Photoperiod Extension Research Articles

Extended light exposure increases stem digestibility and biomass production of switchgrass.

Switchgrass is a photoperiod-sensitive energy grass suitable for growing in the marginal lands of China. We explored the effects of extended photoperiods of low-irradiance light (7 μmol·m-2·s-1, no effective photosynthesis) on the growth, the biomass dry weight, the biomass allocation, and, especially, the stem digestibility and cell wall characteristics of switchgrass. Two extended photoperiods (i.e., 18 and 24 h) were applied over Alamo. Extended light exposure (18 and 24 h) resulted in delayed heading and higher dry weights of vegetative organs (by 32.87 and 35.94%, respectively) at the expense of reducing the amount of sexual organs (by 40.05 and 50.87%, respectively). Compared to the control group (i.e., natural photoperiod), the yield of hexoses (% dry matter) in the stems after a direct enzymatic hydrolysis (DEH) treatment significantly increased (by 44.02 and 46.10%) for those groups irradiated during 18 and 24 h, respectively. Moreover, the yield of hexoses obtained via enzymatic hydrolysis increased after both basic (1% NaOH) and acid (1% H2SO4) pretreatments for the groups irradiated during 18 and 24 h. Additionally, low-irradiance light extension (LILE) significantly increased the content of non-structural carbohydrates (NSCs) while notably reducing the lignin content and the syringyl to guaiacyl (S/G) ratio. These structural changes were in part responsible for the observed improved stem digestibility. Remarkably, LILE significantly decreased the cellulose crystallinity index (CrI) of switchgrass by significantly increasing both the arabinose substitution degree in xylan and the content of ammonium oxalate-extractable uronic acids, both favoring cellulose digestibility. Despite this LILE technology is not applied to the cultivation of switchgrass on a large scale yet, we believe that the present work is important in that it reveals important relationships between extended day length irradiations and biomass production and quality. Additionally, this study paves the way for improving biomass production and digestibility via genetic modification of day length sensitive transcription factors or key structural genes in switchgrass leaves.

Influence of high latitude light conditions on sensory quality and contents of health and sensory-related compounds in swede roots (Brassica napus L. ssp. rapifera Metzg.).

Vegetable growers in Arctic areas must increasingly rely on market strategies based on regional origin and product quality. Swede roots (rutabaga) were grown in a phytotron to investigate the effect of high latitude light conditions on sensory quality and some health and sensory-related compounds. Experimental treatments included modifications of 24 h natural day length (69° 39' N) by moving plants at daily intervals to dark chambers with either no light, fluorescent growth light and/or low intensity photoperiod extension. Shortening the photosynthetic light period to 12 h produced smaller roots than 15.7 h and 18 h, with highest scores for bitter and sulfur taste, and lowest scores for sweetness, acidic taste and fibrousness. The photoperiod in combination with the photosynthetic light period also had an influence on glucosinolate (GLS) contents, with lowest concentrations in 24 h natural light and highest in 12 h natural light. Concentrations of vitamin C, glucose, fructose and sucrose were not significantly influenced by any of the treatments. High latitude light conditions, with long photosynthetic light periods and 24 h photoperiod, can enhance sweet/less bitter taste and reduce GLS contents in swede roots, compared to growth under short day conditions. This influence of light conditions on eating quality may benefit marketing of regional products from high latitudes. © 2017 Society of Chemical Industry.

Chitosan oligosaccharide addition affects current-year shoot of post-transplant Buddhist pine (Podocarpus macrophyllus) seedlings under contrasting photoperiods

Abstract: Chitosan oligosaccharides (COS) have been used as modifiers to promote growth and mineral nutrient utilization in crop plants, but its over-year effect on current-year shoot (CYS) of juvenile trees is still unclear. In this study, Buddhist pine (Podocarpus macrophyllus) seedlings were cultured under natural and extended photoperiods with or without COS addition for one year. In the following spring, parameters of leaf length, biomass accumulation, and N content in CYS were found to be increased by COS addition under the extended photoperiod. P concentration of COS-treated seedlings was lower under longer photoperiod, but both N and P concentrations were negatively correlated with leaf length and biomass accumulation, suggesting the utilization of N and P for growth demand of CYS. The sole addition of COS mainly resulted in whole-plant P accumulation. However, when combined with the extended photoperiod, COS addition showed over-year effect on biomass accumulation and N content in CYS of transplanted Buddhist pine seedlings. Further studies are needed to confirm these results on other tree species.

Effects of Photoperiod Extension on Clock Gene and Neuropeptide RNA Expression in the SCN of the Soay Sheep.

In mammals, changing daylength (photoperiod) is the main synchronizer of seasonal functions. The photoperiodic information is transmitted through the retino-hypothalamic tract to the suprachiasmatic nuclei (SCN), site of the master circadian clock. To investigate effects of day length change on the sheep SCN, we used in-situ hybridization to assess the daily temporal organization of expression of circadian clock genes (Per1, Per2, Bmal1 and Fbxl21) and neuropeptides (Vip, Grp and Avp) in animals acclimated to a short photoperiod (SP; 8h of light) and at 3 or 15 days following transfer to a long photoperiod (LP3, LP15, respectively; 16h of light), achieved by an acute 8-h delay of lights off. We found that waveforms of SCN gene expression conformed to those previously seen in LP acclimated animals within 3 days of transfer to LP. Mean levels of expression for Per1-2 and Fbxl21 were nearly 2-fold higher in the LP15 than in the SP group. The expression of Vip was arrhythmic and unaffected by photoperiod, while, in contrast to rodents, Grp expression was not detectable within the sheep SCN. Expression of the circadian output gene Avp cycled robustly in all photoperiod groups with no detectable change in phasing. Overall these data suggest that synchronizing effects of light on SCN circadian organisation proceed similarly in ungulates and in rodents, despite differences in neuropeptide gene expression.

Photoperiod extension effect on nursery tray-plants of everbearing strawberry

Photoperiod extension effect on nursery tray-plants of everbearing strawberry

Characterization of Ppd-D1 alleles on the developmental traits and rhythmic expression of photoperiod genes in common wheat

Photoperiodic response is an important characteristic that plays an important role in plant adaptability for various environments. Wheat cultivars grow widely and have high yield potential for the strong photoperiod adaptibility. To assess the photoperiodic response of different genotypes in wheat cultivars, the photoperiodic effects of the Ppd-D1 alleles and the expressions of the related TaGI, TaCO and TaFT genes in Liaochun 10 and Ningchun 36 were investigated under the short-day (6 h light, SD), moderate-day (12 h light, MD) and long-day (24 h light, LD) conditions. Amplicon length comparison indicated that the promoter of Ppd-D1 in Ningchun 36 is intact, while Liaochun 10 presented the partial sequence deletion of Ppd-D1 promoter. The durations of all developmental stages of the two cultivars were reduced by subjection to an extended photoperiod, except for the stamen and pistil differentiation stage in the Liaochun 10 cultivar. The expression levels of the Ppd-D1 alleles and the TaGI, TaCO and TaFT genes associated with the photoperiod pathway were examined over a 24-h period under SD and MD conditions. The relationships of different photoperiodic responses of the two cultivars and the expression of photoperiod pathway genes were analyzed accordingly. The photoperiod insensitive (PI) genotype plants flower early under SD; meanwhile, the abnormal expression of the Ppd-D1a allele is accompanied with an increase in TaFT1 expression and the TaCO expression variation. The results would facilitate molecular breeding in wheat.

Effects of light quality on the flowering responses inKalanchoe blossfeldiana

Light is one of the most important environmental factors and has at least three aspects; intensity, photoperiod and quality. There are many studies of the influences of light intensity and the photoperiod on flowering responses. Those results led to the development of novel practical technology for the control of flowering. However, there are many still unexplained phenomena on the light quality. Kalanchoe (Kalanchoe blossfeldiana Poellniz.) is well known as a typical qualitative (obligate) short-day (SD) plant and it has been used as experimental material for the flowering response. Thus, the flowering responses of two cultivars of kalanchoe, 'Arena' and 'Cora', were studied under the following light regimes: SD under four different light emitting diodes (LEDs), white, blue, green and red; SD under natural light + light extension (LE; 7 h from midnight); SD under natural light + photoperiod extension (12 h; 6:00-18:00) with supplementary LED lighting (four colours as above). In the case of LE, the flowering was completely inhibited under each light quality. Under SD, the earliest flowering occurred under red light. Blue light considerably delayed flowering. In contrast, photoperiod extension (to the critical photoperiod for kalanchoe) with blue light caused a distinct flowering response but there was no flowering under supplementary red and green light. It is concluded that the flowering of kalanchoe is mainly controlled by red light. The direct flowering response to blue light was weak but blue light had a secondary or indirect effect.

Incidence of Footpad Dermatitis and Hock Burns in Broilers as Affected by Genotype, Lighting Program and Litter Type

Abstract The aim of this study was to define the conditions for improving broiler leg health, thus ultimately promoting broiler welfare and greater economic efficiency of production, by investigating the effects of litter type, lighting program, or genetic predisposition on the incidence and severity of footpad dermatitis and hock burns. The study was conducted on broiler genotypes (G) Hubbard Classic and Ross 308. Litter (L) was either chopped straw or wood shavings. Lighting programs (LP) were applied when broilers were eight days old. One lighting program (LP1) was designed so that chicks between 8 to 39 days of age were exposed to 16L:4D:2L:2D, and received 23L:1D between 40 to 42 days of age. The other lighting program (LP2) was a gradual extension of photoperiod after restrictions in the second week: 16L:8D (8-14 days), 16L:3D:2L:3D (15-21 days), 16L:2D:4L:2D (22-28 days), 16L:1D:6L:1D (29-35 days) and 23L:1D (36-42 days). Evaluations of footpad lesions and hock burn, according to the method described by Thomas et al. (2004), were carried out individually for each bird, on days 21 and 42. Based on the average score and the frequency of the worst forms of footpad dermatitis, better growing conditions for broilers were found when wood shavings were used as litter material rather than the chopped straw (P<0.01), and when a lighting program with gradual lengthening of photoperiod and with intermittent light/ dark periods (LP2) was applied, compared to a moderate-constant photoperiod lighting program (LP1) (P<0.01). The Ross 308 broiler genotype, despite its lower body weight, showed a greater tendency to develop footpad dermatitis and hock burns. Hock burns developed more slowly than footpad dermatitis, and thereby, would be likely to exhibit a smaller adverse effect on broiler welfare and quality of chicken feet.

Post-flowering photoperiod and radiation interaction in soybean yield determination: Direct and indirect photoperiodic effects

Soybean (Glycine max (L.) Merrill) exposure to long days during the post-flowering phase increases total biomass, nodes, pods and seeds per plant, and also the post-flowering duration, increasing the radiation offer. This work aims to identify the main mechanisms responsible for yield increases in response to long days, separating direct photoperiodic effects on yield determination, from the indirect effect associated with changes in cumulative radiation when the crop cycle is modified by photoperiod. Two field experiments were conducted with an indeterminate soybean cultivar. A factorial combination of two radiation levels (unshaded and shaded), and two or three photoperiod regimes (control, extended 1.5 and 3h) was imposed from flowering to maturity. Yield tended to be reduced by shade and increased by extended photoperiod mainly through their effects on nodes per m2, and thereby affecting pods and seeds per m2. Photoperiod extension increased node number due to both increased cumulative radiation (indirect effect) and delayed reproductive development (direct effect). As a result, more pods were established per unit of cumulative radiation under extended photoperiod. The results suggest that photoperiod extension enhanced yield radiation use efficiency due to the alleviation of intra-nodal interferences. The direct post-flowering photoperiodic effect on node number and the resultant effects on pod and seed number, provide evidence of direct photoperiodic effects on soybean yield determination.

Effects of an extended photoperiod on gonadal function and condition of hair coats in Thoroughbred colts and fillies

ABSTRACTThe effects of an extended photoperiod (EP) in Thoroughbreds colts and fillies from winter at one year old to spring at two years old on the gonadal functions, coat condition, and endocrine changes were investigated. Sixty-two Thoroughbreds (31 colts and 31 fillies) reared in the Hidaka Training and Research Center (Hidaka), Japan Racing Association were used. Thirty of them (15 colts and 15 fillies) were reared under EP conditions from December 20 to April 10, and the remaining 32 horses were reared under natural light alone as a control group. For EP, a 100-watt white bulb was set near the ceilings of stalls, and lighting conditions of 14.5-hr light and 9.5-hr dark periods were established. Blood was collected from the jugular vein once a month from October at one year old to February at two years old in both colts and fillies, and then twice a month in colts and weekly in fillies after March, and the coat condition was evaluated in January and April in 56 horses. To investigate endocrine changes, the plasma concentrations of prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), immunoreactive (ir-) inhibin, testosterone, estradiol-17β and progesterone were measured. No significant difference was noted in the coat condition between the two groups in January, but they changed from winter to summer coats (molting of winter coats) in April in the EP group compared with the control group. Regarding endocrine changes, the plasma concentrations of prolactin, FSH, ir-inhibin and testosterone were significantly higher in the EP colts than in the control group from January to April. The plasma concentrations of LH tended to rise in the EP colts from January to April compared with the control group. In the EP fillies, the plasma concentrations of prolactin, LH, ir-inhibin, estradiol-17β and progesterone were significantly higher during January and April, but a significantly high level of FSH was noted in the control than EP group in January. The ovulation day was advanced in the EP fillies compared with the control group. The present study clearly demonstrated that EP treatment during rearing advanced the molting of winter coats in both colts and fillies. These results suggested to be due to the action of prolactin being increased by EP treatment. In addition, EP treatment stimulated the hypothalamus-pituitary-gonadal axis even in yearlings, and advanced ovulation in fillies. Since EP treatment-induced changes in the yearlings were within the physiological range, and the method is safe and simple, EP treatment may be an effective technique in horse husbandry.

Different effects of an extended photoperiod treatment on growth, gonadal function, and condition of hair coats in Thoroughbred yearlings reared under different climate conditions.

ABSTRACTOne- to two-year-old Thoroughbred colts and fillies being reared in Miyazaki (warm climate) and Hidaka (cold climate), Japan, were administered extended photoperiod (EP) treatment between December 20 and the following April 10, and its effect on growth, endocrine changes, gonadal activation, and hair coat condition was investigated. In colts reared in Miyazaki, no effect of EP treatment was noted on the growth indices, including body weight (BW), height at withers (HW), girth, and cannon circumference (CC), whereas the BWs and CCs of fillies were significantly higher in the EP treatment group than the control. In Hidaka, the BWs and HWs of colts and HWs of fillies were significantly higher in the EP treatment group. Gonadal activation characterized by an increase in circulating hormone concentrations was earlier in the EP treatment group for fillies reared in Miyazaki [luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone (P4), and estradiol-17β (E2)] and in colts (LH, testosterone, and E2) and fillies (LH, FSH, P4, and E2) reared in Hidaka. Regardless of sex and climate, prolactin was significantly higher in the EP treatment group, whereas insulin-like growth factor (IGF-I) was not. Initial ovulation occurred before April in more of the EP treatment group than the control regardless of the climate. Molting of the hair coat, examined in March, was advanced in the EP treatment group regardless of sex and climate. These results suggest that EP treatment may promote growth and gonadal activation in fillies reared in Miyazaki and in colts and fillies reared in Hidaka and that the effect may be mediated by prolactin.

Promoting effects of an extended photoperiod treatment on the condition of hair coats and gonadal function in Thoroughbred weanlings.

ABSTRACTThe effects of an extended photoperiod (EP) treatment (14.5 hr light, 9.5 hr dark) on Thoroughbred colts and fillies from December 25 at 7–9 months old to the following May at 12–14 months old on coat condition and gonadal functions were investigated. Coat condition was evaluated in April. The colts and fillies in the EP treatment group changed from winter to summer coats (molting of winter coats), whereas those in the control group did not. To determine the day of first ovulation, the plasma concentrations of progesterone were measured once a month in fillies. The day of first ovulation was advanced in the EP treatment fillies compared with the control fillies. The present study clearly demonstrated that the EP treatment advanced the molting of winter coats and advanced ovulation in fillies, even in weanlings.

Photoperiod sensitivity of local millet and sorghum varieties in West Africa

Photoperiod has a strong impact on the development of local millet and sorghum varieties which are two of the most important staple food crops for millions of people in West Africa. Therefore, a better understanding of the response to photoperiod is needed in order to improve production and ultimately increase yield. Several studies have demonstrated the importance of the adaptive capability of local varieties, especially in coping with environmental stress conditions. The objective of this study was to determine the photoperiod sensitivity (PS) characteristics of the most common local varieties of millet and sorghum in Burkina Faso, West Africa. Planting date experiments consisting of 5 or 6 planting dates with complementary irrigation and fertilizer to avoid water and nitrogen stress effect on phenology were conducted at the experiment station of Di in northwestern Burkina Faso during the rainy seasons of 2003, 2004, 2006 and 2007. The study included 7 millet and 11 sorghum varieties from the three main agroecological zones in Burkina Faso to determine their sensitivity to photoperiod. In addition to the various key phenological parameters, panicle initiation date was measured in 2007. Therefore, thermal time from emergence to PI and photoperiod at PI could be experimentally determined. After evaluation of the relation between the PI stage and the other stages that could easily be observed, thermal time from emergence to flag leaf expansion was used to determine the date of panicle initiation (PI) as well as the photoperiod at PI for the experiments conducted from 2003 to 2006. Then, a graphical analysis was conducted to define the critical threshold photoperiod and photoperiod sensitivity for each variety. For both millet and sorghum, the photoperiod sensitivity ranged from 142 to 6184 growing degree days (GDDh−1) per hour of photoperiod extension. The critical photoperiod (Pc) ranged from a daylength of 13.00 to 13.35h. Although these experiments were only conducted at one location, this study showed that photoperiod response is not only related to latitude, but depends also on the capability of lowlands to maintain soil moisture. There was a positive correlation between the critical photoperiod (Pc) and the latitude of origin of the local varieties and a negative correlation between photoperiod sensitivity and the latitude of origin. Further work will include the implementation of these results in crop simulation models for yield forecasting and the determination of crop management alternatives for millet and sorghum in West Africa

Effect of exponential fertilization on growth and nutritional status in Buddhist pine (Podocarpus macrophyllus [Thunb.] D. Don) seedlings cultured in natural and prolonged photoperiods

Slow growth rate limits the development of seedlings from the Podocarpaceae family. The extended photoperiod (EP) is well known to promote tree seedling growth, but it may also cause the possibility of nutrient dilution without a proper nutrient supply regime. Exponential fertilization (EF) has been proven to counter nutrient dilution within tree seedlings efficiently. However, no study has determined the response of Podocarpus seedlings to the interaction of EF and photoperiod. We fed 13-month old Buddhist pine (Podocarpus macrophyllus [Thunb.] D. Don) seedlings using EF applied at rates of 0 (control), 50 (E50), 100 (E100), and 150 (E150) mg nitrogen (N) seedling−1 for 5 months, during which half of all seedlings were cultured in the natural photoperiod (NP) with the others exposed to EP. The longer photoperiod resulted in greater seedling height and biomass accumulation of Buddhist pine seedlings. Relative to NP, EP increased N content at the whole-plant level but decreased N concentration in the stem and root, which indicated the symptom of N dilution. However, both phosphorus (P) content and P concentration increased in response to the longer photoperiod. EF rates in the E100 and E150 treatments were evaluated to be the ‘sufficiency’ ones for both N and P in EP and NP, respectively. In conclusion, EP could stimulate the growth of Buddhist pine seedlings but caused N dilution within them at the same time, and photoperiod would change the nutritional response of these seedlings to EF.

Flowering regulation in the facultative biennial Oenothera biennis L.: Environmental effects and their relation to growth rate

The lifecycle of the facultative biennial oilseed-crop evening primrose (Oenothera biennis) is a major constraint for its commercial production under different growing conditions, as a variable proportion of plants fails to flower during the first season and remains as vegetative rosettes (biennial behavior). The aim of this work was to understand how flowering is regulated in this species and to identify the main determinants of its biennial behavior.Different planting dates and manipulative treatments (seed vernalization, photoperiod extension and fertilization) were employed to analyze if: (i) biennial behavior occurs when obligate requirements for vernalization or photoperiod are not satisfied; and (ii) responses to these environmental cues depend on the size and/or growth rate of rosettes.Our results indicate that O. biennis has an obligate long-day requirement for flowering and a facultative vernalization response. There is no minimum size requirement for vernalization response (as very small seedlings responded to the vernalization treatment) and the rate of development toward flowering under inductive photoperiods was strongly affected by rosette's growth rate. The incidence of high temperatures just before the onset of reproduction is proposed as an inhibitory factor that prevents reproduction under otherwise photo-inductive conditions. This last factor would explain the high incidence of biennial behavior frequently observed in spring/summer sowing in this crop.

A quantitative trait locus for long photoperiod response mapped on chromosome 4H in barley

Photoperiod response is a key determinant for barley adaptation to diverse environments. A major quantitative trait locus (QTL) for response to long photoperiod was identified in Australia (Perth, 31°56′S) and China (Wuhan, 30°33′N) using 178 doubled haploid lines derived from a cross of an Australian barley, Baudin, and a Canadian barley, AC Metcalfe. The QTL was detected as a major QTL in the 18-h photoperiod glasshouse experiments and mapped to the Xp12m50B199–Xp13m47B399 interval on chromosome 4H with a LOD score of 57 in Australia and confirmed in China. The single QTL accounted for 77.48 and 37.81% of phenotypic variation for long photoperiod response in Australia and China, respectively. The same QTL also controlled heading date in Australia, under normal and extended photoperiod conditions, and in China, under extended photoperiod and late-sown conditions. The QTL advanced heading date by 27.8 days in Australia and 42.5 days in China under a 18-h photoperiod. In addition, QTL for heading date were identified on chromosomes 2H and 3H. The chromosome 3H QTL was associated with the denso gene and detected in all conditions, but the chromosome 2H QTL was only detected in Australia. The new photoperiod response QTL, Qhea.BM.4-13/Qpho.BM.4-13, on chromosome 4H and its associated markers will provide an alternative for plant breeders developing new varieties for different environments using marker-assisted selection.

Effect of Photoperiod on Gonadal Steroid Hormone Levels and Reproductive Cycles of Northern Fur Seals (Callorhinus ursinus)

The northern fur seal (Callorhinus ursinus) is a migratory marine mammal belonging to the family Otariidae that breeds on the islands in the North Pacific Ocean, Bering Sea, Sea of Okhotsk, and near the coast of California during summer (Peterson 1968; Gentry 1998). Their reproduction is characterized by extreme polygyny and highly synchronized annual cycles that are concentrated around the boreal summer (Peterson 1968; Trites 1992; Gentry 1998). Females arrive at breeding sites in early July, give birth within 36 hours, and then enter estrus and copulate within a few days (Peterson 1968). Although active gestation persists for approximately eight months, the total duration of gestation period is approximately one year because of the embryonic diapause (delayed implantation), which accurately synchronizes the annual reproductive cycle (Craig 1964; Boyd 1991). Males return to the breeding sites approximately one month before females, establish their territories in the breeding area, and maintain breeding activities for approximately two months (Peterson 1968). Photoperiod is commonly cited as the main trigger for the synchronization of the annual reproductive cycles of pinnipeds (Boyd 1991; Atkinson 1997; Boyd et al. 1999), and this theory is supported by several studies. Temte (1985) compared the mean dates of parturition between the two wild populations of northern fur seals in Alaska (57°N) and California (33°N) and suggested that a mean photoperiod of 12.5 h/day in autumn acts as a trigger for the termination of embryonic diapause and initiation of implantation to synchronize parturition (also see Spotte and Adams 1981). Kiyota et al. (2009) also observed a significant latitudinal variation in the parturition of captive northern fur seals in Japan, which supported the theory of photoperiodic control of the reproductive cycle. The effect of photoperiod on reproductive cycles has been only experimentally demonstrated in harbour seals (Phoca vitulina) (Bigg and Fisher 1975). Bigg and Fisher (1975) demonstrated that estrus occurred earlier than usual during extended photoperiods and was delayed during shortened photoperiods. However, Daniel (1981) did not detect any effect of a shortened photoperiod on the rate of blastocyst development in northern fur seals. Boyd (1991) interpreted the finding of Daniel’s study to be the result of the relatively insignificant shortened photoperiod and/or the short study period. Seasonal changes that occurred in the testicular activity of male fur seals in captivity corresponded with those that occurred in males in the wild (Kohyama et al. 1999; Tsubota et al. 2001). These studies indicate that photoperiodic control of the male reproductive cycle is similar to that of female reproductive cycle, but this photoperiodic effect has not been extensively studied (Boyd 1991). Photoperiod has been reported to control the timing of implantation and parturition in pinnipeds (Temte 1985). However, this interpretation has not been applied to the timing of estrous and ovulation of non-pregnant females or the testicular activities of males. Other mammals, such as Siberian hamsters (Phodopus sungorus) and gray mouse lemurs (Microcebus murinus), are defined as long-day breeders because their reproductive activities increase in response to day length as the seasons change from spring to summer (Goldman 1991, 1999; Perret and Aujard 2001). Therefore, we aimed to determine whether the reproductive cycles of both female and male northern fur seals would be altered under experimentally induced conditions of extended photoperiods. Seasonal changes in gonadal steroid hormone levels and body weight were used as indicators of the reproductive cycle indices, because changes in these factors in relation to the reproductive cycle have previously been described (Kiyota et al. 1999; Kohyama et al. 1999). The effects of photoperiod on seasonal changes in reproductive cycles

Variability of duration of pre-anthesis phases as a strategy for increasing wheat grain yield

In wheat, stem elongation phase (SEP) duration is critical for grain number (GN) per unit of area determination, as it is the phase in which the spikes grow. Lengthening SEP, for instance by photoperiodic sensitivity, without altering the cycle to anthesis (AT) has been proposed as an alternative way to increase spike dry weight, and in turn GN. As most works supporting this idea have modified only SEP by artificial manipulation (e.g. photoperiod extensions), it is relevant to evaluate this hypothesis in populations segregating for this attribute in natural conditions. The aim of this work was to analyse the variability in SEP duration relative to AT in two F4 populations; in order to select contrasting phenotypes to evaluate the impact of this attribute on grain yield components and to analyse the selection response of this attribute. These segregating populations (Las Rosas INTA × Triguero 230 (A) and Klein Estrella × ProINTA B. Alazán (B)) were derived from parental lines with similar flowering time but different relative duration of their pre-anthesis phases. Two field experiments with previous vernalization treatment in cool chamber were carried out. In 2006, F4 populations were characterized and from one of them (population B, which presented higher variability) four groups were selected, which presented contrasting phenotypes in the attribute under study. Progenies of these groups (F5), together with remnant F4 full-sib of each one, were studied during 2007. Grain yield per plant was higher, due to GN increases, when duration of the SEP was lengthened. However, selection response to longer SEP with similar cycle to AT could not be found, possibly as the result of a high environmental influence on this attribute. The phenotypic variability evidenced in this attribute was not clearly associated with major adaptation genes evaluated (i.e. Ppd and/or Vrn), suggesting that other minor genes could be associated.

Modelling environmental effects on phenology and canopy development of diverse sorghum genotypes

The ability to predict phenology and canopy development is critical in crop models used for simulating likely consequences of alternative crop management and cultivar choice strategies. Here we quantify and contrast the temperature and photoperiod responses for phenology and canopy development of a diverse range of elite Indian and Australian sorghum genotypes (hybrid and landrace). Detailed field experiments were undertaken in Australia and India using a range of genotypes, sowing dates, and photoperiod extension treatments. Measurements of timing of developmental stages and leaf appearance were taken. The generality of photo-thermal approaches to modelling phenological and canopy development was tested. Environmental and genotypic effects on rate of progression from emergence to floral initiation (E-FI) were explained well using a multiplicative model, which combined the intrinsic development rate ( R opt), with responses to temperature and photoperiod. Differences in R opt and extent of the photoperiod response explained most genotypic effects. Average leaf initiation rate (LIR), leaf appearance rate and duration of the phase from anthesis to physiological maturity differed among genotypes. The association of total leaf number (TLN) with photoperiod found for all genotypes could not be fully explained by effects on development and LIRs. While a putative effect of photoperiod on LIR would explain the observations, other possible confounding factors, such as air–soil temperature differential and the nature of model structure were considered and discussed. This study found a generally robust predictive capacity of photo-thermal development models across diverse ranges of both genotypes and environments. Hence, they remain the most appropriate models for simulation analysis of genotype-by-management scenarios in environments varying broadly in temperature and photoperiod.

Photoperiod Sensitivity of Rhizoma Peanut Germplasm

Short days are thought to alter dry matter (DM) partitioning in rhizoma peanut (Arachis glabrata Benth.). Under controlled environmental conditions, six lines of rhizoma peanut germplasm (cultivars Florigraze and Arbrook; Florida lines Ecoturf, Arbrook Select, and Arblick; and PI 262826) were exposed to natural and extended photoperiod regimes (15 or 18 h). The study started 21 Sept. 2000 and ran until the following May; aboveground DM was harvested five times. The following year the same lines were transplanted into the field, where they received either natural light or 15 h extended photoperiod conditions between 20 Sept. 2001 and 19 Apr. 2002 and again during the winter of 2002–2003. In the field, cover and DM was determined on approximately 9 wk intervals. In the controlled environment study, both extended photoperiod treatments increased DM yield, but the 18 h treatment was most consistent across selections and dates. The February response was greatest when there was greater than fivefold increase across selections for the 18 h treatment above natural photoperiod (2.80 vs. 0.52 g/pot, respectively). In the field, percent cover was enhanced by extended photoperiod for all selections except Ecoturf by the second sampling date after the lights were turned on (avg. 90 vs. 38% cover, respectively, for extended and natural photoperiod). Cover differences persisted until June 2002. Dry matter yield also was increased by treatment during the fall of both years. These studies suggest that selection for late and early season DM production in rhizoma peanut will select for photoperiod insensitivity.