Levels Of Paclobutrazol Research Articles

Effect of paclobutrazol and salinity on ion leakage, proline content and activities of antioxidant enzymes in mango ( Mangifera indica L.)

A study was conducted to investigate the effects of paclobutrazol (PBZ) on ion leakage (IL), proline content and activities of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) of 1-year-old ‘Olour’ mango plants subjected to NaCl stress. Plants were treated with two levels of salt, i.e., 0.0 g NaCl (control) and 25 g NaCl/25 kg soil and three levels of paclobutrazol (PBZ) solution (0.0 (control), 750 and 1500 mg/l). Ion leakage, proline content and activities of antioxidant enzymes were significantly altered by both salinity and PBZ treatments. Results indicated that PBZ (1500 mg/l) mitigated the salinity stress and reduced ion leakage of mango seedlings by 64% over non-PBZ-treated salinised plants. PBZ upregulated the endogenous proline content and salinised plants treated with PBZ (1500 mg/l) had 17% higher proline content than salinised plants without PBZ treatment. Higher antioxidant enzyme activity was also observed in salinised plants treated by PBZ than salinised plants without PBZ treatments. Moreover, higher dose of PBZ (1500 mg/l) resulted in higher activity of these enzymes in mango leaves. In comparison to salinised plants without PBZ treatment, salinised plants treated with PBZ (1500 mg/l) had higher SOD (24%), CAT (46%) and POD (163%) activities. Our results suggest that PBZ application under salt stress conditions alters the equilibrium between free radical production and enzymatic defense reactions in mango by enhancing the proline content and free radical scavenging capacity.

Effect of the Growth Regulator Paclobutrazol on Growth of the Bacterial Pathogen Xylella fastidiosa Xylella fastidiosa

Xylella fastidiosa is a fastidious, xylem-limited, insect-transmitted, bacterial plant pathogen with a wide host range that causes bacterial leaf scorch (BLS) in shade trees. BLS is a chronic disorder characterized by late season leaf scorch and dieback and is common in urban and suburban areas of the mid-Atlantic and southeast United States. BLS has been recognized since the 1980s and attempted treatments have included antibiotics and plant growth regulators. Application of paclobutrazol (PBZ), a diastereomeric triazole with both fungistatic and growth regulation properties, has been observed to alleviate symptoms of BLS, but it has not been established whether PBZ has a direct effect on the organism. In this study, we investigated the effect of PBZ on in vitro growth of two X. fastidiosa isolates. Our results showed no significant effect of PBZ on colony growth of X. fastidiosa at the manufacturers recommended rate of 20 ‘ºg/mL ’àí1. However, significant reductions in bacterial growth were observed at a rate of 200 ‘ºg/mL ’àí1, indicating that high levels of PBZ may have a direct effect on the growth of X. fastidiosa. This direct effect and growth regulator effects of PBZs suggest that PBZ may provide a promising treatment for BLS in shade trees.

Investigation of Fungicidal Properties of the Tree Growth Regulator Paclobutrazol to Control Apple Scab

Paclobutrazol (PBZ) as a systemic fungicide for control of apple scab (Venturia inaequalis) was investigated in mature (cv. Hopa and Snow Drift) and young sapling (cv. Indian Magic) crabapples (Malus spp.). Treatments consisted of a control and PBZ applied to mature trees at one or two times the recommended rate in April 2002 using the basal drench method. Saplings received either foliar or soil drench applications of PBZ, or foliar applications of propiconazole. Disease assessments of mature trees showed that apple scab symptoms in treated trees were as severe as in untreated ones in the year of treatment but were reduced slightly the year after treatment in ‘Hopa’ and the third year after treatment in ‘Snow Drift.’ Growth reduction occurred in all treated trees, suggesting that the PBZ levels needed for growth reduction were not sufficient to control apple scab in the year of treatment. In contrast, a one-time foliar application of PBZ reduced apple scab incidence to levels found in ‘Indian Magic’ saplings treated every 2 weeks with propiconazole, a fungicide and application method commonly recommended for apple scab control. Delayed uptake and insufficient transport of PBZ to the foliage of mature trees after root drench treatments may account for the lack of apple scab control in the years after treatment, even though growth suppression occurred.

Indução do florescimento e crescimento de tangerineira 'Poncã' (Citrus reticulata Blanco) em função da irrigação e da aplicação de paclobutrazol

O experimento foi conduzido na Faculdade de Ciências Agronômicas - UNESP/Câmpus de Botucatu (SP), com o objetivo de avaliar o florescimento fora de época e o crescimento vegetativo da tangerineira 'Poncã'. Nesse contexto, adotou-se o delineamento estatístico em blocos casualizados, em parcelas subdivididas, com duas repetições, na instalação do ensaio. Os dois tratamentos de -0,03 e -0,05 MPa, como potenciais mínimos da água no solo, constituíram as parcelas e as quatro doses de paclobutrazol: 0; 4; 8 e 12 g por planta, nas subparcelas. No segundo ano de pesquisa, foram mantidas as mesmas parcelas e foram aplicadas nas plantas das subparcelas as doses de 0; 500; 1000 e 2000 mg l-1 de paclobutrazol, via foliar. Cada parcela foi constituída de 16 plantas, sendo oito destinadas à avaliação. Utilizou-se, em ambas as combinações, de um tratamento sem irrigação (-0,07 MPa) e sem aplicação de paclobutrazol, como testemunha. Foram avaliados parâmetros, como a altura, diâmetro médio, volume e área de projeção da copa e condutância estomática para caracterizar a resposta das plantas aos tratamentos empregados. Concluiu-se que a aplicação do paclobutrazol e a variação do potencial da água no solo não proporcionaram a indução do florescimento fora de época das tangerineiras, e que os níveis de paclobutrazol influenciaram no desenvolvimento das plantas.

PACLOBUTRAZOL RESIDUES IN ‘TOMMY ATKINS’ MANGO FRUITS (Mangifera indica L.)

Mexico is the world´s most important mango exporting country. Approximately 165,000 tons of mangos are exported every year. About 25 % of these exportations belong to the Tommy Atkins cultivar. Due to the fact that the price of mango depends on supply and demand, an early harvest can double or even triple its price. The ammonium and/or potassium nitrates have been used successfully to promote early flowering of several mango cultivars, but there is no success with the Tommy Atkins cultivar. Paclobutrazol (PBZ) has been applied as a soil drench, and has promoted early flowering in the Tommy Atkins cultivar for about 40 days. However, the United States has established a set or restrictions to use this substance due to its high persistence in soil, and because it has been identified as a possible cause of irrigation water pollutant, that could have tralocation in to the fruits. These facts may reduce this fruit exportation to the United States, which produces an income of 40 million dollars per year to Mexico. This research was established with the purpose of determining if PBZ’s residues affect the ‘Tommy Atkins’ mango fruits harvested from trees treated with this plant growth retardant. Commercial ‘Tommy Atkins’ orchards treated with PBZ during 1996, 1997 or during both years were sampled from the 1998’s mangos production season in the states of Michoacán and Colima. PBZ residues were identified by gas chromatography. No PBZ residues were detected when the treatment was applied for a year. When the treatment was applied during two consecutive years, very low levels of PBZ were detected (levels below the detection level).

Physiological persistence of paclobutrazol on the ‘Tommy Atkins’ mango (Mangifera indicaL.) under rainfed conditions

SummaryTo investigate the feasibility of using paclobutrazol (PBZ) to control chemically mango tree size under rainfed conditions, the physiological persistence of soil applied PBZ on the vegetative growth, flowering behaviour, nutritional status, fruit set and quality of ‘Tommy Atkins’ mango was assessed for three consecutive years. A single application of PBZ (0, 2.5, 5,10,15, 20, and 40 g per tree) was made after harvest in June, 1990. Each dosage was dissolved in 2 1 of water and applied in a 15 cm depth trench at 1.5 m around the tree. Shoot length was significantly reduced only with 10 g PBZ per tree and greater concentrations. PBZ at 20 and 40 g per tree drastically reduced vegetative growth for a year after treatment. The effect of 10 g PBZ per tree on shoot growth was modest and lasted one year. With the exception of 40 g PBZ per tree, the effect of any level of PBZ on shoot length disappeared by year three. Increases in PBZ levels increased the earliness of flowering from 16 d (2.5 g PBZ per tree) to 40 d (40 g PBZ per tree) in the first year. For the second year after treatment, the effect of PBZ on time to flowering started to decline and, with the exception of 15 and 40 g PBZ per tree, earliness of flowering disappeared by year three after treatment. PBZ levels from 2.5 to 20 g per tree did not affect the number of mature fruit per m2 of canopy during the three experimental years. PBZ at 40 g per tree resulted in the lowest production of mature fruits for the first two years after application. However, for the third year this treatment produced most mature fruit per m2 of canopy. All PBZ rates decreased average fruit weight, but, the smallest fruits were produced with 15, 20 and 40 g PBZ per tree. Total soluble solids of fruit juice were not affected at low PBZ-rates (2.5 and 5 g per tree), but they were significantly higher with 10 g PBZ per tree and greater concentrations. PBZ at 10 g per tree and above drastically reduced leaf P and Ca content. A similar reduction was found for Mg with levels of 15 g PBZ per tree and above. No significant changes were detected in the leaf content of N and K. The use of 10 g PBZ per tree may have a dual effect, as it may reduce tree size and induce early flowering. To keep this effect, we speculate that under rainfed conditions, a single application of 10 g PBZ per tree should be followed by a reapplication with 10 or 5 g per tree every two years.

Effect of paclobutrazol on growth, chloroplast pigments and sterol biosynthesis of maize ( Zea mays L.)

Growth, chlorophyll, carotenoid and sterol biosynthesis in maize seedlings as influenced by soil drenches of 30, 60 and 90 μM paclobutrazol were studied. The growth regulator delayed seedling emergence and retarded vegetative growth, but increased the dry matter percentage. However, the fresh and dry weight per shoot remained lower in paclobutrazol treated seedlings than in control seedlings. The chloroplast pigments determined per unit fresh or dry weight were not significantly affected by either levels of paclobutrazol, although the treated seedlings appeared more green than the control seedlings. Both chlorophyll and carotenoid concents per leaf were decreased but the chlorophyll concentration per unit leaf area was enhanced by paclobutrazol. This was due to the concentration of the decreased amount of chlorophyll into much smaller leaf area, and indeed the biosynthesis of chloroplast pigments was unaffected by paclobutrazol. Paclobutrazol affected the 14-demethylation and second alkylation reactions in phytosterol biosynthesis but not enough to be phytotoxic.

Effect of gibberellin biosynthesis inhibitors on shoot regeneration from hypocotyl explants of Albizzia julibrissin

Hypocotyl explants of Albizzia julibrissin were placed on Gamborg's B5 medium supplemented with various levels of paclobutrazol, uniconazole, prohexadione calcium, or GA3. Callus formation was evident within one week after placement of the explants on the culture media. Green nodule-like structures protruded from the distal end of the explants within 10 days and developed into shoots within a month. These shoots readily formed adventitious roots when placed on fresh culture medium. All three of the gibberellin biosynthesis inhibitors increased shoot formation compared to the control. The number of shoots per explants was increased 107, 79, and 168% by 0.3-0.4 μM paclobutrazol, uniconazole, and prohexadione calcium, respectively. In contrast to the gibberellin biosynthesis inhibitors, GA3 decreased shoot formation. These results indicate that modification of gibberellin status can have a strong impact on the number of shoots formed.

NM and Paclobutrazol Control Grapevine Suckers: Vine Performance and Fruit Tissue Residues

`Okanagan Riesling' (Vitis spp. parentage unknown) vine trunks treated in 1984 with three levels of NM (0, 10,000, and 20,000 mg·liter-1) and three levels of paclobutrazol (PB; 0, 250, and 500 mg·liter-1, in white latex paint were subjected to a reapplication in June 1987 at the same rates of NAA and at 0, 1000, and 2000 mg PB/liter. Linear reductions in suckers per vine were observed with increasing NAA concentration but not PB. Yield and clusters per vine were reduced by PB in the season following retreatment (1988), while berry weight was increased by NAA in 1987. Titratable acidity was increased by NAA in 1988, and pH was highest that season with PB at 1000 mg·liter-1. No PB was detected in fruit tissue in 1987, but NAA levels of 2.4 and 2.0 μg·kg-1 were detected in clusters sampled from the 10,000- and 20,000-mg·liter -1 treatments, respectively. Chemical names used: l-naphthaleneacetic acid (NAA); β-1[(4-chlorophenyl)methy]-α-1 (l,l-dimethylethyl)-1H-l,2,4-triazole-l-ethanol (paclobutrazol).

Influence of paclobutrazol on mineral element content of rice seedlings

Abstract Rice seedlings (Oryza sativa cv. Te Qin No. 1) were hydroponically grown in Espino's solution containing various levels of paclobutrazol introduced into the solution at the three‐leaf stage. After the 15th day of treatment, several mineral elements were determined to evaluate the effect of paclobutazol on mineral uptake. In the root, paclobutrazol increased the concentration (on a dry weight basis) of N, P, K, and Cu, decreased Ca and Fe, and did not affect Mg. In the shoot, paclobutrazol enhanced N, P, Ca, and Cu concentration, but decreased Mg, and did not influence K And Fe. In the whole seedling, P, Ca, and Cu concentrations were increased, but N, K, Mg, and Fe were not changed. The total content of mineral elements (on per plant basis) in the shoot and whole seedlings was decreased by paclobutrazol treatment. Fe in the root also decreased. Based on the results mentioned above, paclobutrazol, in general, does not increase the total content of mineral elements in the plant; however, if element...

SUPPRESSING RHIZOME GROWTH AND TUBER FORMATION IN PURPLE NUTSEDGE BY PACLOBUTRAZOL

Purple nutsedge is a difficult weed to eradicate due to extensive underground growth. One eradication strategy is to inhibit tuber formation for preventing reproduction, In developing this strategy, soil applications of paclobutrazol (PA) were conducted to suppress rhizome and tuber development in Hawaii. Factors examined were 4 PA levels at 0, 0.5, 2 and 8 mg ai·liter-1 (medium) and 4 application types: a) soil drench, fresh tuber, b) soil incorporation, fresh tuber, c) soil drench, stored tuber for 1 month at 4C, and d) drench to a synthetic medium (vermiculite: perlite = 2: 1 by volume), fresh tuber. Treatment design was 4×4 factorial with 5 replications, and experimental unit was a tuber planted 2 cm deep in a 1-liter plastic container. Two months after planting tuber numbers and rhizome lengths were recorded and analyzed for regression and orthogonal comparisons. Control means were 11.1 tubers and 1178 mm total rhizome length. PA reduced both measurements as no tuber was formed at 2 or 8 mg ai·liter-1 and total rhizome lengths were limited to 8 and 3 mm, respectively. PA was less effective in the synthetic medium than in the soil, while application methods and tuber storage did not result in significant differences.

Translocation of Triazole Growth Retardants in Plant Tissues

Abstract Translocation patterns of the triazole plant growth retardants paclobutrazol, triapenthenol, and BAS111 were found to be similar when applied as a trunk paint, soil drench, or in hydroponic systems. Chemical degradation studies indicate that the greatest percentage of parent compound is translocated to roots and mature leaves following soil drench and hydroponic treatments. Generally, residue levels of BAS111 were significantly lower than those of paclobutrazol and triapenthenol. Data from trunk paint applications indicate triapenthenol and BAS111, even at concentrations 5 times greater than paclobutrazol, are not as effective in controlling shoot growth. Significant negative correlations were found between shoot growth and foliar residue levels of paclobutrazol and triapenthenol 13 weeks after trunk paint application. Chemical names used: (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pentan-3-ol (paclobutrazol); (E)-(RS)-1-cyclohexyl-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)-pent-1-en-3-ol (triapenthenol); 1-phenoxy-5,5-dimethyl-3-(1,2,4-triazol-1-yl)-hexan-5-ol] (BAS111); trimethylonylpolyethoxyethanol (WK surfactant).

Transitory growth control of apple seedlings with less persistent triazole derivatives

Paclobutrazol, triapenthenol (RSW0411), and BAS111 were applied to 4-week-old Delicious apple seedlings (Malus domestica Borkh.) as a root drench at 0.1, 1.0, and 10.0 mg per plant. Paclobutrazol eliminated shoot extension growth for 8 weeks at all three rates. RSW0411 controlled shoot elongation only at the highest rate. BAS111 produced the widest response, with shoot growth ranging from 38% to 93% of controls for the highest and lowest rates, respectively. Generally, leaf area decreased and leaf density increased with increasing rates of all chemicals. Root weight of plants treated with paclobutrazol nearly doubled but increased only slightly with RSW0411 and BAS111. Chemical analysis of the leaf tissue 8 weeks after treatment showed paclobutrazol levels highest, followed by RSW0411 and BAS111.

Chemical Growth Retardants Increase Seed Yield in Apple Trees

Abstract In two experiments the effects of trunk drenches with two gibberellin biosynthesis inhibitors on vegetative growth, seed yield and quality of ‘Delicious’ and ‘Golden Delicious’ apple trees were studied. In the first experiment trunk drenches of either paclobutrazol or uniconizole were applied to ‘Golden Delicious’ apple trees in spring 1984. Both chemicals significantly reduced shoot length in 1985 and 1986. In 1986, fruit number tended to be higher in treated trees, but was less than untreated trees in 1985 and 1984. The estimated number of sound seeds produced in 1986 on treated trees was increased. Neither chemical significantly affected seed quality or seedling growth. In a second similar experiment paclobutrazol, applied as a trunk drench in spring 1984 at rates of 2, 4 or 8 g active ingredient (ai)/tree, significantly reduced shoot growth in 1985 and 1986. The number of sound seed/tree was significantly increased in 1986 at all paclobutrazol levels due to an increase in the number of fruit/tree. Paclobutrazol application had no effect on seed quality, rate of germination, final percent germination, or on seedling growth. Potentially, both compounds could be used to control vegetative growth without affecting seed yield or quality in deciduous seed orchards.

Response of ‘Tifblue’ Rabbiteye Blueberry to Soil-applied Paclobutrazol

Abstract Bud development in ‘Tifblue’ rabbiteye blueberry (Vaccinium ashei Reade) was reduced with increasing levels of soil-applied paclobutrazol (PB). Flowering was delayed from 10 to 15 days on plants receiving ≥3 g a.i. PB. This effect still existed 2 years after treatment. Rates of ≤2 g per plant did not influence leaf area. Floral or vegetative bud development, photosynthesis, transpiration, or fruit size when measured 1 year after treatment, but fruit yields were inversely correlated to PB levels. Two years after application, ≤2 g rates had not influenced total plant growth. Stems arising from mature canes were reduced by ≥ 0.5 g PB, but length of juvenile canes was increased by rates up to 2 g PB. Paclobutrazol applications had no influence on leaf content of N, P, Ca, Mg, Fe, or Cu. Only the highest level resulted in increased leaf levels of K and Zn, but Mn leaf content was increased by all levels of PB. In general, rates of soil-applied PB which reduced vegetative growth also reduced fruit yield. Chemical name used: β [(4-chlorophenyl)methyl]-α-(1,1 dimethylethyl)-1H-1,2,4-triazole-l-ethanol (paclobutrazol).

Inhibition of Lateral Shoot Growth in Summer-hedged ‘Riesling’ Grapevines by Paclobutrazol

Abstract ‘Riesling’ (Vitis vinifera L., clone 21B Weis) vines under each of two canopy management treatments (nonhedged, hedged) were subjected to two levels of paclobutrazol (PB) (0, 500 mg·liter–1; 750 mg·liter–1 in 1 year)applied as a foliar spray to the upper portion of the canopy. PB reduced growth of lateral shoots, primarily to the uppermost portion of the main shoot, in both hedged and nonhedged vines. Vine size was not reduced by PB application. PB increased °Brix in fruit of hedged vines in 1984 and 1986. No major effects of either factor were observed on yield components, but PB increased berry size in 1986. Chemical name used: β-[(4-chlorophenyl) methyl]-α-(1,1-dimethylethyl)-1-H-1,2,4-triazole-1-ethanol (paclobutrazol).

Extraction, Purification, and Quantitation of Paclobutrazol from Fruit Tree Tissues

Abstract β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1 H-1,2,4-triazole-1-ethanol (paclobutrazol) is one of a new class of plant growth regulators that affect both vegetative and reproductive components of fruit tree growth (1-3). The movement and fate of absorbed paclobutrazol must be established to better understand its persistence and mode of action. Accordingly, we have developed an analytical method for quantifying low levels of paclobutrazol extracted from plant tissue.

Influence of Paclobutrazol on Selected Growth and Chemical Characteristics of Young Pecan Seedlings

Abstract Soil drench applications of paclobutrazol (0, 0.5, 1, 2, 4, 8, 16, and 32 mg a.i·pot-1) to greenhouse grown pecan seedlings reduced plant height, plant dry weight, organ dry weight, in ter node length, leaf thickness, leaf area, and chlorophyll content. Carbohydrate levels (mg·g dry weight-1 and mg·g plant-1) in treated plants increased. Total plant carbohydrate levels were unchanged at levels ≤ 2m g a.i.·pot-1, but plants of reduced size showed increased levels of carbohydrates per mg of tissue. Seedlings treated with high levels of paclobutrazol had a slight tendency for increased net photosynthesis.