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Flowering is a crucial phase in hemp cultivation. It influences both stem and seed yield. A uniform and short flowering duration in hemp is desirable, because it favors uniform crop development. Moreover, flowering is often taken as a reference point for harvesting, and very long durations of flowering might mislead the operator in judging the proper time for mowing. In this article, a large dataset of flowering time and duration for different monoecious and dioecious varieties was studied and the effect of sowing time and genotype on flowering duration is discussed. Minimal flowering duration was observed when the time from emergence to flowering was short. This, was related however, to low yields. Dynamics of flowering was accurately described by a bi-logistic curve that indicates the presence of two underlying logistic processes.
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... Hemp is classified as a qualitative short-day plant that flowers in response to shortening photoperiods. Hemp development occurs over a continuum that may be classified into juvenile (vegetative), photoperiod inductive (vegetative and flowering), and harvest maturity (anthesis) stages (Amaducci et al. 2008a;Hall et al. 2012;Lisson et al. 2000). After emergence, hemp plants typically have a short vegetative phase, also referred to as a "juvenile phase." ...
... Small (2015) noted that flowering in hemp was highly dependent on the latitude for which it was adapted, with populations selected for far northern latitudes flowering and producing seeds shortly after planting. Hall et al. (2012) (Amaducci et al. 2008a;Hall et al. 2012). Therefore, plantings may be limited to late spring and summer when daylength allows for adequate vegetative growth before flowering. ...
... Therefore, plantings may be limited to late spring and summer when daylength allows for adequate vegetative growth before flowering. Although the impact of temperature and photoperiod has been investigated in hemp grown for fiber or seed production (Amaducci et al. 2008a(Amaducci et al. , 2008b(Amaducci et al. , 2012Tang et al. 2016), there is less information on the impact of environmental conditions on flower yield in hemp. Some hemp plants exhibit a dayneutral flowering trait. ...
... This aspect in hemp is important and has been one of the most studied traits in this species. Diverse models and experimental investigations aimed at determining the factors controlling the flowering in hemp have been carried out (Amaducci et al. 2008b;Amaducci et al. 2008c;Amaducci et al. 2012;Cosentino et al. 2012;Hall et al. 2012;Hall et al. 2013;Hall et al. 2014b;Lisson et al. 2000a;Lisson et al. 2000b;Salentijn et al. 2019;van der Werf et al. 1994a). Being a shortday plant, hemp flowering is induced at short photoperiods. ...
... 2.2) of carbon assimilation and biomass production. The precocity to flowering is a trait under strong genetic control in hemp (Amaducci et al. 2008b;Salentijn et al. 2015). In a given environment, different hemp genotypes display wide variability in flowering time. ...
... In a given environment, different hemp genotypes display wide variability in flowering time. Hemp flowering has been successively modeled by Lisson et al. (2000aLisson et al. ( , 2000b and Amaducci et al. (2008b). Both groups described the post-emergent phenology of hemp as a succession of 3 phases: (i) a juvenile phase (Basic Vegetative Phase -BVP) during which flowering does not occur even under low photoperiod conditions, (ii) a Photoperiod-Induced Phase (PIP) during which the duration of the daylength may induce flowering if the daylength decreases under a critical photoperiod: the maximum optimum photoperiod (MOP) and (iii) a Flower-Development Phase (FDP) occurring between flowering initiation and the appearance of the first flower. ...
Chapter
Hemp is a crop that in recent years has received renewed attention and been cultivated in numerous countries after having been abandoned by many during the twentieth century. This ‘rebirth’ is due to numerous factors: its favorable agronomical characteristics, its image of being a sustainable crop, and the plasticity of the products it can provide. However, due to its absence for a long time, there is a lack of expert knowledge on cultivating hemp. There is a lack of scientific knowledge regarding the specificities of its biology, and the strong interaction between genotype and environment remains a limiting factor of hemp cultivation, affecting both the yield and quality of the biomass produced. In this chapter, we have discussed the ins and outs of the cultivation of hemp through a scientific prism to address the principal factors, environmental and genotypic, that drive the agronomical characteristics of a hemp crop. Thereafter, we have focussed on the best crop management practices for optimizing hemp cultivation in terms of yield and quality parameters of the different fractions of the biomass that hemp can provide.KeywordsAgronomyCrop managementCultivationEcophysiologyIndustrial hemp
... Cannabis sativa is a quantitative short-day plant where decreasing daylength (often) regulates flowering initiation (van der Werf et al., 1994). Amaducci et al. (2008b) redefined hemp as a 'qualitative' short-day plant due to its continuous dynamic flowering response to photoperiod. Lisson et al. (2000) investigated the critical daylength period for two European hemp varieties in a controlled environment, reporting a daylength-dependent photoperiod-induced phase. ...
... Lisson et al. (2000) investigated the critical daylength period for two European hemp varieties in a controlled environment, reporting a daylength-dependent photoperiod-induced phase. Some studies reported that shorter photoperiods induce early flowering (Amaducci et al., 2008b;Hall et al., 2012). Other authors have also found that longer photoperiods increased stem yield (Hall et al., 2014b;van der Werf et al., 1994) and production of cannabinoids (Valle et al., 1978). ...
... Understanding flowering pathways is critical to delineate growing seasons and determine suitable climatic regions for hemp varieties (Amaducci et al., 2015;Salentijn et al., 2019). The selection of inappropriate varieties can result in early flowering or a long flower development phase, producing low yields of the desired product and a heterogeneous crop that is mechanically impracticable to harvest (Amaducci et al., 2008b;Desanlis et al., 2013). ...
Article
Hemp (Cannabis sativa L.) has regained worldwide interest as a crop across temperate and subtropical regions. However, there is a paucity of information about the responses of hemp to environmental conditions and interactions between genotype and environment. This study compared the growth responses of a temperate hemp variety (Morphet Late) and three tropical/subtropical varieties (ECO-GH15, ECO-MC16 and ECO-YP16) to tropical daylengths (11.5 h and 12.5 h), temperatures and varying nitrogen (0, 50, 100, 150 kg ha⁻¹ of N) rates. Three experiments under controlled environmental conditions were conducted to test the growth, and cannabinoid production responses to N. Analysis of phenological data revealed significantly different responses between varieties in terms of days to emergence, time to flowering, growth patterns and final biomass showing predominant responses to daylength or temperature depending on the variety. Two tropical/subtropical varieties (ECO-GH15, ECO-MC16) responded similarly under all conditions; the other (ECO-YP16) showed a marked response to temperature rather than daylength, although all varieties had a strong biomass response to N increase. For all varieties, except the temperate variety, the concentration of Δ⁹-tetrahydrocannabinol (THC), cannabidiol (CBD), and some minor cannabinoids were significantly increased by a one-hour daylength increase. This study highlights the importance of temperature, daylength, and nitrogen for growth, time to flowering, and cannabinoid concentrations of different hemp varieties grown under tropical conditions and shows the importance of selecting low THC varieties for production in tropical/subtropical environments.
... Ce réseau complexe se décline selon les cultures considérées. Le lien entre la floraison et la qualité de la fibre est de plus en plus étudié sur la culture du chanvre (Amaducci et al., 2008;Petit et al., 2020), elle semble être un bon modèle pour la stévia. De façon identique à la stévia, le chanvre est sensible à la photopériode et sa floraison est inhibée par de longues photopériodes, la floraison est également utilisée comme point de référence pour la récolte (Salentijn et al., 2019). ...
... De façon identique à la stévia, le chanvre est sensible à la photopériode et sa floraison est inhibée par de longues photopériodes, la floraison est également utilisée comme point de référence pour la récolte (Salentijn et al., 2019). Le chanvre présente également une grande variabilité sur ce trait comme observé au sein du matériel génétique, en particulier sur la précocité de la floraison ainsi que la durée de cette même floraison (Amaducci et al., 2008). L'équipe d' Amaducci et al., (2012) a développé un modèle de prédiction de la date de floraison du chanvre en utilisant des données météorologiques et des paramètres phénologiques connus sur des cultivars. ...
Thesis
Le rejet des édulcorants de synthèse par les consommateurs a conduit ces derniers à privilégier les édulcorants naturels comme les glycosides de stéviol (SG). Ces molécules sont accumulées dans les feuilles de Stevia rebaudiana Bertoni, plante pérenne originaire du Paraguay, et aujourd’hui cultivée sur tous les continents. Dans le Sud-Ouest de la France, une filière de production en Agriculture Biologique est en développement, sous l’impulsion de la société Oviatis. Ce travail de thèse sous contrat CIFRE s’intéresse à la caractérisation fine des ressources génétiques cultivées sur les traits d’intérêt, et au développement des connaissances et des outils génétiques sur cette culture. La performance agronomique de la stévia a été évaluée par l’étude des composantes du rendement en SG, de l’architecture de la canopée et de la réponse à un agent fongique. Ces travaux ont permis (1) l’adaptation de l’échelle de stades phénologiques BBCH à la culture de la stévia et sa transmission à la filière, (2) l’évaluation des traits du rendement en SG sur 15 ressources génétiques de Stevia rebaudiana phénotypées pendant quatre années sur une parcelle expérimentale, (3) l’évaluation de la variabilité de la réponse à une infection de septoriose de ces mêmes ressources génétiques en conditions contrôlées et le développement d’un test d’inoculation sur disques foliaires, (4) d’estimer les paramètres génétiques pour les traits du rendement sur quatre populations de stévia cultivées en plein champ pendant trois ans, (5) enfin de construire des idéotypes de stévia dans le contexte local de production. Ces résultats participent au développement de la stévia dans le Sud-Ouest de la France, et alimentent la mise en place d’un programme d’amélioration pour une production en Agriculture Biologique.
... Cannabis sativa (Cannabaceae, Eudicot, Angiosperm) plants are generally dioecious (and rarely monoecious) and thus possesses unisexual flowers that are wind pollinated (Amaducci, Coluzzi, Zatta, & Venturi, 2008). Cannabis plants produce achenes that are have very thin perianths (Small E. , 2015). ...
Thesis
Full-text available
Cannabis sativa L. has been domesticated for fibre, oilseed, and marijuana; it also occurs as ruderal plants. "Marijuana" refers to plants selected for high concentrations of the chemical tetrahydrocannabinol (THC), while "hemp" refers to plants low in concentration of THC and which are domesticated for either stem fibre or oilseed. In my first chapter I review the botany of cannabis, taxonomy and origins, ethnobotany, and crop ferality. In my second chapter, I performed a study where achenes ("seeds") from herbarium collections representative of these classes of C. sativa were assessed for variation in morphological characters and pericarp resistance to fracture. Multivariate analysis of the data revealed significant divergence among the groups. In contrast to ruderal plants, domesticated plants (hemp or marijuana) possessed achenes that are significantly longer, heavier, covered with a less adherent perianth, and lacking a pronounced basal attenuation. These characteristics reflect traits that are advantageous in domesticated plants, and are consistent with the "domestication syndrome". Marijuana achenes, in comparison with hemp achenes, are shorter and darker. Achenes of fibre cultivars are larger than the achenes of oilseed cultivars. Achenes of dioecious oilseed cultivars are larger than the achenes of monoecious oilseed cultivars. We propose several mechanisms by which this phenotypic divergence may have occurred, including potential differences in outcrossing rate and the evolution of life history strategies among C. sativa groups that deserve further exploration. While only one species of Cannabis merits recognition, we postulate these phenotypic differences in C. sativa are a result of domestication for different purposes. In my final chapter I discuss the limitations and future studies. This work contributes a more complete understanding of cannabis morphology to the greater body of literature on plant domestication.
... Cannabis can grow under a variety of agroecological conditions [19], requires low input of water and fertilizers [20], and its cultivation becomes possible without the use of agrochemicals to control weeds, pests, and diseases [2]. This culture has a positive impact on the environment [21] and is an excellent cover crop that, thanks to its extensive root system, can improve soil structure [22] and its ability to adapt to different situations of abiotic stress [23]. In addition, there is growing interest in cultivating cannabis for other purposes, such as using its inflorescences to extract essential oils (EO) [24,25]. ...
Article
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A field experiment was carried out in Lebanon to assess the agronomic and essential oil characteristics of cannabis as affected by sowing date and irrigation practice. The experiment consisted of a split-plot design with the water regime being the main factor (Iopt-irrigated when the readily available soil water is depleted; I50-receiving 50% of the irrigation amounts in Iopt treatments) and sowing date as the sub-plot factor (mid-April; end of April; mid-May). Biometric and seed quality parameters of the cannabis crop were determined. The essential oils (EO) of the inflorescence were subjected to a multivariate analysis such as principal component analysis (PCA) and hierarchical cluster analysis (HCA). The obtained results revealed that the aboveground fresh biomass, the dry matter, and the plant height were 55.08%, 59.62%, and 43.11% higher in Iopt than in I50, respectively. However, the EO content was neither statistically affected by the irrigation regime nor by the sowing date. Under early sowing, both the water-use efficiency (WUE) for biomass and the EO production reached their highest values. All treatments presented a similar seed composition except that the crude fat and crude protein content were more elevated in Iopt than in I50 treatments. The main extracted essential oils in cannabis inflorescence corresponded to twenty-six identified compounds representing 79.34% of the monoterpenes and 81.25% of the sesquiterpenes. The mon-oterpenes were highly correlated with the irrigation treatment and early-April sowing while the sesquiterpenes were better enhanced under I50 and end of April to mid-May sowing. The study reveals that agronomic practices lead to differential responses of pharmacologically useful plant compounds for improved health benefits. Further research is required to clarify the potential for cannabis cultivation in Lebanon.
... Growers sow later in the season to avoid early season weed competition and to control final plant height at harvest (personal communication). Hemp is a quantitative short-day plant for flowering and plant growth is considerably reduced following flower initiation [24]. ...
Article
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Industrial hemp (Cannabis sativa L.) as a grain and fiber crop is experiencing a resurgence in North America. Due to governmental prohibition, there has been limited information on regional agronomic production systems including basic information on seed germination. This study was initiated to provide basic information on the relationship between temperature and germination in hemp seed. Germination was measured at constant temperatures ranging from 3 to 42 °C. Cardinal temperatures were determined for two industrial oil crop hemp cultivars (‘Georgina’ and ‘Victoria’). The optimal germination temperature indicated by a high mean germination percentage and rate was between 19 and 30 °C. Optimal (29.6 °C), base (3.4 °C) and ceiling (42.6 °C) temperatures were calculated from a linear regression of the germination rates to reach 50% germination for each temperature. The thermal time for ‘Georgina’ and ‘Victoria’ to reach 50% germination at suboptimal temperatures was 694 and 714 °C h, respectively. The osmotic and solid matrix-primed hemp seeds germinated faster than the untreated seeds, but the final germination percentages were not different. The primed seeds germinated faster at supraoptimal temperatures but did not impact final germination percentages in the thermally inhibited seeds.
... Flowering in plants is a physiological phenomenon that is influenced by endogenous plant growth regulators, vernalization, photoperiod, and several other yet-to-be identified factors [23]. Days to flowering is an important factor to cultivar selection as similar flowering times within a variety indicates potential uniformity of the crop in the field [24]. Furthermore, days to flowering is especially a vital factor in industrial hemp as its unique secondary metabolites are produced in the flowers. ...
Preprint
Industrial activities have a detrimental impact on the environment and health when high concentrations of pollutants are released. Phytoremediation is a natural method of utilizing plants to remove contaminants from the soil. The goal of this study was to investigate the ability ofCannabis sativaL. to sustainably grow and remediate abandoned coal mine land soils in Pennsylvania. In this study, six different varieties of industrial hemp (Fedora 17, Felina 32, Ferimon, Futura 75, Santhica 27, and USO 31) were grown on two different contaminated soil types and two commercial soils (Miracle-Gro Potting Mix and PRO-MIX HP Mycorrhizae High Porosity Grower Mix). Plants growing in all soil types were exposed to two environmental conditions (outside and in the greenhouse). Seed germination response and plant height indicated no significant differences among all hemp varieties grown in different soils, however on an average, the height of the plants grown in the greenhouse exceeded that of the plants grown outdoors. In addition, heavy metal analysis of Arsenic, Lead, Nickel, Mercury, and Cadmium was performed. The concentration of Nickel was 2.54 times greaterin the leaves of hemp grown in mine land soil outdoors when compared to greenhouse conditions. No differences were found between expression of heavy metal transporter genes. Secondary metabolite analysis of floral buds from hemp grown in mine land soil displayed a significant increase in the total Cannabidiol content (2.16%, 2.58%) when compared to Miracle-Gro control soil (1.08%, 1.6%) for outdoors and in the greenhouse, respectively. Molecular analysis using qRT-PCR indicated an 18-fold increase in the expression of the cannabidiolic acid synthasegene in plants grown on mine land soil.Thedata indicates a high tolerance to heavy metals as indicated from the physiological and metabolites analysis.
... Cannabis is extremely influenced by photoperiod and temperature, the short-day condition with uninterrupted darkness of ∼10-12 h is given which induces the flowering instantaneously (Amaducci et al. 2008a;Salentijn et al. 2019)). However, cannabis cultivated in 24 h light also flowered, but dry matter content in the floral parts are largely reduced (Schaffner 1926). ...
Chapter
Cannabis is the most versatile species. Hemp and marijuana have been used for fibre, oil, medicinal and recreational purposes from millennia. Throughout the last century, the plant has been generally outlawed because of its psychotropic effects in many nations. In recent past, the studies on cannabis revealed the evidence of its high medicinal properties and its uses in treating life threatening diseases, which leads to the relaxation of legislation in many counties. Now, the genetic and genomics as well as the cannabis derived products enjoys renewed attention. In this chapter, the discussion was made on the advent of genomics and breeding strategies to improve various traits of cannabis. This will bring insights on future direction of cannabis breeding.
Chapter
Nowadays, the light hemp is promoted by different stakeholders and the customer’s preference due to the different use of crop products. The aim of this chapter was to discuss the Italian perspectives concerning the utilization of light hemp connected to customer’s preferences. It is discussed the sustainability of hemp crop to produce wellness products in Italy. It is applied as a cost model based on empirical data from hemp farmers. Customers’ preferences on light cannabis wellness products are analyzed through an online survey in Italy and other six European countries. A general misunderstanding about the differences between psychoactive hemp and nonpsychoactive hemp (light cannabis) makes the demand unstable. Light hemp business in Italy is new and there are a few studies that help entrepreneurs in assessing the attractiveness of certain investment analyzing the demand for such a product. Demand for CBD-based products indicates interest, but customers’ confusion highlights a lack of regulation and transparency about CBD-cannabis.
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The European Community co-financed Project HEMP SYS aims at researching and developing an entire production chain for hemp based textiles, starting with the cultivation of the crop and finishing with the end-products. The innovative production chain herewith developed is based on green decortication of the hemp stems cut into 1 m long sections, and subsequent industrial microbiological retting of the scutched fiber. Considering the industrial demand for a consistent quantity of fiber of homogeneous quality, how quality is affected by a variation in the production factors along the production system is studied. Field trials are carried out at multiple locations to determine the effect of Genotype x Environment x Management on hemp production. Different harvesting techniques, mechanical fiber separation methods, fiber preparation for further treatment are all evaluated. Fiber retting and fiber cleaning are carried out on a pilot plant set up in the framework of a regional research programme (www.toscanapa.it). Fiber samples are collected at different stages of transformation and are analyzed for quality characteristics. In this presentation, preliminary results from a selected combination of experiments will be presented and discussed. Stem and fiber production increased with harvest time, but fiber-bundle finesses tended to be higher for the early harvest times (beginning of flowering). Plant density affected stem and fiber production in only a few cases, while fiber-bundle fineness tended to increase at higher densities. Fineness of single fiber was also measured in portions of stem taken at different plant height in order to evaluate interplant variability of fiber quality. It was noted that the average fineness of the primary fiber tends to be higher in the lower and central portions of the stem. The practical implications of these results are discussed, highlighting the strategies of quality control developed within the production chain proposed in the Hemp Sys Project.
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. Hemp (Cannabis sativa L.) fibre can be used as a raw material for paper and textile production. A comprehensive research programme in the Netherlands has concluded that fibre hemp is a potentially profitable crop, having the right profile to fit into sustainable farming systems. This paper presents an appraisal of the crop physiological characteristics and the agronomic potential of hemp. Parameter values of basic crop physiological characteristics such as light interception potential, radiation use efficiency and dry matter partitioning coefficients are given. The effect of crop management decisions such as cultivar choice, sowing date, plant density, and harvest date on the value of these parameters is discussed. A simple crop growth model was used to assess the yield potential of hemp for the climate of the Netherlands. Calculations made for a non-stressed late-flowering hemp crop sown on 15 April and harvested on 15 September give a stem dry matter yield of 17.1 t ha-1. The effects of advancing or delaying sowing or harvest date on stem yield were calculated. Crop physiological characteristics of hemp are compared to those of kenaf (Hibiscus cannabinus L.). Radiation use efficiency and dry matter partitioning coefficients of the two crops are similar. Base temperatures for development and growth are lower in hemp than in kenaf. In a temperate climate with cool springs, canopy establishment will be more rapid in hemp than in kenaf. Hemp seems an excellent candidate to fill the niche for an annual fibre crop in a temperate climate.
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Research and development of an innovative production system for hemp (Cannabis sativa L.) fibre for textile use requires the integration of multidisciplinary knowledge from cultivation technique to realization of end products. Research was carried out to study the effect of the agronomic factors cultivation year (2003–2004), genotype (Futura 75 and Tiborszallasi), plant population (120, 240 and 360plantsm−2) and harvesting time (beginning and full flowering) on fibre yield and quality in the whole hemp stem, and in the basal and apical stem portions separately. The study of separate stem portions was done to determine the effect on fibre quality of an innovative harvesting and processing system in which hemp stems are cut in two portions of approximately 1m at harvest to enable processing on modern flax scutching lines.Stem and fibre yield were affected by most of the agronomic factors. The extreme drought experienced in the first year reduced stem and fibre yield, but stems had higher percentage of fibre (16.5%), that were finer (22.9μm) and with a higher degree of maturity (73.6%) in 2003 than in 2004 (respectively 16.0%; 24.5μm; 55.8%). Between the two genotypes under trial the monoecious Futura 75 largely out yielded the dioecious Tiborszallasi in both years. The latter however had finer primary fibres and less secondary ones. In both genotypes primary fibres maturity and quantity of secondary fibres increased at later harvest.Plant population affected stem biometrics and fibre characteristics, with finer fibres and less secondary growth at higher stands.It can be concluded that cultivation technique can be exploited in order to maximize the quality and yield of stems destined for the innovative harvesting and processing system herein described.
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This paper reports on a 4-year study into the effect of plant density on the morphology and production of fibre hemp. At high density (180-270 plants m), strong competition for light early in the growing season promoted internode extension (primary growth) and inhibited increase of stem diameter (secondary growth). In relating plant density to fibre hemp production it can therefore be said that a high plant population favours a high yield of long bast fibres for the textile industry. Demands only for high total yield can however be satisfied by targeting 30-45 plants mr. This is further supported by results of self-thinning, showing plant loss in 1999 was negligible at low density (30-90 plants m), while at high density (180 and 270 plants m) 50% and 60% of the initial stand was lost, respectively. In view of this result, and because of the fact that no significant morphological difference was found between 180 and 270 plants m, it is also worth to note that when growing for long bast fibres 180 plants m should be chosen instead of 270 in order to save seed costs.
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The feasibility of utilizing kenaf (Hibiscus cannabinus L.) as a fibre crop and potential source of paper pulp is being investigated. This paper is the first in a series which develops and validates a simulation model of kenaf, and applies it to assessing the potential for dryland production in regions of tropical Australia. The duration from sowing to flowering is an important determinant of fibre yield in kenaf. Accordingly, the effect of temperature and photoperiod on the phenology of kenaf was examined. Data were collated from sowing-date experiments on kenaf cultivars Guatemala 4 and Everglades 71 at six locations in tropical Australia, ranging in latitude from 12-degrees-54'S. to 19-degrees-32'S. Data from one site, Kununurra, W.A. (15-degrees-39'S.), was used to develop a model which described the duration from sowing to flowering in kenaf based on four stages: (1) sowing to emergence; (2) emergence to the end of the basic vegetative phase (BVP); (3) a photoperiod-induced phase (PIP) which ends at floral initiation, and (4) a flower development phase (FDP). Both kenaf cultivars responded as qualitative short-day plants where flowering did not occur above a critical photoperiod of 12.9 h. Assuming a base photoperiod of 12.0 h, the thermal time required to complete the BVP for the two cultivars was similar. However, photoperiod sensitivity during PIP, and the thermal time required for FDP, were greater for Guatemala 4 than for Everglades 71. Validation of the model against independently observed data for both cultivars at other sites resulted in close predictions in the thermal time required for flowering. This phenological model for kenaf can be used to assess the effect of sowing date on phenology at different locations in tropical environments, and is a key component of a crop growth simulation model to assess the environmental constraints to productivity in these regions.
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The duration from sowing to flowering is an important determinant of fibre yield potential in hemp, since maximum stem yield occurs shortly after flowering. As a short-day plant, daylength has a key influence on the timing of flowering in hemp. This paper reports on studies into the effect of photoperiod on the thermal time duration from sowing to flowering for 2 hemp cultivars, and develops parameters to enable simulation of post-emergent phenology in the hemp model described in the final paper of this series. The hemp model divides the post-emergent period into a vegetative phase that ends at floral initiation, aflower development phase (FDP) between flower initiation and appearance, and a short phase between first flower appearance and harvest maturity (male anthesis). The vegetative phase is further divided into a temperature-dependent basic vegetative phase (BVP) and a daylength-dependent photoperiod induced phase (PIP). For a short-day plant, the duration of PIP is assumed to be zero degree days at daylengths below a base or maximum optimum photoperiod (MOP). Daylengths in excess of the MOP lead to an increase in thermal time within PIP, the duration of which is determined by a genotype’s photoperiod sensitivity (PS). Two hemp genotypes, Kompolti and Futura 77, were exposed to 6 different photoperiod regimes ranging from 8 to 16 h in a growth chamber. Thermal time durations from emergence to flower initiation and first flower formation (harvest) were calculated from thermograph plots. The flowering responses for the 2 cultivars were typical for a short-day plant, with flowering occurring rapidly in daylengths less than about 14 h and with increasing delay at longer photoperiods. With the exception of a longer thermal time duration from flower formation to harvest maturity in the case of Kompolti, the 2 cultivars had similar values for the key phenology parameters. Respectively, for Futura and Kompolti: BVP was 383˚Cd and 390˚Cd, MOP was 14 h and 13.8 h, PS was 266˚Cd/h and 252˚Cd/h, and FDP was 76.8˚Cd and 80.2˚Cd.
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The S-shaped logistic growth model has been extensively studied and applied to a wide range of biological and socio-technical systems. A model, the Bi-logistic, is presented for the analysis of systems that experience two phases of logistic growth, either overlapping or sequentially. A nonlinear least-squares algorithm is described that provides Bi-logistic parameter estimates from time-series growth data. Model sensitivity and robustness are discussed in relation to error structure in the data. A taxonomy and some examples of systems that exhibit Bi-logistic growth are presented. The Bi-logistic model is shown to be superior to the simple logistic model for representing many growth processes.
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The variation of Cannabis in phenological development and in stem elongation was studied in relation to stem production. In two field evaluations, one including 98 and the other 75 accessions, large variation was found for day of anthesis and day of seed maturity. A higher latitude of origin of accessions was associated with earlier anthesis and seed maturity. The phenological pattern proved to be stable over years.Stem elongation in the evaluation trial of 98 accessions was characterized by the slope coefficient, inflexion point, and upper asymptote of a sigmoid curve fitted to periodical measurements of stem length. Significant differences among accessions were found for each of these curve parameters. Stem elongation was less stable than the phenological pattern over years. The stem elongation parameters were significantly correlated with the day numbers of anthesis and seed maturity. Early-flowering accessions were shorter than late ones. The influence of phenological development on stem elongation was however only evident for relatively early-flowering accessions. Stem elongation of Cannabis continued generally after the onset of anthesis. The proportion of the stem formed in the generative stage was larger the earlier accessions started to flower. Very late-flowering accessions reached the ultimate length in the vegetative stage.In the evaluation trial consisting of 75 accessions, phenological development and final stem length were observed in relation to stem dry matter production. Day of anthesis and final stem length were strongly and positively related with stem yield. Some very late-flowering landraces of fibre hemp exceeded by far the standard fibre cultivars in stem yield. Late-flowering drug strains were less persistent than late fibre strains in a dense crop situation.It was concluded that in an efficient crop growth system, seed production and stem production should occur in separate geographic areas, i.e. seed production at lower latitude and stem production at higher latitude. Breeding can contribute to yield potential by improving the persistency of cultivars. There seem also possibilities to select for more efficient stem dry matter accumulation and dry matter partitioning.
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Traditionally, hemp is a plant very well suited to Italian pedo-climatic conditions. The textile fibre produced in the past was of the finest quality due to integrated selected local varieties, good agrotechnology and experienced retting techniques. Attempts to reintro-duce this crop in Italy rely upon updating the chain of fibre production and its processing that lead to the textile and its derivatives. This article discusses a new research project designed to study production and utilization of the plant.