Possible role of non-structural carbohydrates in flower induction in strawberry

Summary

Flower-induction is the event that initiates the transition of a vegetative apex into a floral apex in response to an environmental or developmental cue. Under flower-inducing conditions, biochemical or physiological changes can be recognised. One possible change that could occur is in sugar content. In this study, levels of non-structural carbohydrates (e.g., sucrose, glucose, fructose and starch) were measured in shoot tips, leaves and roots of strawberry (Fragaria ananassa cv. ‘Kordestan’) under flower bud-inducing conditions, and compared with non-induced plants. Runner plants were potted and grown for 4 weeks under non-inducing conditions (31º/25°C day/night; 16 h daylength). Half of the plants were then put under flower-inducing conditions (25°/15°C day/night; 8 h daylength) for 3 weeks. Samples for carbohydrate analysis were taken from induced and non-induced plants every 3 d over 3 weeks, and sucrose, glucose and fructose contents were determined by HPLC, and starch concentrations by the anthrone method. The most abundant soluble sugar, in all organs tested, was sucrose. Sucrose levels in shoot tips and leaves decreased at the beginning of the induction treatment, but soon increased to the levels recorded in non-induced plants. Fructose increased markedly in shoot tips of induced plants 3 d after the start of the short-day treatment, and declined thereafter. Starch contents in shoot tips, leaves and roots of non-induced strawberry plants were higher than those in induced plants on most sampling dates. From the results of this study, it appears that soluble carbohydrate contents in different organs of June-bearing strawberry may have a decisive role on flower-bud induction.     

Histone H4 gene expression and morphological changes on shoot apices of strawberry (Fragaria × ananassa Duch.) during floral induction

To investigate flower induction in June-bearing strawberry plants, morphological changes in shoot apices and Histone H4 expression in the central zone during flower initiation were observed. Strawberry plants were placed under flower inducible, short-day conditions (23 °C/17 °C, 10 h day length) for differing number of days (8, 16, 20, 24 or 32 days) and then these plants were transferred to non-inducible, long-day conditions (25 °C/20 °C, 14 h day length). The shoot apices of plants placed under short-day conditions for 8 days were flat, similar to shoot apices of plants in the vegetative phase of development, and Histone H4 was not expressed in the central zone during the experimental period. On the other hand, the shoot apices of plants placed under short-day conditions for 16 days remained flat, similar to shoot apices of plants placed under short-day conditions for 8 days, but Histone H4 was expressed in the central zone at the end of the short-day treatment. Morphological changes in the shoot apices of these plants were observed 8 days after the change in day-length. These plants developed differentiated flower organs after they were grown for another 30 days under long-day conditions. These results indicate that changes in the expression pattern of the Histone H4 gene occur before morphological changes during flower induction and that the expression of the gene in the central zone can be used as one of the indicators of the flowering process in strawberries.     

Effect of plant growth temperature on membrane lipids in strawberry (Fragaria × ananassa Duch.)

Changes in membrane lipid composition are important in the acclimation of plants. The influence of four day/night growing temperature combinations (18/12, 25/12, 25/22, and 30/22 °C) on membrane lipids of ‘Earliglow’ and ‘Kent’ strawberry (Fragaria × ananassa Duch.) were studied. The monogalactosyl diglyceride (MGDG) and digalactosyl diglyceride (DGDG) were the major galactolipids in the strawberry leaves. ‘Earliglow’ contained a higher amount of galactolipids in the leaves than ‘Kent’. The major phospholipids in the strawberry leaves, roots, and fruit were phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE). PC and PE were the two predominant phospholipids in the strawberry. The leaves and fruit of ‘Earliglow’ contained higher amounts of phospholipids compared to those of ‘Kent’, whereas ‘Kent’ strawberry roots had higher phospholipids. Palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2), and α-linolenic (C18:3) acids were major fatty acids in galacto- and phospholipids of the ‘Earliglow’ and ‘Kent’ strawberry. PC is very rich in linolenic acid in leaves compared to the fruit and root tissues. PC had the highest ratio of unsaturated to saturated fatty acids among all phospholipids. There was a significant increase in the content of galactolipids (MGDG, DGDG) and phospholipids (PC, PI, PG and PE) and unsaturation of their fatty acids in the cool day/night growth temperature. Increasing day/night growth temperatures decreased MGDG/DGDG ratios. The shifts in saturation and composition of fatty acids observed with strawberry may be an adaptation response of plants to the temperature changes.     

Changes in morphological phenotypes and essential oil components in lavandin (Lavandula × intermedia Emeric ex Loisel.) transformed with wild-type strains of Agrobacterium rhizogenes

Hairy roots were induced from leaf-derived calli of lavandin (Lavandula × intermedia Emeric ex Loisel.) by infection with wild-type strains of Agrobacterium rhizogenes, A-5 (MAFF 02-10265) and A-13 (MAFF 02-10266). A-5-inoculated calli formed hairy roots more efficiently than A-13 ones. The transgenic shoots could be obtained from hairy root segments mediated by each Agrobacterium strain. However, different plant growth regulators were required for efficient adventitious shoot formation in each strain. In A-5, the most efficient adventitious shoot formation rate of 23.8% was observed in a medium with 4.4 × 10⁻⁶ M of 6-benzylaminopurine. On the other hand, a significantly higher rate of 13.2% was detected in a medium with 4.0 × 10⁻⁷ M of N-(2-chloro-4-pyridyl)-N′-phenylurea in A-13. Most of the regenerated plants showed dwarfism with closed internodes and extensive lateral branching, which were typical characteristics of ‘hairy root syndrome’. On the other hand, only nine of the 45 regenerated plants formed flower buds in early June, a delay of about one month compared with nontransgenic regenerated plants. The floral stalks and spikes of these plants were very short, resulting in a compacted form. Many regenerants showed a significantly lower productivity of essential oil than nontransgenic regenerants. Moreover, the relative percentage of the linalyl-cation-derived compounds, linalool and linalyl acetate, decreased in most of the regenerated plants. Compact plants with the ability of flower bud formation are assumed to be valuable not only for lavandin breeding, but also for clarifying the interaction between rol genes expression and essential oil production.     

Prolonged high-temperature exposure differentially reduces growth and flowering of 12 Viola × wittrockiana Gams. cvs

Many cool season garden crops, including Viola × wittrockiana Gams. (pansy), exhibit reduced flowering outdoors during the warm summer months. Twelve pansy cultivars varying in summer garden performance were grown under either 20 ± 1.5 or 30 ± 1 °C (air temperature) to determine growth and flowering responses to prolonged high-temperature exposure and to identify selection criteria to screen pansies for flowering heat tolerance. Increasing temperature from 20 to 30 °C increased leaf number below the first flower on ‘Crystal Bowl Primrose’ and ‘Skyline White’ only. Flower bud number reduction at 30 °C versus 20 °C varied from 20% for ‘Crystal Bowl Purple’ to 77% for ‘Majestic Giants Red and Yellow’. Flower diameter reduction at 30 °C versus 20 °C ranged from 14% for ‘Skyline Beaconsfield’ to 44% for ‘Super Majestic Giants Ocean’. The percentage reduction in total color (flower number × estimated flower area) ranged from 60% for ‘Crystal Bowl Primrose’ to 88% for ‘Majestic Giants Rose Shades’. Based on a weighted base selection index, ‘Super Majestic Giants Canary’ and ‘Delta Yellow’ were identified as the most heat-tolerant cultivars, while ‘Super Majestic Giants Ocean’ and ‘Majestic Giants Rose Shades’ were identified as the most heat-sensitive. In a second experiment, root and shoot dry mass were determined after 10, 20, or 30 d when grown at 20 or 30 °C. Relative growth rate and root:shoot ratio were also calculated. After 30 d, ‘Crystal Bowl Primrose’, ‘Crystal Bowl Sky Blue’ and ‘Skyline White’ relative growth rates were lower at 30 °C versus 20 °C. Root:shoot ratio on day 30 was lower at 30 °C compared to 20 °C for six cultivars, but similar across temperature for five cultivars and higher for ‘Crystal Bowl Primrose’. Flower bud number at first flower was positively correlated with branch number, shoot dry mass at flowering, but not correlated with root dry mass at flowering, and negatively correlated with flower diameter and root:shoot ratio (either at flowering, or after 10, 20 or 30 d at 30 °C), suggesting that these traits may be useful when screening pansies for flowering heat tolerance.     

Interactions of photoperiod,temperature, duration of short-day treatment and plant age on flowering of Fragaria x ananassa Duch. cv. Korona

The effects of photoperiod (10, 12, 16, 20 or 24 h), day-temperature (12, 15, 18, 24 or 30 °C), the number of short days (14, 21 or 28 days), plant age (4, 8 or 12 weeks) and their interactions on flower and inflorescence emergence were investigated in strawberry cv. Korona. No flowers emerged in plants exposed to photoperiods of 16, 20 or 24 h or to a short-day treatment for 14 days. All plants exposed to short days at daily photoperiods of 10 or 12 h for 21 days or longer, emerged flowers at temperatures between 12 and 18 °C. A further increase in temperature led to a drastic decrease in the total number of flowers per plant. A short-day treatment (10 or 12 h photoperiod) of 28 days resulted in highest numbers of inflorescences and flowers per plant, while a short-day treatment of 21 days resulted in the highest numbers of flowers per inflorescence. Complete flower induction was observed in only 4-week-old runner plants. The number of inflorescences and the number of flowers per inflorescence increased with plant age. However, the start of flowering was delayed with increasing plant age.     

Temporal dynamics of nutrient and carbohydrate distribution during crop cycles of Rosa spp. ‘Kardinal’ in response to light availability

Rose plants that are flush harvested exhibit episodic growth patterns. During these crop cycles little biomass accumulation occurs immediately following harvest; and as new shoots emerge a period of rapid shoot growth and biomass accumulation occurs. The temporal changes in whole-plant nutrient and carbohydrate distribution during these crop cycles and the role of storage in new shoot growth are not well documented. The objective of this project was to quantify N, P, K, and total non-structural carbohydrates (TNC) distribution in roots, base stems, base leaves, and new shoots during crop cycles in response to light availability. Plants were grown in solution culture under high or low light (mean daily light integral 45.3 or 13.1 mol m⁻² d⁻¹, respectively) during 30–35 day crop cycles. Every five days destructive sampling was used to determine biomass and N, P, K, and TNC concentration of rose plant compartments. N and TNC accumulated in base plant compartments during the first ten days of the crop cycles. N, P, K, and TNC in base plant compartments declined during days 10–25 during a crop cycle concurrent with the rapid growth of flower shoots. N, P, and K storage in base plant parts represents 27, 22, and 24% of the potential N, P, and K required by flower shoots under high light; and 19, 21, and 22% of requirements under low light. TNC storage in base plant parts represents 4–10% of the final biomass of flower shoots. Mobilization of N, P, K, and TNC stored from base plant parts appears to be important during the stage of rapid flower shoot growth when absorption by roots or photosynthesis by shoots was insufficient to meet flower shoot demands. Plant carbohydrate status was improved under high light conditions; storage of N and TNC declined under low light.     

Influences of day and night temperatures on flowering of Fragaria x ananassa Duch., cvs. Korona and Elsanta,at different photoperiods

The effects of photoperiod (12, 13, 14, 15 or 16 h), day temperature (12, 15, 18, 24 or 27 °C) and night temperature (6, 9 or 12 °C) and their interactions on flower and inflorescence emergence were investigated by exposing 4 week old runner plants of strawberry cvs. Korona and Elsanta during a period of 3 weeks. A daily photoperiod of 12 or 13 h resulted in the highest number of plants with emerged flowers. A photoperiod of 14 h or more strongly reduced this number, while no flowers emerged at a photoperiod of 16 h. Plants exposed to photoperiods of 12 or 13 h flowered earlier and had longer flower trusses. A day temperature of 18 °C and/or a night temperature of 12 °C were optimal for plants to emerge flowers and resulted in the shortest time to flowering. A night temperature of 6 °C strongly reduced the number of plants that emerged flowers, especially when combined with lower day temperatures. Photoperiod and temperature had no effect on the number of inflorescences, all flowering plants produced on average one inflorescence. The number of flowers on the inflorescence increased with decreasing day temperature and when photoperiod was raised from 12 to 15 h. In general, ‘Korona’ was more sensitive to photoperiod and temperature as ‘Elsanta’, and had a lower optimal day temperature for flower emergence. Results of this experiment may be used to produce high quality plant material or to define optimal conditions when combining flower induction and fruit production.     

Endogenous and exogenous polyamines in the organogenesis in Curcuma longa L.

The present work evaluated the development of different Curcuma longa L. explants (leaves basis, root tips and ancillary buds from rhizome) stimulated by exogenous polyamines, combined with naphtalen-acetic acid (NAA) or with 6-benzyl-aminopurine (BAP), to produce callus and its subsequent differentiation. The explants, isolated from field plants, were previously subjected to a basic cleaning method and were inoculated onto Murashige and Skoog culture medium (MS) [Murashige, T.S., Skoog, F., 1962. A revised medium for rapid growth and bioassays with tobacco tissue culture. Physiologia Plantarum 15, 473–497] supplemented with NAA (2.0 mg L⁻¹). Buds were subjected to different treatments, with or without 5.0 and 10.0 mmol L⁻¹ exogenous polyamines (mixture of putrescine:spermine:spermidine, 1:1:1) combined with NAA. The calluses obtained were transferred into the same medium, supplemented with the mixture of polyamines combined with BAP, in order to induce plant differentiation. For C. longa, buds were the most efficient explants for callus induction (p < 0.05). The application of exogenous polyamines (5.0 and 10.0 mmol L⁻¹) produced the most developed callus, with numerous roots. The medium supplemented with 10 mmol L⁻¹ polyamine mixture, combined with BAP, induced good regeneration, producing vigorous plants and excellent shoot formation.Polyamines addition promoted the formation of callus, roots and leaves, representing an important factor in the determination of indirect organogenesis in C. longa L., and putrescine content may be considered a valuable marker of the differentiation process in this specie, as well as the enzyme peroxidase.     

Role of 24-epibrassinolide in mitigating the adverse effects of salt stress on stomatal conductance,membrane permeability,and leaf water content,ionic composition in salt stressed strawberry (Fragaria × ananassa)

In order to study the effect of brassinosteroids on the amelioration of the inhibitory effect of salinity on strawberry plants, a short-term experiment was conducted in greenhouse to test different concentrations of 24-epibrassinolide (24-EBL) (0.0, 0.5, and 1 μM) by foliar application on some agro-physiological properties, such as shoot dry weight, and root dry weight, stomatal conductance (SC), leaf relative water content (LRWC), leaf chlorophyll reading values (LCRV) and membrane permeability (MP) of strawberry ‘Fern’ and ‘A6’ cultivars irrigated with salt water (35 mM NaCl). 24-EBL solutions were applied twice during late afternoon hours with 7 d intervals using a hand-held sprayer. Plant shoot dry weight, root dry weight, SC, LRWC and LCRV were reduced by 29–33%, 45–15%, 71–55%, 11–13%, and 12–13% for ‘A6’ and ‘Fern’ cultivars at 35 mM (without 24-EBL applied), respectively, as compared to the nonsaline treatment, but MP increased 40% and 12%. An exogenous supply of 24-EBL was found to be successful in alleviating of the inhibitory effects of salt stress on plant growth parameters and nutrient contents. 24-EBL (1 μM) application under saline condition significantly increased shoot and root dry matter, SC, LRWC and LCRV of plants, and alleviation effects of 1 μM 24-EBL application was 20%, 15%, 122%, 5.8%, and 10.9% for ‘A6’ and 47%, 8.0%, 83%, 33.3% and 6.0% for ‘Fern’ cultivars, respectively. Macro-micro element content of plant leaf and root increased with increase 24-EBL except for Na under salinity stress. These results support the view that supplementary 24-EBL application can overcome the effects of salinity stress on plant growth and growth parameter under saline conditions.     

Interaction of short day and timing of nitrogen fertilization on growth and flowering of ‘Korona’ strawberry (Fragaria × ananassa Duch.)

The effects of timing of nitrogen (N) fertilization relative to the beginning of a 4-week floral-inducing short-day (SD) period have been studied in ‘Korona’ strawberry plants under controlled environment conditions. Groups of low fertility plants were fertilized with 100 ml of calcium nitrate solution for 3 days a week for a period of 3 weeks starting at various times before and at the beginning of the SD period, as well as at different times during the SD period. All plants, including SD and long day (LD) control plants, received a weekly fertilization with a low concentration complete fertilizer solution throughout the experiment. Leaf area, fresh and dry matter increments of leaves, crowns and roots, as well as leaf chlorophyll concentration (SPAD values) were monitored during the experimental period. A general enhancement of growth took place at all times of N fertilization. This was paralleled by an increase in leaf chlorophyll concentration, indicating that the control plants were in a mild state of N deficiency. When N fertilization was started 2 weeks before beginning of the SD period, flowering was delayed by 7 days, and this was gradually changed to an advancement of 8 days when the same treatment was started 3 weeks after the first SD. The amount of flowering was generally increased by N fertilization although the effect varied greatly with the time of N application. The greatest flowering enhancement occurred when N fertilization started 1 week after the first SD when the number of flowering crowns and the number of inflorescences per plant were more than doubled compared with the SD control, while fertilization 2 weeks before SD had no significant effect on these parameters. Importantly, the total number of crowns per plant was not affected by N fertilization at any time, indicating that enhancement of flowering was not due to an increase in potential inflorescence sites. No flowering took place in the control plants in LD. Possible physiological mechanisms involved and practical applications of the findings are discussed.     

The effect of nitrate and plant size on nitrate uptake and in vitro nitrate reductase activity in strawberry (Fragaria × ananassa cv. Selva)

Nitrogen plays a major role in the growth and yield of strawberry. For optimizing nitrogen fertilizer application, it is necessary to understand the response of strawberry to nitrogen supply. The objective of this study was to determine the effect of nitrate supply and plant size on strawberry nitrate uptake and nitrate reductase activity (NRA). Strawberry plants cv. Selva were grown under growth chamber conditions in nutrient solutions containing 0, 0.1, 0.25, 0.7 or 4 mM nitrate. Cumulative nitrate uptake increased with the increase in nitrate supply. Increasing nitrate concentrations from 0 to 0.25 mM decreased leaf NRA; however, further increases to 4 mM nitrate restored NRA to activities observed at 0 mM nitrate. The activity of NADH- and NADPH-dependent NR was similar at every external nitrate concentration. Activity of NR was greater in the smallest plants and decreased as plant size increased. However, increasing external nitrate concentration increased nitrate uptake, but had not the same effect on nitrate reductase activity, showing that NRA and nitrate uptake are not necessarily correlated.     

Regulation of skin color in ‘Aki Queen’ grapes: Interactive effects of temperature,girdling, and leaf shading treatments on coloration and total soluble solids

The interactive effects of temperature, girdling, and leaf shading treatments on the total soluble solids (TSS) content and coloration of ‘Aki Queen’ (Vitis labruscana) grapes were investigated. The TSS contents of berries were significantly higher in girdled plants than in plants with shaded leaves. Anthocyanin accumulation was greater at lower temperature (21 ± 2 °C) than at higher temperature (31 ± 2 °C) in both control and girdled plants, but anthocyanins did not accumulate in plants with shaded leaves at either temperature. Temperature did not influence TSS content. These results suggest that a high enough TSS content promotes anthocyanin synthesis under low temperature during maturation of ‘Aki Queen’ grape.     

Effects of photoperiod on shoot elongation and endogenous gibberellins in the glasshouse carnation

Plants of glasshouse carnation were grown in photoperiodic cycles comprising 8 h natural daylight followed by either 16 h of darkness (short-day treatment) or by 16 h of low-intensity lighting from tungsten filament lamps (continuous-light treatment). When plants were transferred from short days to the continuous-light treatment, rates of shoot elongation were increased and flower initiation was promoted. Shoot tips of plants grown in continuous light yielded greater amounts of diffusible gibberellin-like substances than shoot tips of plants grown in short days. Yields of diffusible gibberellins increased with increases in the duration of the continuous light treatment up to 28 days, by which time flower initials were present. Application of GA₃ to the plants resulted in increased rates of shoot elongation, but no effect on flowering was observed.     

Gibberellic acid influences the production of malformed and button berries,and fruit yield and quality in strawberry (Fragaria × ananassa Duch.)

Experiments were conducted to observe the effects of foliar application of gibberellic acid on vegetative growth, flowering, fruiting and various disorders in ‘Chandler’ strawberry. GA₃ (75 ppm) was applied to the strawberry plants either during mid-November (at fruit bud differentiation stage), or mid-February (pre-flowering stage) or at both times. Fruit under control were sprayed with tap water only. Observations were recorded on vegetative attributes like crown height, crown spread, petiole length, leaf number, leaf area; flowering and fruit set, fruit size; production of albino, malformed and button berries, total yield and marketable fruit yield and quality parameters, like juice content, TSS, ascorbic acid contents, acidity etc. Results indicated that GA₃ (75 ppm) spray either during mid-November or mid-February or at both times has favourably influenced all vegetative attributes of ‘Chandler’ strawberry over control. Similarly, fruit set was increased, and production of malformed and button berries was reduced, but albinism remained unaffected. Although individual berry weight was reduced slightly, but fruit number, total as well as marketable yield was increased tremendously over control with no adverse effect on fruit quality parameters. In all, spraying GA₃ both during mid-November and mid-February was much more effective in achieving the desirable results than single application of GA₃ either during mid-November or mid-February.     

Relationship between tipburn and leaf mineral composition in strawberry

Malformation of emerging leaves with distortion of leaf tips, a condition known as tipburn, is frequently observed in strawberry. Calcium (Ca) deficiency has been considered the main cause of tipburn. The aim of the present study was to analyse the relationship between leaf mineral composition and the incidence of tipburn in three short-day strawberry (Fragaria x ananassa Duch.) cultivars (‘Ventana’, ‘Camarosa’ and ‘Candonga’) submitted to different concentrations of Ca. The studies were conducted in a hydroponic system in a greenhouse. Calcium was added as Ca(NO₃)₂ at 2 mM, 3 mM, 4 mM and 5 mM. A completely randomized block design (4 Ca concentrations × 3 cultivars) with three replications was used. Each replicate consisted of 12 plants grown in a polyethylene bag (100 cm × 18 cm × 3 cm) filled with coconut peat. Crown diameter and tipburn incidence were evaluated throughout the experimental period, and at the end of the experiment leaf mineral composition was assessed. In general, plants with larger crown diameters had a greater incidence of tipburn. The ‘Candonga’ cultivar had the smallest incidence of tipburn, while the ‘Camarosa’ and ‘Ventana’ cultivars were more susceptible. There was no correlation between level of Ca applied and incidence of tipburn. The incidence of tipburn was associated with foliar K:Ca and K:Mg ratios. Ratios above 3.40 for K:Mg and 1.77 for K:Ca represented a risk of more than 50% of tipburn incidence, when overall means for all cultivars and levels of Ca were used.     

Aneuploid strawberry (2n = 8x + 2 = 58) was developed from homozygous unreduced gamete (8x) produced by second division restitution in pollen

Unreduced gamete formation is significant in the evolutionary development of complex polyploidy series found in wild strawberry, genus Fragaria (Rosaceae). Also, it is important for genetics and breeding in strawberry plants to elucidate the mechanism of unreduced gamete formation. The objective of this study was to search for ploidy anomalies resulting from artificial diploid × octoploid crosses, and examine the mechanism through which these unreduced gametes were produced. Five everbearing cultivars of Fragaria vesca L. diploid (2n = 2x = 14) were crossed with pollen from six June-bearing cultivars of Fragaria × ananassa Duch., octoploid (2n = 8x = 56). A total of 3000 mature seeds, 100 from each of the 30 parental combinations were sown at 23 °C/20 °C (day/night) under artificial lighting with a 16 h day. The seedlings were transplanted to pots and grown in a greenhouse. Reproductive and morphological observations, flow cytometry analyses, chromosome counts and DNA analyses using CAPS markers were performed to identify the genetic background of the offspring. Most of the seed (79%) did not germinate or died soon after germination. Of the seedlings produced, 7% seemed to be pure F. vesca based on morphological characteristics, flow cytometry analyses and chromosome counts; 14% were pentaploids (2n = 5x = 35), 0.1% were hexaploids (2n = 6x = 42), and 0.03% (one individual) was aneuploid (2n = 8x + 2 = 58). Electrophoresis banding patterns obtained by CAPS marker analysis were heterozygotic in the 8x pollen parent but homozygotic in the aneuploid progeny. Judging from the chromosome counts and the CAPS marker analysis, the aneuploid was the result of a homozygous unreduced pollen grain (8x) crossed with an incomplete chromosome compliment from the egg. Because of the homozygosity, the unreduced male gamete must have been derived from second division restitution (SDR) in the octoploid pollen parent.     

Potent herbicidal activity of Inula crithmoïdes L.

Aqueous (10, 20, 30 and 40 g/L) and organic (hexane, chloroform and methanol, at 3000 and 6000 ppm) extracts of Inula crithmoïdes L. (roots, stems, leaves and flowers) were evaluated for their allelopathic activities on radish, lettuce, peganum and thistle. Pot cultures were conducted by incorporation of I. crithmoïdes leaves and flowers powder (1.25 and 2.5 g/kg) in soil and by irrigation with their aqueous extracts at 40 g/L. PEG (polyethylene glycol) solutions, with similar osmotic potentials of aqueous extracts, at the highest concentration, were without effect on target species, this eliminates the extracts osmotic effect. Germination index was not affected by root and stem extracts and significantly decreased by the two other ones. For growth, leaf and flower extracts had the most significant toxicity at 40 g/L, inducing up to a total inhibition. For organic extracts, a strong toxicity was recorded for the three fractions at 6000 ppm, thistle seedling growth was more sensitive, especially to chloroform fractions. Soil incorporation of residues (at 2.5 g/kg) significantly decreased root (35–100%) and shoot (0–100%) length of target species. Irrigation soil with leaves and flower aqueous extracts was harmful for peganum and thistle, respective inhibition percentages were 100% and 66.5%. I. crithmoïdes may be favorably used for incorporating in agricultural systems for sustainable weed management.     

Influence of ventilation and sucrose on growth and leaf anatomy of micropropagated potato plantlets

Potato single nodes were cultured in vessels containing MS medium supplemented with 10, 20 and 30 g/l of sucrose. Vessels were closed with a clear polypropylene lid with or without 10 mm microporous polypropylene membrane. Sucrose concentration significantly increased plantlet height, shoot fresh weight and chlorophyll a content. Plantlets grown in ventilated vessels were significantly shorter, had lower shoot fresh weight and higher shoot dry weight than those in non-ventilated vessels. The highest leaf chlorophyll a content (21.83 mg/g fresh weight) was found in plantlets grown in ventilated vessels using MS medium with 20 g/l of sucrose, whereas those grown on medium with 10 g/l of sucrose had the highest chlorophyll b content (24.00 mg/g fresh weight). Total chlorophyll content was significantly higher when plantlets were grown in ventilated vessels containing medium with 10 or 30 g/l sucrose than in non-ventilated vessels. There was no significant difference in total chlorophyll content among plantlets grown in ventilated vessels with different concentrations of sucrose. Stomatal density was significantly lower when plants were grown under ventilated conditions. Leaf replica examination showed that stomata under non-ventilated condition were spherical with wide openings whereas, those in ventilated vessels were elliptical with narrow openings. Plantlets grown in non-ventilated vessels had thinner leaves and failed to build up a distinct defined upper epidermis, palisade parenchyma layer and spongy cells. On the other hand, leaves under ventilated conditions showed comparatively well organized layers with small intercellular space. The vascular system of leaves under the ventilated conditions demonstrated very well developed xylem unlike leaves under non-ventilated conditions. Thus, ventilated vessels with the 20 g/l of sucrose under ambient CO₂ in the growth room could successfully promote photomixotrophic culture and produce healthy plantlets.