weeks of VER, but days to flower was least after 12 weeks of VER. Therefore, NIL after 3 or 6 weeks of VER would maximize plant size and quality for practical application in the cultivars studied but result in more DTF when compared to 12 weeks of VER.

Seasonality of reproduction and production in farm fishes, birds and mammals

A very large majority of farm animals express seasonal variations in their production traits, thus inducing seasonal availability of fresh derived animal products (meat, milk, cheese and eggs). This pattern is in part the consequence of the farmer's objective to market his products in the most economically favourable period. It may also be imposed by the season-dependent access to feed resources, as in ruminants, or by the specific requirements derived from adaptation to environmental conditions such as water temperature in fish. But seasonal variations in animal products are also the consequence of constraints resulting from the occurrence of a more or less marked seasonal reproductive season in most farm animal species including fish, poultry and mammals. Like their wild counterparts, at mid and high latitudes, most farm animals normally give birth at the end of winter-early spring, the most favourable period for the progeny to survive and thus promote the next generation. As a consequence, most species show seasonal variations in their ovulation frequency (mammals and fish: presence or absence of ovulation; birds: variations or suppression of laying rates), spermatogenic activity (from moderate to complete absence of sperm production), gamete quality (variations in fertilisation rates and embryo survival), and also sexual behaviour. Among species of interest for animal production, fishes and birds are generally considered as more directly sensitive to external factors (mainly temperature in fish, photoperiod in birds). In all species, it is therefore advisable that artificial photoperiodic treatments consisting of extra-light during natural short days (in chickens, turkeys, guinea fowl, sheep and goats) or melatonin during long days (in goats, sheep) be extensively used to either adjust the breeding season to animal producer needs and/or to completely overcome seasonal variations of sperm production in artificial insemination centres (mammals) and breeder flock operations (poultry, fish farming). Pure light treatments (without melatonin), especially when applied in open barns, could be considered as non invasive ones which fully respect animal welfare.

Physical Mapping and Chromosomal Location of the Photoperiod Response Gene Ppd2 in Common Wheat

Duration from sowing to flowering is of critical importance for crop adaptation. Breeding for the optimal flowering time is one of the major factors, which confer maximal yields in a given environment. The timing of flowering is modulated primarily by responsiveness to photoperiod and temperature, and there are large differences in sensitivity among genotypes. In most spring wheat cultivars the duration of the vegetative period is strongly influenced by genes controlling photoperiod response. In this paper we report the photoperiod responses of a set of ‘Chinese Spring’ substitution and partial deletion lines of homoeologous group 2 chromosomes studied under natural short days. We confirmed the presence of dominant genes Ppd1 and Ppd2 on chromosomes 2D and 2B, respectively, and compared the effects of Ppd1 and Ppd2 for daylength response. The photoperiodic responses of partial chromosome deletion lines of ‘Chinese Spring’ allowed us to map Ppd2 physically between breakpoints 0.27 and 0.53 of the short arm of chromosome 2B. This result is consistent with the finding of a possible location of Ppd2 based on molecular marker studies. A dosage effect of the dominant gene Ppd2 was shown.

Involvement of abscisic acid (ABA) in bulb dormancy of Allium wakegi Araki I. Endogenous levels of ABA in relation to bulb dormancy and effects of exogenous ABA and fluridone

Allium wakegi plants exposed to long days (LD, 14 h-photoperiod) developed bulbs, which were dormant from the 30th to the 125th day of LD, but those grown under natural short days (SD) did not develop bulbs. The contents of abscisic acid (ABA) in both whole bulbs and buds of the bulbs increased in LD, reaching a maximum at the 60th day of LD and decreasing thereafter, but those in basal leaf sheaths (this part corresponds to a bulb after bulb development) and buds did not increase in SD. The ABA content was related to the depth of bulb dormancy. Application of 500 μM ABA to bulbs for 24 h significantly delayed sprouting, but that of 5 or 50 μM ABA had little or no effect. Application of 25 or 125 μM fluridone to the soil just before exposure to LD bleached new expanding leaves and reduced bulb size, but had no effect on the development of bulb scales that characterize bulb formation. The bulbs formed under such conditions sprouted earlier than those of control plants. The levels of endogenous ABA in bulbs, buds of the bulbs, leaf blades, and roots were reduced by fluridone application. These results indicate that ABA plays an important role in bulb dormancy of Allium wakegi.

CuSO 4 filters influence flowering of Chrysanthemum cv. Spears

`Spears' chrysanthemums ( Dendranthema × grandiflorum [Ramat.] Kitamura) were grown under solar filters filled with CuSO 4 in solution which absorbs FR, or water, which does not absorb FR, and were exposed to marginally long natural photoperiods, artificially long photoperiods, or artificially short photoperiods. Internode length and plant height were reduced under CuSO 4 filters compared to plants grown under water filters, regardless of photoperiod. Plants grown under water- or CuSO 4–filled filters that received artificial short days flowered 7 days ahead of the plants grown in natural, marginally long photoperiods under CuSO 4 filters and 17 days ahead of the plants grown under water filters and receiving natural, marginally long photoperiods. The number of nodes was the same for the plants grown in short and marginally long days under CuSO 4 filters and in short days under water filters, indicating that flower induction occurred simultaneously in these treatments. Development of additional nodes on plants under water-filled filters and receiving natural long-days indicated that floral induction was delayed. A cool white fluorescent light night break prevented or delayed flowering of plants grown under water- and CuSO 4–filled filters during natural short days. The results demonstrate that standard practices of photoperiodic control can be used to time chrysanthemums `Spears' grown under CuSO 4 filters for pot mum production.

FLOWERING IN PIGEONPEA IN KENYA: SENSITIVITY TO PHOTOPERIOD AND TEMPERATURE DURING PRE-FLOWERING DEVELOPMENT

Plants of the photoperiod-sensitive, late-maturing pigeonpea (Cajanus cajan) cv. KAT777 were grown in pots in modified field environments at Katumani, Kenya. They were transferred at different durations after emergence from natural short days (SD, 12.6 h d−1) to artificially-extended long days (LD, 15.0 h d−1), and vice versa, under both ambient (19 °C) and warmer (26 °C) temperatures created beneath p olythene enclosures. All plants at 19 °C flowered within 106–160 d after emergence whereas only those transferred from LD to SD flowered at 26 °C during the investigation (202 d). A well-defined photoperiod-insens itive pre-inductive phase (a1) was detected after emergence; it lasted for 26 d at 19 °C but increased to 49 d at 26 °C. Thereafter, SD hastened and LD delayed progress to flowering until a third pha se, the photoperiod-insensitive post-inductive phase (a3) of pre-flowering development. At 19 °C, a3 was 66 d while the duration of the inductive phase in SD (IS) was 25 d and in LD (IL) it was 72 d. Plants were also moved from ambient to warmer temperatures and vice versa within either SD or LD at different durations after emergence. In SD all plants flowered during the investigation ( 250 d) whereas in LD only the plants transferred from the warmer to the ambient temperature regime flowered. During the initial stages of development plants were less sensitive to supra-optimal temperatures so that developmental progress from emerg ence to first flowering was the same whether plants were held at warmer or ambient temperatures during the first 35 d from emergence. Furthermore, plants transferred from the ambient to the warmer temperature in SD at any time from 49 to 77 d from emergence flowered at similar times to those kept at ambient temperature from emergence. Since a1 = 26 d and a1 + IS = 51 d, we sugg est that these results imply that exposure to supra-optimal temperature in SD during the latter 60% of the photoperiod-sensitive inductive phase (IS) of pre-flowering development delayed progress to flowering. In contrast, expos ing plants to supra-optimal temperature during either the photoperiod-insensitive pre-inductive phase (a1) or part of the photoperiod-insensitive post-inductive phase (a3) or during the first 40% of the photo period-sensitive inductive phase did not delay progress to flowering.

The Response of Long-day Herbaceous Perennials to a Night-interruption at Low Night Temperatures

A 4-hr night interruption (NI) is an effective way to promote flowering in many long-day herbaceous perennials. Some perennials are grown outdoors in the early spring and often are exposed to low night temperatures. Long days delivered by NI lighting ineffectively promote flowering under low-temperature conditions in some long-day species. The objective of this experiment was to determine the effectiveness of NI long-day lighting treatments delivered at different night temperatures in promoting flowering of several herbaceous perennials. Ten herbaceous perennial species were grown under natural short days augmented with a 4-hr NI. Night temperatures were 2.5, 5, 10, 15, 20, and 25°C with day temperature of 25°C for all treatments. Plants were transferred to 9-hr days at a constant 20°C after 7 weeks of treatment. Results on flowering percentage, date of visible bud and flowering, node count, flower bud count, and plant height at flowering will be presented.

Flowering control of Ixodia achillaeoides

Ixodia achillaeoides, a native of south Australia, is a potentially excellent cut flower that can be used in floral arrangements. The plant was found to require relatively low temperatures for flowering (< 17 °C). Long days reduced the time to flower initiation and sped up development. However, under these conditions, flower initiation occurred only on terminal shoots, while axillary shoots did not develop and remained vegetative. Under both natural short days (starting from October) and controlled short days, flowering time was delayed, but both lateral and terminal shoots developed and bloomed and thus many more flowers were formed. Growing ixodia plants first under short days and then under long days decreased time to flowering but reduced the number of flowers as compared with continuous short days. When plants were first grown under long days and then under short days, flower initiation occurred earlier (as compared with continuous short days), but not anthesis. The number of flowers formed with this treatment was similar to that found under continuous short days.

The Differences in the Effects of Low Temperature and Day Length on the Flowering within Seed-Propagated Dianthus spp. and Cultivars

Seed-propagated annual dianthuses, D. ×Mikadonadeshiko, D. barbatus, D. superbus var. longicalicinus, and D. japonicus, are grown for cut flowers in Japan. Investigations on the flowering behavior in responses to chilling and to day length in these dianthuses were carried out.D. ×Mikadonadeshiko and D. barbatus have a cold requirement for flowering as their representative cultivars Miss Biwako and Kurokawawase, and required exposure to natural chilling till mid-December for flower bud formation and stem elongation. Plants grown above 14°C remained vegetative, exhibiting no vernalizing effect.Long day length (LD) promoted flowering and stem elongation for the suboptimally or optimally vernalized plants, LD had no effect on flower bud initiation in non-vernalized plants. Nonvernalized plants initiated flower buds under natural short days during the winter.On the other hand, D. superbus var. longicalicinus and D. japonicus showed no cold requirement and were day neutral for flowering. Rosetted growth in winter was caused simply by low temperature which regresses stem elongation.Dianthus spp. which require low temperature possess a juvenile phase lasting 9 weeks from seeding by which time 9 to 10 leaf pairs are produced on the main stem. Seed ver-nalization was ineffective for these cultivars.In the youngest plants capable of being stimulated by low temperature, only the main stem bolted; the lateral shoots which were immature during vernalization remained vegetative even after vernalization. This demonstrated that the action of cold on flowering was limited to mature shoots.The differences in cold requirement among the six D. barbatus cultivars was also observed. The ever-flowering cv Kyakko required no chilling, whereas others, such as cv Arima, required 9 or more weeks of chilling at 5°C to flower.