Duration Of Vernalization Research Articles

Reducing the generation time in winter wheat cultivars using speed breeding

AbstractReducing generation time is critical to achieving the goals of genetic gain in important crops like wheat (Triticum aestivum). Speed breeding (SB) has been shown to considerably reduce generation times in crop plants. Unlike spring wheat cultivars, winter wheat varieties require typically 6–9 weeks of cold treatment, called vernalization, for flowering which extends the generation time for the development of improved winter wheat cultivars. Here, we optimized the SB method using a set of 48 diverse soft red winter wheat (SRWW) cultivars by testing vernalization duration, light and temperature requirements, and the viability of seeds harvested after different durations post‐anthesis under extended daylight conditions. We have found that using a 22‐h setting (22 h day/2 h night, 25°C/22°C) in high‐density 50‐cell trays results in rapid generation advancement. We used genotypic data for a panel of soft red winter wheat varieties from the regional programs to determine the impact of photoperiod and vernalization alleles on the efficiency of the SB approach. Using a set of 48 SRWW cultivars and germplasm from Maryland and four other public breeding programs, we establish that this protocol can allow for the advancement of four generations per year in controlled conditions for winter wheat varieties, experimental lines, or emerging cultivars. Our work shows the potential to reduce generation time by ∼30 days per generation faster than what had been reported in the SB strategies for winter wheat, thus allowing for a quicker turnaround time from original cross to genetically stable experimental genotypes that can be tested in field settings.

Temperature and duration of vernalization effect on the vegetative growth of garlic (Allium sativum L.) clones in Indonesia

Abstract Garlic is usually propagated asexually from the cloves. Clove as the propagation source for garlic has many weaknesses. Alternatively, bulbils could be used for the propagation. The aim of this study was to know the effect of temperature and time of vernalization from several clones of Indonesian garlic to bulbil production. This research was conducted at a farmer’s field at Banjarnegara, Central Java, Indonesia. The experiment was arranged in a Completely Randomized Block Design with three factors: temperature of vernalization, i.e., 0, 5, and 10°C, duration of vernalization, i.e., 20, 40, and 60 days, and on 12 garlic varieties/clones (V1–V12). Cloves of garlic were vernalized in cold storage according to the treatments and then planted in the field. The results revealed that a temperature of 5°C and duration of 20 days of vernalization independently single factor increased the number of bulbils of V3. Bulbil variables of V4 and V7 were enhanced with vernalization at 0°C for 20 days, although it did not significantly differ from the control. Therefore, these clones do not need particular vernalization treatment in order to produce bulbils.

Depicting Precise Temperature and Duration of Vernalization and Inhibiting Early Bolting and Flowering of Angelica sinensis by Freezing Storage.

Angelica sinensis is a perennial rhizomatous herb that is widely used for the treatment of cardio-cerebrovascular diseases, which largely rely on metabolites, such as alkylphthalides, polysaccharides, and ferulic acid. This plant must experience low-temperature vernalization and long-day conditions for the occurrence of early bolting and flowering (EBF) that reduces yield and quality of fleshy root. In current commercial planting, the EBF of more than 40% is mainly attributed to the completion of vernalization of seedlings during overwinter storage. While effects of storage temperatures [vernalization temperature (0–10°C) and freezing temperature (−2 to −12°C)] and seedling sizes on the EBF have been observed in previous studies, the precise vernalization temperature and duration for different size seedlings, the effective freezing storage to avoid vernalization of seedlings, and physiological characteristics have not been systematically investigated. Here, the EBF rate, the anatomical structure of shoot apical meristem (SAM), and physiological characteristics of different size seedlings at different storage temperatures (0, 3, 5, −3, and −5°C) and durations (14–125 d) are reported. The vernalization duration of seedlings was predicated from 57 to 85 d with temperatures ranging from 0 to 5°C based on the linearization regression analysis via Matrix Laboratory software. The EBF can be effectively inhibited by freezing storage. The anatomical structure of SAM, levels of primary metabolites (soluble sugar, starch, amino acid, and protein), and endogenous hormones (GA3, IAA, and ABA), exhibited a dynamical change in the seedlings at different storage temperatures. These findings will provide useful information for predicting the vernalization of seedlings and inhibiting the EBF in large-scale commercial cultivation.

The need for the vernalization duration of soft winter wheat collection samples

The need for vernalization is a duration-dependent effect of low, positive temperatures in order to ensure the plants' transition to generative development. If the requirement for the duration of germination is not met, the plant will not enter the stage of forming generative organs. The vernalization requirements of winter soft wheat samples of different geographical origins are determined. An assessment of the vernalization period duration influence on the severity of the elements of the yield structure is given. The research material consisted of 15 cultivars of soft winter wheat of various geographic origin. The samples were germinated in paper rolls, then vernalized in a climatic chamber at a temperature of 3–5 ºС for 60, 50, and 40 days. At the end of vernalization, 10 plants of each sample were planted in a greenhouse. The dates of the onset of phenological phases were noted: tube emergence, earing, flowering. To determine the main elements of the yield structure, a structural analysis of plants was carried out. With an increase in the vernalization period, a decrease in the interfacial periods from tube emergence to flowering was noted. The influence of the timing of vernalization was noted on the manifestation of the spike length trait. It was found that the total number of stems and the number of productive stems in almost all varieties decreases with an increase in the period of vernalization. Significant differences between collection varieties in the need for vernalization, due to both their geographical origin and the genotype of plants are revealed. In all the studied forms, with an increase in the period of vernalization, the rate of plant development increased to varying degrees, the total number of stems, the productive stem and the length of the spike decreased.

Features of transcriptional dynamics of the duplicated Vernalization‐B1 gene in wheat (Triticum spp.)

AbstractThe Vernalization‐1 genes are the key determinants of the vernalization requirement of wheat. In the present study, for the first time, the characteristics of VRN‐B1 expression were investigated in accessions of winter hexaploid wheat of Triticum spelta, carrying one and two copies of this gene per haploid genome. Expression of duplicated VRN‐B1 was analysed relative to the single copy allele during vernalization and following vegetative growth. Furthermore, the effect of vernalization duration on transcriptional activity of the duplicated VRN‐B1 was evaluated. The results obtained assume prolonged activation of the recessive vrn‐B1 alleles with an increase in their copies in the genome. One of the noted features of VRN‐B1 expression was unpredictable and unexpected sharp decrease in expression of duplicated VRN‐B1, compared with the single haploid copy of this gene, after incomplete vernalization. This is an important new finding in transcriptional dynamics of the recessive vrn1 alleles with increased copy number, which expands our knowledge about the vernalization response of wheat and provides a new tool in the manipulation of agronomically valuable traits during wheat breeding.

Variation in seasonal timing traits and life history along a latitudinal transect in Mimulus ringens.

Seasonal timing traits are commonly under recurrent, spatially variable selection, and are therefore predicted to exhibit clinal variation. Temperate perennial plants often require vernalization to prompt growth and reproduction; however, little is known about whether vernalization requirements change across the range of a broadly distributed species. We performed a critical vernalization duration study in Mimulus ringens, coupled with population genomic analysis. Plants from eight populations spanning the latitudinal range were exposed to varying durations of 4°C vernalization between 0 and 56days, and flowering response was assessed. RADSeq was also performed to generate 1179 polymorphic SNPs, which were used to examine population structure. We found unexpected life history variation, with some populations lacking vernalization requirement. Population genomic analyses show that these life history variants are highly divergent from perennials, potentially revealing a cryptic species. For perennial populations, minimum vernalization time was surprisingly consistent. However, once vernalized, northern populations flowered almost 3weeks faster than southern. Furthermore, southern populations exhibited sensitivity to vernalization times beyond flowering competency, suggesting an ability to respond adaptively to different lengths of winter. Mimulus ringens, therefore, reveals evidence of clinal variation, and provides opportunities for future studies addressing mechanistic and ecological hypotheses both within and between incipient species.

Transposition and duplication of MADS-domain transcription factor genes in annual and perennial Arabis species modulates flowering

The timing of reproduction is an adaptive trait in many organisms. In plants, the timing, duration, and intensity of flowering differ between annual and perennial species. To identify interspecies variation in these traits, we studied introgression lines derived from hybridization of annual and perennial species, Arabis montbretiana and Arabis alpina, respectively. Recombination mapping identified two tandem A. montbretiana genes encoding MADS-domain transcription factors that confer extreme late flowering on A. alpina These genes are related to the MADS AFFECTING FLOWERING (MAF) cluster of floral repressors of other Brassicaceae species and were named A. montbretiana (Am) MAF-RELATED (MAR) genes. AmMAR1 but not AmMAR2 prevented floral induction at the shoot apex of A. alpina, strongly enhancing the effect of the MAF cluster, and MAR1 is absent from the genomes of all A. alpina accessions analyzed. Exposure of plants to cold (vernalization) represses AmMAR1 transcription and overcomes its inhibition of flowering. Assembly of the tandem arrays of MAR and MAF genes of six A. alpina accessions and three related species using PacBio long-sequence reads demonstrated that the MARs arose within the Arabis genus by interchromosomal transposition of a MAF1-like gene followed by tandem duplication. Time-resolved comparative RNA-sequencing (RNA-seq) suggested that AmMAR1 may be retained in A. montbretiana to enhance the effect of the AmMAF cluster and extend the duration of vernalization required for flowering. Our results demonstrate that MAF genes transposed independently in different Brassicaceae lineages and suggest that they were retained to modulate adaptive flowering responses that differ even among closely related species.

The influence of the hybrid and the duration of vernalization of tuberous roots on photosynthesis and flowering in Ranunculus asiaticus L.

The influence of the hybrid and the duration of vernalization of tuberous roots on photosynthesis and flowering in <i>Ranunculus asiaticus</i> L.

Effect of different vernalization duration on seed yield in white head cabbage

Effect of different vernalization duration on seed yield in white head cabbage

Extended Vernalization Regulates Inflorescence Fate in Arabis alpina by Stably Silencing PERPETUAL FLOWERING1.

The alpine perennial Arabis alpina initiates flower buds during prolonged exposure to cold. In the accession Pajares, we demonstrate that the length of vernalization influences flowering time and inflorescence fate but does not affect the axillary branches that maintain vegetative growth. The expression of floral organ identity genes gradually increases in the main shoot apex during vernalization, correlating with an increase in floral commitment. In northern Arabidopsis (Arabidopsis thaliana) accessions, the length of vernalization modulates the stable silencing of the floral repressor FLOWERING LOCUS C (FLC). We demonstrate that expression of PERPETUAL FLOWERING1 (PEP1), the ortholog of FLC in A. alpina, is similarly influenced by the duration of the exposure to cold. Extended vernalization results in stable silencing of PEP1 in the inflorescence. In contrast, insufficient vernalization leads to PEP1 reactivation after cold treatment, which correlates with delayed flowering and the appearance of floral reversion phenotypes such as bracts and vegetative inflorescence branches. Floral reversion phenotypes are reduced in the pep1-1 mutant, suggesting that PEP1 regulates the fate of the inflorescence after vernalization. The effect of vernalization duration on stable silencing of PEP1 is specific to meristems that initiate flowering during cold treatment. Extended vernalization fails to silence PEP1 in young seedlings and axillary branches that arise from buds initiated during cold treatment, which remain vegetative. We conclude that the duration of vernalization in A. alpina differentially regulates PEP1 in the inflorescence and axillary branches. PEP1 has a dual role regulating meristem fate; it prevents meristems from flowering and antagonizes inflorescence development after vernalization.

The relationship among freezing tolerance, vernalization requirement, Ppd alleles and winter hardiness in European wheat cultivars

SUMMARYWinter hardiness of wheat is a complex trait involving a system of structural, regulatory and developmental genes, which interact in a complex pathway. The objective of the present work was to study the relationship among the main traits determining the level of adaptation and the possibility for target manipulation of breeding material by using molecular markers and phenological parameters. Wheat cultivars from different ecoclimatic environments of Europe were included for analysis. Gene-specific assay showed that photoperiod sensitivity of the studied cultivars was determined by polymorphism in the Ppd-D1 allele. The study established the relationship among winter hardiness, LT50 (the temperature at which 50% of plants are killed), photoperiod sensitivity, vernalization duration and earliness per se genes in the environment of Lithuania. The cultivars from Northern and Western Europe exhibited stronger requirement for vernalization and photoperiod. Although the group of cultivars from the southern latitudes were characterized by earliness, they possessed a stronger level of LT50. The level of LT50 was found to be the most crucial component of winter hardiness, the other traits served as supplementary components.

Cell Wall Composition and Biomass Recalcitrance Differences Within a Genotypically Diverse Set of Brachypodium distachyon Inbred Lines.

Brachypodium distachyon (Brachypodium) has emerged as a useful model system for studying traits unique to graminaceous species including bioenergy crop grasses owing to its amenability to laboratory experimentation and the availability of extensive genetic and germplasm resources. Considerable natural variation has been uncovered for a variety of traits including flowering time, vernalization responsiveness, and above-ground growth characteristics. However, cell wall composition differences remain underexplored. Therefore, we assessed cell wall-related traits relevant to biomass conversion to biofuels in seven Brachypodium inbred lines that were chosen based on their high level of genotypic diversity as well as available genome sequences and recombinant inbred line (RIL) populations. Senesced stems plus leaf sheaths from these lines exhibited significant differences in acetyl bromide soluble lignin (ABSL), cell wall polysaccharide-derived sugars, hydroxycinnamates content, and syringyl:guaiacyl:p-hydroxyphenyl (S:G:H) lignin ratios. Free glucose, sucrose, and starch content also differed significantly in senesced stems, as did the amounts of sugars released from cell wall polysaccharides (digestibility) upon exposure to a panel of thermochemical pretreatments followed by hydrolytic enzymatic digestion. Correlations were identified between inbred line lignin compositions and plant growth characteristics such as biomass accumulation and heading date (HD), and between amounts of cell wall polysaccharides and biomass digestibility. Finally, stem cell wall p-coumarate and ferulate contents and free-sugars content changed significantly with increased duration of vernalization for some inbred lines. Taken together, these results show that Brachypodium displays substantial phenotypic variation with respect to cell wall composition and biomass digestibility, with some compositional differences correlating with growth characteristics. Moreover, besides influencing HD and biomass accumulation, vernalization was found to affect cell wall composition and free sugars accumulation in some Brachypodium inbred lines, suggesting genetic differences in how vernalization affects carbon flux to polysaccharides. The availability of related RIL populations will allow for the genetic and molecular dissection of this natural variation, the knowledge of which may inform ways to genetically improve bioenergy crop grasses.

Vernalization Duration Requirement in Soft Winter Wheat is Associated with Variation at the VRN‐B1 Locus

ABSTRACTGenetic variation in the factors controlling flowering in wheat (Triticum aestivum L.) allow it to be grown in a wide range of environments. The aim of this study was to identify genetic determinants of flowering time in winter wheat cultivars adapted to regions of the United States differing in latitude and the duration of cold temperatures during winter. Quantitative trait locus (QTL) analysis was performed in a recombinant inbred line (RIL) population from the cross between cultivars NC‐Neuse and AGS 2000 that are adapted to the Mid‐Atlantic and Southeastern regions, respectively. We identified a QTL for heading date (HD) in the greenhouse after 4 wk of vernalization, designated Qvdr.nc‐5BL, which also had a large effect on winter dormancy release and HD when the population was evaluated in the field at locations in North Carolina, Georgia, and Louisiana during 2012 and North Carolina during 2013. However, Qvdr.nc‐5BL did not have a significant effect on HD in greenhouse grown plants vernalized for 8 wk or in plants grown in the field at Raleigh, NC during 2011. In those environments where Qvdr.nc‐5BL was not significant, a region on chromosome 2B, probably associated with the Ppd‐B1 locus, was determined to have a HD effect. Interrogation of the population with gene‐based markers for Vrn‐B1 and Ppd‐B1 suggests that these loci are major determinants of HD in winter wheat and are important for adaptation to diverse growing environments.

Development of new quantitative physiological and molecular breeding parameters based on the sugar-beet vernalization intensity model

SUMMARYSugar-beet crops, Beta vulgaris spp. vulgaris (L), suffer from premature bolting and flowering as a consequence of prolonged exposure to cold conditions (vernalization). This reduces crop yield and quality and could be avoided if bolting-resistant varieties were available. Traditionally, development of bolting-resistant varieties has relied on selection against the annual growth habit associated with the bolting gene B. However, this has failed to deliver crops that can be reliably sown in early spring or grown over winter without the risk of bolting. New breeding targets and selection strategies are required and have become tractable with the recent development of the vernalization-intensity model. This model uses parameters for the intensity and duration of vernalization (vernalization hours) to predict bolting responses and discriminates between varieties by the minimum number of vernalization hours needed to induce bolting (vernalization requirement (VR)) and by the increase in bolting incidence for each extra vernalizing hour once the VR has been satisfied (bolting sensitivity (BS)). Since the vernalization-intensity model was developed from variety-assessment trials data, the present work sought to refine and test it through controlled environment (CE) experiments in which seven sugar-beet varieties were exposed to differing levels of accurately defined vernalization treatments and scored for bolting rates to determine their VR and BS values. The results confirmed and improved the model and showed that VR, not BS, has more potential for developing bolting resistant varieties. It was also observed that there exist in current varieties, the genetic potential to breed for higher VR. Further experiments assessed the correlation of attainment of VR with changes in gene expression and shoot apical meristem (SAM) morphology to identify potential markers for this trait. It was found that the time when VR is attained correlates with up-regulation of gibberellin biosynthetic genes and floral transcription factors in leaf and shoot apices; most prominently, GIBBERELLIN 20-OXIDASE 2 (BvGA20ox2) and FLOWERING LOCUS T 2 (BvFT2). To integrate the results with weather data, temperature records for the past 47 years from the Broom's Barn weather station were used to develop a tool for predicting accumulated vernalization hours based on sowing date. The results, together with data from the CE experiments, were used to establish VR-breeding targets for bolting-resistant varieties for spring- and autumn-sown sugar-beet crops. The present paper shows that integration of weather, VR and genetic data provide useful tools to aid both cultivation and breeding selection. For growers, it provides a weather data tool to assist with the selection of suitable sowing dates. For breeders, it provides the first identification of molecular genetic factors that correlate with VR and the physiological changes associated with vernalization responses in sugar beet. The results suggest that gene-expression profiles can be developed into tools for quantifying bolting resistance in beet, thereby providing a cost-effective, high-throughput and simple method for breeders to apply the vernalization-intensity model.

AaTFL1Confers an Age-Dependent Response to Vernalization in PerennialArabis alpina

Flowering of many plants is induced by environmental signals, but these responses can depend on the age of the plant. Exposure of Arabidopsis thaliana to vernalization (winter temperatures) at germination induces flowering, whereas a close perennial relative Arabis alpina only responds if exposed when at least 5 weeks old. We show that vernalization of these older A. alpina plants reduces expression of the floral repressor PEP1 and activates the orthologs of the Arabidopsis flowering genes SOC1 (Aa SOC1) and LFY (Aa LFY). By contrast, when younger plants are vernalized, PEP1 and Aa SOC1 mRNA levels change as in older plants, but Aa LFY is not expressed. We demonstrate that A. alpina TFL1 (Aa TFL1) blocks flowering and prevents Aa LFY expression when young plants are exposed to vernalization. In addition, in older plants, Aa TFL1 increases the duration of vernalization required for Aa LFY expression and flowering. Aa TFL1 has similar functions in axillary shoots, thus ensuring that following a flowering episode vegetative branches are maintained to continue the perennial life cycle. We propose that Aa TFL1 blocks flowering of young plants exposed to vernalization by setting a threshold for a flowering pathway that is increased in activity as the shoot ages, thus contributing to several perennial traits.

Vernalization Duration and Light Intensity Influence Flowering of Three Hybrid Nobile Dendrobium Cultivars

The flowering time and flower quality of three hybrid Dendrobium nobile cultivars in relation to light intensity during cooling and duration of vernalization were studied in the first experiment. Mature Dendrobium Red Emperor ‘Prince’, Den. Sea Mary ‘Snow King’, and Den. Love Memory ‘Fizz’ plants were vernalized at 10 °C under 300 to 350 μmol·m−2·s−1 photosynthetic photon flux (PPF) (12-h photoperiod) or darkness, each with four cooling durations (2, 4, 6, or 8 weeks). Plants were forced in a greenhouse after vernalization. At least 4 weeks of 10 °C cooling in light was needed for complete flower initiation of Den. Red Emperor ‘Prince’, whereas Den. Sea Mary ‘Snow King’ and Den. Love Memory ‘Fizz’ only needed 2 weeks of 10 °C cooling regardless of light. For all three cultivars, darkness during vernalization slightly delayed flowering and resulted in fewer but larger flowers. Longer cooling duration delayed flowering, decreased flower longevity, and produced more and larger flowers. In a second experiment, Den. Love Memory ‘Fizz’ plants were vernalized at 15 °C for 4 weeks under a 12-h photoperiod and PPF of 0, 50, 100, or 200 μmol·m−2·s−1. Compared with 200 μmol·m−2·s−1, low PPF at 50 or 100 μmol·m−2·s−1 did not affect flowering time or flower qualities; however, darkness delayed flowering and reduced flower qualities except flower diameter.

Dianthus gratianopolitanus Vill. ‘Bath's Pink’ has a Near-obligate Vernalization Requirement

The flowering response of Dianthus gratianopolitanus Vill. ‘Bath's Pink’ was characterized after varying durations at vernalizing temperatures. Genetically identical clonally propagated plants were treated at 5 °C for 3, 6, 9, 12, or 15 weeks in Expt. I; at 0, 5, or 10 °C for 2, 4, 6, or 8 weeks in Expt. II; and at 0, 5, 10, or 15 °C for 1, 2, 4, 6, or 8 weeks in Expt. III. Dianthus gratianopolitanus ‘Bath's Pink’ exhibited a quantitative vernalization response after treatment at 0 to 10 °C and did not vernalize after 8 weeks at 15 °C, which was the longest duration tested. Complete flowering was achieved after 4 or more weeks at 0 °C, 3 or more weeks at 5 °C, and 8 weeks at 10 °C. Based on time to anthesis and node number at anthesis, the flowering response was saturated after vernalization treatment at 0 °C for 4 or more weeks and 5 °C for 3 or more weeks. However, maximum flowers at anthesis were produced after 8 weeks at 0 °C and 6 or more weeks at 5 °C. Flowering was delayed after the 8-week treatment at 10 °C compared with 6 or more weeks at 0 °C and 4 or more weeks at 5 °C. Based on the minimum vernalization duration required to achieve the maximum flowering response, the order of efficacy of vernalizing temperatures was 5 °C &gt; 0 °C ≫ 10 °C.

Daily Light Integral, Prevernalization Photoperiod, and Vernalization Temperature and Duration Control Flowering of Easter Cactus

Experiments were performed on Hatiora gaertneri (Regel) Barthlott ‘Jan’ and ‘Rood’ and H. ×graeseri (Wedermann) Barthlott ‘Evita’ to determine their flowering responses to 1) daily light integral (DLI) before and during vernalization; 2) 0 to 6 weeks of short-day (SD) or long-day (LD) photoperiods before vernalization at 10, 12.5, or 15 °C; 3) propagation from April to July; 4) timing of leveling before or during inductive treatments; and 5) SD photoperiods before vernalization under darkness at 0 to 10 °C. ‘Jan’ grown under elevated DLI before vernalization and low DLI during vernalization flowered more prolifically than plants grown under low DLI before vernalization or high DLI during vernalization at 15 °C. Six weeks of SD photoperiods before vernalization increased the number of buds per flowering phylloclade after vernalization at 10 °C and increased flowering uniformity when vernalization duration was insufficient at 10 °C or vernalization temperature was 12.5 or 15 °C. For plants flowering in January, propagation the previous April produced better flowering than propagation in May, June, or July. Removal of apical phylloclades during prevernalization SD or during vernalization was deleterious to flowering. Vernalization in the dark produced marginal flowering, but SD treatment before vernalization increased the percentage of apical phylloclades flowering, buds per flowering apical phylloclade, and percentage of plants flowering after dark vernalization. ‘Evita’ flowered more poorly than either ‘Jan’ or ‘Rood’. Collectively, the most uniform flowering in January occurred when plants were exposed to a sequence of 4 to 6 weeks of SD, vernalization at 7.5 to 15 °C for 8 weeks, then growth under LD for 7 weeks.

A model‐based framework for the phenotypic characterization of the flowering of Medicago truncatula

To facilitate the phenotypic characterization of Medicago truncatula, our aim was to provide a framework of analysis of flowering in response to environmental factors. The flowering of the line A17 was analysed in different conditions of temperature, duration of vernalization and photoperiod. Flowering was characterized using three descriptors at the axis level: the position of the first reproductive node (1RN), the date of beginning of flowering (DBF) and the florochron (RFa-1) corresponding to the reciprocal of the rate of progression of flowering along each axis. As for vegetative development, it was found that flowering could be analysed as a function of thermal time using a base temperature (Tb) of 5 degrees C. Vernalization displayed a sound impact on the flowering. For all the studied axes, increasing the duration of vernalization lowered the 1RN and hastened the DBF. By contrast, for most of the studied axes, RFa-1 was only slightly affected by vernalization. For the branch B0, RFa-1 was a genotypic constant when thermal time was used. Considering B0 as a reference axis, an ecophysiological model was developed to simulate the impact of environmental factors on the three components of flowering. Concrete practical applications of the model-based framework presented herein are proposed for helping the genetic and genomic studies of M. truncatula.

Sugar beet floral induction and fertility: effect of vernalization and day-length extension

There are great needs to establish a local breeding program for sugar beet to select genotypes tolerant to the environmental condition dominating Egypt. It is essential to establish a database of the required process needed to induce sugar beet to flower under the Egyptian conditions. This work was carried out during 2002– 2003 and 2003–2004 growing seasons to study the effect of vernalization duration and day-length extension on floral induction and fertility of some imported sugar beet cultivars. The experiment was carried out at Assiut University Experimental Farm at latitude of 27°N. Ten diploid cultivars imported from USA were used namely: C 14, C 146, C 205, C 211, C 221, C 261, C 283, C 9622, C 9720, US H11. Roots were grown in field for 5 months then vernalized at 4°C for three periods of 30, 45 and 60 days. The roots were then replanted in the field. Day-length extension treatment was secured by artificial illumination to extend day-length to 14 hours/day. The average light intensity above the soil was approximately 2222 Foot -candle. Extended day- length started 3 weeks after replanting and lasted for 45 days. Roots were also replanted under natural day-length conditions to serve as the second day- length treatment. The data recorder were; Bolting%, number of days from transplanting to bolting, pollen viability estimated as % of germinated pollen grains, single plant seed yield (gm), seed index (100 seeds), and seed germination%. The experimental design was a split block with 4 replicates. Each of the two day-length extension treatments was treated as a separate experiment. Within each experiment vernalization duration was assigned to the main plots and cultivars were allocated as the sub-plots. The results indicated that day-length extension and vernalization treatments had significant effect on the flowering of the cultivars. The response of the cultivars varied according to the combinations of the treatments. The results also indicated that the flowered cultivars maintained acceptable levels of pollen viability, seed setting and seed germination that could allow for the beginning of a breeding program. There are needs for further examination of other genetic materials to secure a successful sugar beet breeding program