Growth retarding effects of paclobutrazol and RSW 0411 on Granny Smith and Fuji apple trees

The growth retardants paclobutrazol (β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol) and RSW 0411 (β-(cyclohexyl methylene)-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol) were tested on two-year-old trees of Granny Smith and Fuji apple. RSW 0411 at 100 mg/L did not cause any growth reduction in Granny Smith, while 500 and 1000 mg/L significantly reduced growth below that of the control between 27 and 40 days after application. Paclobutrazol at 100 mg/L had significantly reduced shoot growth between 27 and 55 days after application, and 1000 mg/L reduced shoot growth between 27 and 82 days after application. By 100 days after application, there were no longer differences between treatments. Shoot growth on Fuji trees was reduced below that of the control as follows: between 14 and 27 days following a single application of 500 mg/L RSW 0411; between 27 and 55 days following two applications; between 14 and 72 days following three applications; and between 14 and 82 days following four applications. Treatments were applied 14 days apart. Paclobutrazol was a more active growth retardant than RSW 0411 at the same rate, and the growth-retarding effects of RSW 0411 were short-lived.     

Growth and biomass production in potato grown in the hot tropics as influenced by paclobutrazol

Two similar field trials were carried out during 2003 in a hot tropical region of eastern Ethiopia to investigate the effect of leaf and soil applied paclobutrazol on the growth, dry matter production and assimilate partitioning in potato. A month after planting paclobutrazol was applied as a foliar spray or soil drench at rates of 0, 2, 3, and 4 kg a.i. paclobutrazol ha^–1. Plants were sampled during treatment application and subsequently 2, 4, 6 and 8 weeks after treatment application. The data was analyzed using standard growth analyses techniques. None of the growth parameters studied was affected by the method of paclobutrazol application. Paclobutrazol decreased leaf area index, crop growth rate, and total biomass production, and increased specific leaf weight, tuber growth rate, net assimilation rate, and partitioning coefficient of potato. At all harvesting stages, paclobutrazol reduced the partitioning of assimilate to the leaves, stems, and roots and stolons and increased allocation to the tubers. Although paclobutrazol decreased the total biomass production it improved tuber yield by partitioning more assimilates to the tubers. Paclobutrazol improved the productivity of potato under tropical conditions by redirecting assimilate allocation to the tubers.     

Growth and photosynthesis of sweet orange plants treated with paclobutrazol

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan3-ol], formulated as GFU 265, applied at 100, 250, and 500 mg plant^–1 to the soil of container-grown sweet orange [Citrus sinensis (L.) Osbeck cv. Valencia], suppressed plant weight, stem height, leaf size, and total leaf area. At the 500-mg dosage, total plant dry weight was reduced by 61%, stem height by 74%, and both leaf biomass and area by 80%, as compared to control plants. All paclobutrazol dosages induced fibrous root thickening and increased their soluble sugar and starch content. Fresh root biomass was 14 to 40% higher and root:shoot ratios were increased three- to sixfold for treated plants. Paclobutrazol applications of 250 and 500 mg plant^–1 reduced leaf photosynthetic rate, ribulose bisphosphate carboxylase activity, total nonstructural carbohydrates, and dark respiration 70 to 80% of the control plants. Reductions of leaf photosynthetic rate, carboxylase activity, and photosynthate by paclobutrazol contributed to biomass reduction in treated sweet orange.Mention of a trademark, warranty, proprietary product, or vendor does not constitute a guarantee by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable.     

Response of potato grown under non-inductive condition paclobutrazol: shoot growth, chlorophyll content, net photosynthesis, assimilate partitioning, tuber yield, quality, and dormancy

The effect of foliar and soil applied paclobutrazol on potato were examined under non-inductive condition in a greenhouse. Single stemmed plants of the cultivar BP1 were grown at 35(±2)/20(±2) °C day/night temperatures, relative humidity of 58%, and a 16 h photoperiod. Twenty-eight days after transplanting paclobutrazol was applied as a foliar spray or soil drench at rates of 0, 45.0, 67.5, and 90.0 mg active ingredient paclobutrazol per plant. Regardless of the method of application paclobutrazol increased chlorophyll a and b contents of the leaf tissue, delayed physiological maturity, and increased tuber fresh mass, dry matter content, specific gravity, dormancy period of the tubers. Paclobutrazol reduced the number of tubers per plant. A significant interaction between rates and methods of paclobutrazol application were observed with respect to plant height and tuber crude protein content. Foliar application gave a higher rate of net photosynthesis than the soil drench. Paclobutrazol significantly reduced total leaf area and increased assimilate partitioning to the tubers. The study clearly showed that paclobutrazol is effective to suppress excessive vegetative growth, favor assimilation to the tubers, increase tuber yield, improve tuber quality and extend tuber dormancy of potato grown in high temperatures and long photoperiods.     

Growth Responses and Allocation of Assimilates of Rice Seedlings by Paclobutrazol and Gibberellin Treatment

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)methyl-4,4-dimethyl-2-(1h-1,2,4-trizol-1-yl)penten-3-ol] effectively decreased vegetative growth of rice (Oryza sativa L.) seedlings and increased the chlorophyll content. The number of veins in a leaf, the calculated number of stomata per leaf, and the length of guard cells were not altered by the paclobutrazol treatment, suggesting an effect on cell elongation. The allocation pattern of carbohydrates was changed by either gibberellin (GA) or paclobutrazol treatment. GA₃ induced more shoot growth and less accumulation of starch than the control and paclobutrazol-treated seedlings. Photosynthetic ability was not affected by either paclobutrazol or GA₃ treatment. Paclobutrazol-treated plants allocated a smaller amount of photosynthates for vegetative shoot growth and stored more as starch in the crowns than the control and GA₃-treated plants. The same starch degrading activity in the crown tissue of paclobutrazol-treated seedlings as in control plants suggests that the accumulated starch is utilized in a normal activity for growth including leaf emergence, tiller formation, and root production, resulting in improved seedling quality. Received May 30, 1996; accepted December 10, 1996     

Effect of paclobutrazol on cell wall polysaccharide composition of the apple tree

The effect of paclobutrazol, a gibberellin biosynthesis inhibitor, on cell wall carbohydrate composition of apple shoots was determined. Inhibition of apple shoot extension corresponded to a change in wall composition. Paclobutrazol did not inhibit shoot growth during the first year (1983) after the treatment. There was also no significant difference in cell wall carbohydrate composition between control and paclobutrazol treated shoots. In the second year (1984), however, paclobutrazol altered the composition of cell wall polysaccharides and inhibited shoot extension. Paclobutrazol treatment increased rhamnose, arabinose and galacturonic acid but decreased cellulose. The ratio of xylem to phloem was also reduced by paclobutrazol treatment.     

Uptake and translocation of paclobutrazol by shoots of M.26 apple rootstock

When ¹⁴C-paclobutrazol, a gibberellin synthesis inhibitor, was applied to different parts of actively-growing M.26 apple rootstock shoots it was translocated acropetally when applied to the young stem and, to a lesser extent, from the youngest unrolled leaf. Paclobutrazol was not translocated out of leaf laminae, shoot tips or from one-year-old wood but translocation occurred out of a treated petiole into the attached leaf. No basipetal translocation was detected. This translocation pattern suggested movement through the xylem.Localised application of paclobutrazol caused a reduction in shoot extension and leaf production when the young stem or shoot tip were treated; the effect decreased as older parts of the stem were treated. Treatment of laminae or petioles had only a slight effect on shoot extension and treatment of one-year-old wood was ineffective. Combined treatment of the shoot tip plus young stem was similar in effect to treatment of the complete shoot.It is suggested that paclobutrazol exerts its effects on shoot growth by inhibiting gibberellin biosynthesis in the shoot tip and the expanding leaves.The findings contribute to an understanding of the requirements for efficient orchard application of foliar sprays of paclobutrazol.     

Precocious gladiolus corm formation in liquid shake cultures

Conditions were defined for precocious differentiation and improved growth of corms at the base of gladiolus shoots. Shoots were derived from explants cultured on agar solidified media, and corm regeneration was obtained in subsequent liquid shake cultures. Benzyladenine (BA), at 10^-7 M, was found to have a stimulating effect mainly when provided to the shoots prior to manifestation of corm growth. Paclobutrazol and sucrose promoted corm formation when supplemented to the liquid media. Paclobutrazol, at 10 mg l^-1, shifted assimilate allocation towards the growing corm. A differential promotion of corm development by sucrose was not observed, and the concentration of sucrose at which the sugar demand for maximal shoot and corm growth is satisfied (60 g l^-1) was unaltered by the presence of paclobutrazol. The rate of corm growth on shoots cultured in a liquid medium supplemented with paclobutrazol and a saturating sucrose concentration, was a function of the length of the shoot's leaf blades, and was similar in light and in dark.     

Uptake,translocation, and metabolite partitioning of14C-labeled metribuzin in plant growth-regulated soybean (Glycine max)

Plant growth regulator (PGR) application decreased uptake of 10^–6 M¹⁴C-labeled metribuzin (4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one) into leaf interveinal areas of 21-day-old soybean seedlings. BAS 140 810, (N-allyl-N-2-(2,4,6-trichlorophenoxy)ethyl-piperidinium-bromide), as a seed treatment or 10^–6 M triapenthenol or RSW 0411 (B-(cyclohexalmethylene)-gamma-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol) in nutrient solution slowed interveinal unloading of metribuzin and altered metabolite pools. Stems and roots of PGR-treated plants exhibited significantly greater water-soluble metabolite pools than untreated controls. TLC metabolite identification indicated an increase in metribuzin conjugates. This may contribute to the mode of action involved in the apparent safening mechanism. Furthermore, floating leaf disk studies with metribuzin showed plant growth regulation figured prominently in safening against the cessation of oxygen evolution.     

Effect of paclobutrazol on accumulation of organic acids and total phenols in apple wood

Apple trees (Malus domestica Borkh Spartan grafted on MM 106 rootstock) planted in 1976 in an orchard at Beltsville, Maryland, were treated with paclobutrazol (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-1,2,4-triazol-1-yl-pentan-3-ol) using a foliage spray in 1982 and by trunk banding in 1983. Paclobutrazol did not inhibit shoot growth in 1983; however, shoot growth was significantly retarded in 1984. Increases in organic acids, including succinic, malic, citric, and quinic, and also in total phenols, occurred in wood produced in 1983 on paclobutrazol-treated trees when growth was not inhibited and in wood produced in 1984 when growth was inhibited. The organic acid content of both paclobutrazol-treated and untreated wood tended to decrease from the winter dormant period through growth resumption in the spring. However, the content of total phenols remained nearly the same throughout this sampling period.Mention of a trademark, proprietary product or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Effects of mixtalol and paclobutrazol on photosynthesis and yield of rape (Brassica napus)

Photosynthetic and yield effects of paclobutrazol and mixtalol sprayed, respectively, on rape at the three-leaf stage and shoot or anthesis stages were examined. They significantly increased chlorophyll content and photosynthetic rates, prolonged leaf longevity, and increased green pod area. Paclobutrazol-treated plants were shorter, more branched, and produced more seeds. Foliar sprays of mixtalol increased podding percentage, pods per plant, and seeds per pod. A high seed yield of 1809.0 kg/ha was obtained with mixtalol sprayed at anthesis, while significant yields were also achieved with treatments of mixtalol at the shoot stage and paclobutrazol at the three-leaf stage. The photosynthetic and yield effects of mixtalol or paclobutrazol were reduced when both growth regulators were applied together, and this led to yield reductions. No adverse effects from mixtalol or paclobutrazol were observed on seed oil content, erucic acid, and glucosinolate content. The total rape oil production with mixtalol sprayed at anthesis and shoot stages and paclobutrazol at the three-leaf stage increased significantly by 20.9%, 14.4%, and 13.4%, respectively, over the controls.     

Influence of paclobutrazol in the soil on growth,nutrient elements in the leaves,and flood/freeze tolerance of citrus rootstock seedlings

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3ol] was applied to soil at 0, 100, or 250 mg/3.78-liter pot containing seedlings of Swingle citrumelo, Carrizo citrange, Cleopatra mandarin, sour orange, rough lemon, and Sun Chu Sha. All cultivars were sensitive to paclobutrazol, which caused a proliferation of shorter/thicker roots, and top growth showed shorter internodes and lower dry weight. Induced changes resulted in greater root/shoot ratios, and paclobutrazol treatments showed higher concentrations of nitrogen, calcium, boron, iron, and manganese in the leaves of different cultivars. Paclobutrazol-treated seedlings did not show a greater ability to tolerate flooded soil for 60 continuous days under greenhouse conditions nor survive-6.7°C controlled freeze tests. Paclobutrazol is a potentially useful plant growth regulator to dwarf citrus, but it apparently is not a strong candidate for increasing flooding and freezing tolerance in citrus rootstock seedlings.Abbreviations PPFD photosynthetic photon flux density - ANOVA analysis of variance     

Relative efficacy of paclobutrazol, propiconazole and tetraconazole as stress protectants in wheat seedlings

The stress protective effects of triazoles including paclobutrazol, a plant growth regulator, and two fungicides, propiconazole and tetraconazole, are compared. Wheat (Triticum aestivum L. cv Katepwa) seeds were imbibed for 18 h in distilled water (Ck) or in aqueous solutions of each triazole (50 mg L-1). Seeds were then air dried, planted in sectioned plastic flats and grown in a greenhouse. After 10 days, one set of seedlings were allowed to continue growing under optimal conditions while additional sets were exposed to various stresses including high temperatures, drought and spray with the herbicide paraquat. Compared to wheat leaves from plants grown under optimal conditions, heat stress decreased shoot fresh weight, fluorescence values and chlorophyll levels. It also increased ion leakage. All symptoms of damage were alleviated by the triazoles, with paclobutrazol being the most potent. Similar trends were found under acute drought conditions, where seedlings treated with paclobutrazol had the highest percent survival and the most shoot regrowth upon rewatering. Paclobutrazol was also the best triazole in protecting wheat leaves from damage caused by paraquat, a free radical generator. It is concluded that while all the triazoles have the potential to be stress protectants, paclobutrazol was consistently the most effective.     

Response of Eucalyptus nitens seedlings to gibberellin biosynthesis inhibitors

The plant growth regulators (PGRs) paclobutrazol, chlormequat chloride and prohexadione where applied to 11 month old seedling of Eucalyptus nitens to examine their relative effects on precocious flowering, growth and levels of GA20 and GA1 in the shoot apex. Paclobutrazol was most effective in reducing growth and levels of GA20 and GA1 in the seedlings followed by chlormequat chloride with prohexadione being least effective. Paclobutrazol and chlormequat chloride reduced both GA20 and GA1 levels by similar degrees, but prohexadione reduced GA1 levels considerably more than GA20 levels. None of these PGRs was effective in promoting precocious flowering. This suggests that there is an extra level of reproductive control operating in juveniles of this species compared to those of the closely related species E. globulus previously found to flower precociously in response to similar paclobutrazol treatments.     

Response to paclobutrazol of symbiotic mycorrhizal fungi and dropper (tuber stalk) formation of host orchid seedlings

The effects of the triazole compound paclobutrazol on the mycorrhizalfungi and production of droppers (tuber stalks) in three species of terrestrialorchids of southwestern Australia were investigated. Seedlings ofDiuris laxiflora Lindley (bee orchid), Microtismedia R. Br. (common mignonette orchid), and Pterostylissanguinea D. Jones & M. Clements (dark banded greenhood orchid)were cultured symbiotically with specific mycorrhizal fungi invitro. The mycorrhizal fungi of the study species were grown on mediacontaining paclobutrazol at 0, 1.7, 3.4, 10.2, or 17.0 M(corresponding to 0, 0.5, 1.0, 3.0, or 5.0 mgL^–1). Paclobutrazol at all concentrations evaluateddecreased the growth rates of the mycorrhizal fungi of M.media and P. sanguinea below that of thecontrol. However, paclobutrazol did not adversely affect the growth of themycorrhizal fungus of D. laxiflora, and low concentrations(1.7 or 3.4 M) stimulated the growth of this fungus. Symbiotic seedlings of the study species were exposed to paclobutrazolat 0, 1.7, 3.4, 10.2, or 17.0 M. Paclobutrazol at allconcentrations evaluated increased dropper (tuber stalk) production inD. laxiflora, but had no effect on M.media and P. sanguinea.This suggests that, for species in which paclobutrazol has no fungicidaleffect on mycorrhizal fungi, it has the potential to stimulate early andefficient tuberization of symbiotic orchid seedlings.     

In vitro responses and acclimatization of Prunus serotina with paclobutrazol

Paclobutrazol (PBZ), a triazole growth retardant known to improve tolerance of various species to stress, was incorporated into the in vitro rooting medium of Prunus serotina var. virens at rates of 0.00, 0.15, 0.30, and 0.60 mg/L with and without 1.0 mg/L indolebutyric acid (IBA). PBZ significantly reduced shoot growth in vitro but increased/improved the quality and coloration. The percentage of water loss from detached leaves of in vitro plantlets was significantly reduced by PBZ and IBA. At 4 weeks after transfer to the greenhouse, survival was significantly improved by PBZ, IBA, and the combination. Incorporation of PBZ in vitro better enables Prunus serotina plantlets to withstand the stresses associated with acclimatization.     

Mycorrhizal fungi enhancement of growth and gas exchange of micropropagated guava plantlets (Psidium guajava L.) during ex vitro acclimatization and plant establishment

Psidium guajava L.) plantlets was determined during acclimatization and plant establishment. Guava plantlets were asexually propagated through tissue culture and grown in a glasshouse for 18 weeks. Half of the plantlets were inoculated with a mixed endomycorrhiza isolate from Mexico, ZAC-19, containing Glomus diaphanum, G. albidum and G. claroides. Plantlets were fertilized with modified Long Ashton nutrient solution that supplied 11 μg P ml⁻¹. Gas exchange measurements were taken at 2, 4, 8, and 18 weeks after inoculation using a portable photosynthesis system. All micropropagated guava plantlets survived transplant shock. After 6 weeks, mycorrhizal plantlets had greater shoot growth rates and leaf production than non-mycorrhizal plantlets. This also corresponded with increased photosynthetic rates and stomatal conductance of mycorrhizal plants. By 18 weeks, mycorrhizal plantlets had greater shoot length, leaf area, leaf, stem, and root dry mass. However, gas exchange was comparable among treatments, in part because the container size was restricting growth of the larger mycorrhizal plantlets. Non-mycorrhizal plantlets had greater leaf area ratios and specific leaf areas than mycorrhizal plantlets. Increased leaf tissue mineral levels of P, Mg, Cu, and Mo also occurred with mycorrhizal plantlets. Roots of inoculated guava plantlets were heavily colonized with arbuscules, vesicles and endospores. Guava plantlets were highly mycotrophic with a mycorrhizal dependency index of 103%. Accepted: 27 December 1999     

Effects of applied gibberellic acid and paclobutrazol on leaf expansion and biomass allocation in two Aegilops species with contrasting leaf elongation rates

The role of gibberellin (GA) in leaf elongation has long been known, however, its involvement in whole shoot growth and biomass allocation is much less clear. We studied the effects of exogenously supplied GA₃ and paclobutrazol, an inhibitor of GA biosynthesis, on these processes in Aegilops caudata and Aegilops tauschii , species with contrasting leaf growth characteristics. In both species, addition of GA₃ increased leaf elongation rate (LER) through its promoting effect on both cell size and cell number, while paclobutrazol decreased it. Similarly, GA₃ increased biomass allocation to the leaves, mainly leaf sheaths, at the cost of allocation to the roots, whereas paclobutrazol had the opposite effect in both species. Despite the increase in LER and biomass allocation to the shoot upon GA₃ application, the relative growth rate (RGR) remained constant. Specific leaf area (SLA) was only temporarily affected by GA₃ addition. Our results show that the inherent differences in LER and biomass allocation between the slow-elongating A. caudata and the fast-elongating A. tauschii are considerably reduced by the exogenous supply of GA₃ to the slow-elongating species, or paclobutrazol to the fast-elongating one. This suggests a role for gibberellins in explaining inherent differences in leaf area expansion and biomass allocation between the two species in this study.     

多效唑对不同立地条件下黄荆生长及生理特征的影响

该试验以绿化卷材为基质材料,对沙场、渣场和混凝土屋面3种立地条件下生长的黄荆进行不同浓度(0、100、200、300、400mg·L~(-1))多效唑处理,研究根施多效唑对黄荆生长和生理特征的影响以及不同立地环境的应用差异。结果显示:(1)随多效唑浓度升高,3种立地类型黄荆株高和生物量呈降低趋势,冠幅、基径、叶面积、根幅、主根长和主根径呈减小趋势,叶片长宽比和根冠比表现出增大的趋势;多效唑处理使黄荆叶片相对含水量、叶绿素含量、可溶性糖和可溶性蛋白含量增加,使丙二醛含量下降。(2)不同立地条件下黄荆对多效唑处理的表现具有一定差异,隶属函数法综合评价显示,对沙场、渣场和屋面3种立地类型的黄荆生长调控效果最佳的多效唑浓度分别为400mg·L~(-1)、300mg·L~(-1)、100mg·L~(-1)。(3)当多效唑浓度在渣场和屋面分别为400、300mg·L~(-1)时,黄荆叶片开始受到伤害,对多效唑的耐受阈值表现为沙场渣场屋面。研究认为,多效唑可有效调控黄荆的形态和生物量分配,增强细胞渗透调节和抗氧化损伤能力,从而提高黄荆的抗逆性和环境适应性,但在应用时应考虑不同立地背景的差异,因地制宜地选择使用浓度和用量,使其更好地应用于人工植被恢复与建设。     

Effect of the Rht3 dwarfing gene on dynamics of cell extension in wheat leaves, and its modification by gibberellic acid and paclobutrazol

The second leaf of wheat was used as a model system to examinethe effects of the Rht3 dwarfing gene on leaf growth. Comparedto the rht3 wild type, the Rht3allele decreased final leaf length,surface area and dry mass by reducing the maximum growth rates,but without affecting growth duration. Gibberellic acid (GA₃)increased final leaf length and maximum growth rate in the rht3wild type, but was without effect on the Rht3 mutant, whichis generally regarded as being non-responsive to gibberellin(GA). Paclobutrazol, an inhibitor of GA biosynthesis, decreasedfinal leaf length and maximum growth rate in the rht3 wild typeto values similar to those in the untreated Rht3 mutant. NeitherGA₃ nor paclobutrazol affected the duration of leaf growth.The decrease in leaf length was produced by reduction of celllength rather than cell number. The maximum relative elementalgrowth rate (REGR) for cell extension was essentially the samein all treatments, as was the time between the cells leavingthe meristem and achieving maximum extension rate. The differencesbetween the genotypes and treatments were all almost entirelydue to differences in the time taken from the attainment ofmaximum REGR of cell extension to the cessation of extension.This was reflected in the length of the extension zone, whichwas approximately 6–8 per cent of final leaf length. Theeffects of the Rht3 allele, GA₃ and paclobutrazol all appearto be on the processes which promote the cessation of cell elongation. Key words: Cell extension, gibberellin, leaf growth, Rht3 gene, Triticum, wheat