Potted Sunflower Research Articles

Paclobutrazol Drenches Control Growth of Potted Sunflowers

Paclobutrazol drenches were applied at 0, 2, 4, 8, 16, or 32 mg a.i./pot to potted sunflowers (Helianthus annuus L. `Pacino') to determine its effect on growth. Plant height was shorter as paclobutrazol dose increased up to 16 mg; however, additional increases in dose had little effect on height. Severe height retardation of `Pacino' plants was evident at 16 and 32 mg. Plants treated with 2 mg of paclobutrazol were 17% and 25% smaller in diameter than untreated plants in Expts. 1 and 2, respectively. Plant diameter was smaller as paclobutrazol dose increased up to 16 mg, with additional increases in dose having little effect on plant diameter in Expt. 2. Plants treated with 16 or 32 mg of paclobutrazol exhibited phytotoxicity symptoms including crinkled leaves and stunted growth, and smaller and greener leaves. Sunflower plant growth was greater in the summer (Expt. 1) than in winter (Expt. 2). In the summer higher doses of paclobutrazol will be required than in winter for growth control. Marketable sized plants grown in 15- to 16.5-cm-diameter pots were produced with doses of paclobutrazol at 2 and 4 mg in both seasons, and doses up to 8 mg can also be used in summer for growth control.

Potted Sunflower Growth and Flowering Responses to Foliar Applications of Daminozide, Paclobutrazol, and Uniconazole

Plant growth retardant (PGR) foliar sprays (in mg·L−1) of daminozide at concentrations from 1,000 to 16,000; paclobutrazol from 5 to 80; and uniconazole from 2 to 32 were applied to `Pacino' potted sunflowers (Helianthus annuus L.) to compare their effectiveness at chemical height control. Plants were grown in 650-mL or 1.2-L pots. When the first inflorescence started to shed pollen, number of days from seeding until anthesis, total plant height measured from the pot rim to the top of the inflorescence, inflorescence diameter, and plant diameter were recorded. There was no significant difference in plant height between `Pacino' plants grown in 650-mL or 1.2-L pots. Total plant height, plant diameter, inflorescence diameter, and days until flowering were significant for the PGR treatment main effect. Marketable-sized plants grown in the 1.2-L pots were produced with uniconazole concentrations from 16 to 32 mg·L−1 or with daminozide concentrations from 4,000 to 8,000 mg·L−1. Paclobutrazol foliar sprays up to 80 mg·L−1 had little effect, and higher foliar spray concentrations or substrate drench treatments may be needed to effectively control height.

Non-Stomatal Inhibition of Photosynthesis Associated with Partitioning of the Recent Assimilates into Starch and Sucrose in Sunflower Leaves under Water Stress.

The effects of water stress on the photosynthesis (Pn) of potted sunflower Helianthus annuus L. plants were examined by monitoring the photosynthetic O2 evolution rates under saturated CO2 (10 kPa). These conditions eliminate stomatal limitation and partitioning of the recent assimilates into sucrose and starch in leaves was measured with decreasing leaf relative water content (RWC). Water-stressed leaves at RWC lower than 60% required at least 8 min pre-illumination at a saturated irradiance to reach the maximum O2 evolution rate (Pmax), compared to 2 min for non-stressed leaves, suggesting slower light-activation of enzymes involved in CO2 fixation in the Calvin cycle. Light-saturated photosynthesis and apparent quantum yield decreased with decreasing leaf RWC, but the former was inhibited more than the latter by the water stress. Pmax of both non-stressed and ABA-fed leaves required a very high CO2 pressure of 10 kPa to overcome stomatal closure but Pn never completely recovered in dehydrated leaves at RWC lower than 65%. We concluded that a non-stomatal inhibition played an important role in reducing photosynthesis of severely dehydrated leaves. Water stress increased sucrose content and decreased starch content in dehydrated leaves, leading to an increase in sucrose/starch ratio with decreasing RWC and Pmax. These results suggest that photosynthesis of water-stressed sunflower leaves was depressed on account of stomatal and non-stomatal limitations, which might be a feedback regulation of sucrose and starch syntheses influenced by water stress.

Pot Sunflower Growth and Flowering Responses to Foliar Applications of Daminozide, Paclobutrazol, and Uniconazole

Plant growth retardant (PGR) foliar spray treatments (mg•liter–1) of daminozide at 1000 to 16,000; paclobutrazol from 5 to 80; and uniconazole from 2 to 32 were applied to `Pacino' pot sunflowers (Helianthus annuus) to compare their effectiveness at chemical height control. When the first inflorescence opened, the number of days from seeding until flowering, total plant height measured from the pot rim to the top of the inflorescence, inflorescence diameter, and plant diameter were recorded. Total plant height, plant diameter, inflorescence diameter, and days until flowering were significant for the PGR treatment interaction. Marketable-sized plants grown in the 1.2-liter pots were produced with uniconazole concentrations between 16 and 32 mg•liter–1 or with daminozide concentrations between 4000 and 8000 mg•liter–1. Paclobutrazol foliar sprays up to 80 mg•liter–1 had little effect and higher concentrations or medium drench treatments should be considered.

Influence of Fertility on Plant Growth and Postharvest Quality of Pot Sunflowers

Pot sunflowers (Helianthus annuus cv. `Pacino') were fertigated on ebband-fl ow benches with 100 or 200 mg·liter–1 of N to determine the influence of fertility level on plant growth and postharvest quality in interior conditions. The fertilization rates were held constant from potting until day 45, then the fertilization rates were continued, decreased, or ceased on day 45 and day 55, giving a combination of nine fertilization subtreatments. At bloom, the number of days from potting to flowering, plant height, plant diameter, flower diameter were recorded, and the root medium of five replicates per treatment were analyzed to determine the nutrient status. Five replicates of each treatments also were moved into interior conditions with artificial lighting and were graded 5, 10, and 15 days after moving to evaluate the postharvest quality. There was no significant difference among fertilizer treatments for the number of days to flower, plant height, or flower diameter. Plants fertilized with 100 mg·liter–1 N from potting until day 45, in combination with a ceasing of fertilization on day 55, had significantly better plant grades when compared to plants grown with 200 mg·liter–1 N. Plants fertigated with 100 mg·liter–1 N also had a longer postharvest life and the number of days before the flowers wilted were significantly longer. Good-quality plants with longer postharvest life were produced with 100 mg·liter–1 N and by terminating fertilization 55 days after potting.

Efficacy of Paclobutrazol Drenches on Growth of Potted Sunflowers Grown in 16.5-cm Pots

Drench applications of plant growth retardant paclobutrazol were applied at 2, 4, 8, 16, or 32 mg a.i./pot, plus an untreated control to pot sunflowers (Helianthus annuus cv. `Pacino') to determine its effect as a chemical height control. All paclobutrazol concentrations applied significantly reduced plant height by »27% when compared to the untreated control, but excessively short plants were observed at 16 and 32 mg a.i./pot. Plant diameter was also significantly decreased by »16% at 2 and 4 mg a.i./pot of paclobutrazol, when compared to the untreated control. Flower diameter decreased by »4% at 2 and 4 mg a.i./pot of paclobutrazol, but only concentrations ≥4 mg a.i./pot were significantly different from the untreated control. Paclobutrazol concentrations had no effect on days from potting to flowering. Drench concentrations of 2 and 4 mg a.i./pot of paclobutrozol produced optimum height control in relation to 16.5-cm-diameter pot size used.

Phytotoxic effects of industrial and sewage waste waters on growth, chlorophyll content, transpiration rate and relative water content of potted sunflower plants

Waste water coming from two factories, namely Manquabad (fertilizer) and Bani Qura (detergents and oils) factory and Arab El-Madabegh sewage effluents were determined for their phytotoxicities and physicochemical properties. The effect of the waters on the growth, chlorophyll content, transpiration rate and leaf relative water content of sunflower plants was undertaken in pots. In addition, the phytotoxicity present in the waste waters on embryonic radicle growth was also studied. The experiments were repeated each month from January to June, 1992. The three waste waters exhibited significant phytotoxic effects on the radicle growth of sunflower. The phytotoxicity varied with monthly sampling. The waste water from the fertilizer factory (Manquabad) collected in February, May and June showed almost 100% inhibition on the radicle growth, while January and April sampling had a stimulatory effect. Most of the tested water exhibited significant inhibition on shoot growth. Root growth was significantly enhanced by Arab El-Madabegh sewage water collected in February, March and April and was suppressed in the other three months. The three waste waters showed inhibitory effect on chlorophyll content. The inhibition was very high in the January sampling. Chlorophyll stability to heat was significantly lower in February and March and higher in May and June water-treated plants. Generally waste water-treated plants showed a lower transpiration rate than the control (tap water). Leaf relative water content of plants grown in the waste waters was significantly lower in May and June collected water than in the other four months collections. The physicochemical analysis of the waste waters revealed that the amount of Na+, K+, Ca+2 Zn+2, Cu+2, Iron, Cl−, SO4−2 and the degree of electrical conductivity were often above the limits of the standard for irrigation water for agricultural land, and some of these properties would be severely detrimental to crop growth. Generally waste water coming from the Manquabad fertilizer factory consistently revealed the highest inhibition, Bani Qura detergents and oils factory the second and Arab El-Madabegh sewage the least.

Including the heat storage term in sap flow measurements with the stem heat balance method

The importance of the change in stem temperature and therefore the heat storage term in the stem heat balance method of measuring sap flow is examined. Results from a range of measurements on a model stem, potted sunflower plants in a glasshouse, and Guiera senegalensis shrubs in the Sahel, Niger, are presented. A novel analysis of the heat balance in zero flow conditions allows the accurate determination of the gauge radial conductance and the stem segment heat capacity, both of which are required for accurate sap flow measurement with good dynamic resolution in low flow conditions. In high sap flow conditions the change in heat storage constitutes only a small component of the balance, and can be neglected, especially for small stems. The improved accuracy and dynamic resolution for stems of any size if heat storage is included allowed the measurement of low night-time flows during rehydration, and of redistribution of water between stems of G. senegalensis bushes in the field following rain.

Comparative Study of the effects of applied indoleacetic acid and horizontal orientation of the primary shoot, upon internode extension and petiole orientation inHelianthus Annuus, and the modifying influence of gibberellic acid

1. It is shown that subjecting potted sunflower plants to alternating periods of horizontal and erect orientation, with or without occasional rotation of the primary axis, results in a marked reduction in the rate of stem extension growth, the development of petiole epinasty and increased downward orientation of the leaves. Neither of these symptoms appears to be a direct gravitational response to the horizontal position. 2. It is demonstrated that the petiole epinasty is probably a correlative phenomenon while the inhibition of extension growth apparently results from the development of a factor which takes 24–48 hours to reach maximum intensity after the application of the horizontal stimulus. 3. Similar responses can be induced in permanently erect plants by applying IAA in amounts greater than about 5 μg/plant. 4. The application of GA to either horizontally stimulated or IAA treated plants, alleviates both the petiole epinasty and the inhibition of extension growth. 5. The results obtained are in agreement with the hypothesis that placing the shoot in the horizontal position causes an increase in the concentration of stem auxin and that this induces petiole epinasty and brings about a reduction in stem extension growth. In view of the alleviating influence of GA, it is suggested that the postulated increase in stem auxin may effect extension growth by reducing the natural gibberellin level in the stem to suboptimal values.