Foliar Paclobutrazol Application Suppresses Olive Tree Growth While Promoting Fruit Set

In some agricultural practices, application of plant growth regulators is very useful as an efficient means to modulate olive tree vigour to optimize fruit production. However, the physiological mechanisms underlying these effects are still poorly understood. Here, we evaluated the effectiveness of paclobutrazol, chlormequat and prohexadione on the modulation of vegetative growth and fruit set, with a special emphasis on the underlying effects exerted by phytohormones, in one-year-old olive trees (Olea europea cv. Arbosana). Paclobutrazol and chlormequat were tested using both foliar spraying and soil irrigation, while prohexadione was applied by foliar spraying only, and all treatments were compared to a control. Among treatments, paclobutrazol and chlormequat were the most effective in promoting vegetative growth retardation, when applied through foliar spray. Growth retardation by foliar application of paclobutrazol was associated with proline accumulation and reduced gibberellin contents in leaves. Furthermore, hormonal profiling revealed that not only all treatments were effective in reducing the endogenous contents of gibberellins, but also that the entire hormonal profiling was altered upon treatments. It is concluded that (i) various plant growth regulators can be effectively used to control olive tree growth, and (ii) paclobutrazol seems to be more efficient on vegetative growth retardation than the other tested treatments, being foliar application more effective than soil treatment.

     

The effects of lodging and a paclobutrazol — chlormequat chloride mixture on the yield and quality of oilseed rape

The effects of lodging and a plant growth regulator mixture on oilseed rape cv. Ariana were studied in three field experiments. Natural and artificially induced lodging treatments varying in time of imposition and severity were compared to a supported control. A mixture of paclobutrazol and chlormequat chloride was applied either as a spray or as paclobutrazol granules followed immediately by a chlormequat chloride spray.
In 1987, severe lodging treatments reduced yield by up to 52%. Yield penalties varied with the time at which lodging was imposed. Yield was inversely correlated with the ground cover of volunteers growing from shed seed under lodged crops.
In 1988, two experiments showed increased incidence of disease and decreases in seed yield and quality in lodged crops. Yield reductions were related to the severity of lodging. Lodging decreased oil contents and increased glucosinolate levels. PGR treatments reduced lodging and maintained yield at a level not significantly different to a supported control treatment. Oil contents were also similar in seed from PGR treated and control plots. Glucosinolate levels in PGR treated seed were similar to control levels in one experiment and intermediate to those from control and artificially lodged plots in another experiment.
The results are discussed in relation to the use of PGRs to prevent lodging in 'double zero' varieties of oilseed rape, and the potential losses from using ground vehicles to apply pesticides after flowering.     

Epigenetic and physiological effects of gibberellin inhibitors and chemical pruners on the floral transition of azalea

The ability to control the timing of flowering is a key strategy in planning the production of ornamental species such as azaleas; however, it requires a thorough understanding of floral transition. DNA methylation is involved in controlling the functional state of chromatin and gene expression during floral induction pathways in response to environmental and developmental signals. Plant hormone signalling is also known to regulate suites of morphogenic processes in plants and its role in flowering-time control is starting to emerge as a key controlling step. This work investigates if the gibberellin (GA) inhibitors and chemical pinching applied in improvement of azalea flowering alter the dynamics of DNA methylation or the levels of polyamines (PAs), GAs and cytokinins (CKs) during floral transition, and whether these changes could be related to the effects observed on flowering ability. DNA methylation during floral transition and endogenous content of PAs, GAs and CKs were analysed after the application of GA synthesis inhibitors (daminozide, paclobutrazol and chlormequat chloride) and a chemical pruner (fatty acids). The application of GA biosynthesis inhibitors caused alterations in levels of PAs, GAs and CKs and in global DNA methylation levels during floral transition; also, these changes in plant growth regulators and DNA methylation were correlated with flower development. DNA methylation, PA, GA and CK levels can be used as predictive markers of plant floral capacity in azalea.     

Different inhibitors of the gibberellin biosynthesis pathway elicit varied responses during in vitro culture of aspen (<Emphasis Type="Italic">Populus tremula</Emphasis> L.)

Several synthetic plant growth regulators (PGRs), including prohexadione-calcium (ProCa), paclobutrazol (PBZ), and chlormequat chloride (CCC), known for their ability to inhibit gibberellin (GA) biosynthesis, were investigated for their influence on Populus tremula L. (aspen) shoots grown in vitro. Changes in plant growth induced by these inhibitors were compared to the effects of exogenous gibberellins (GA₃ and GA_4/7). All PGRs were added to the nutrient medium at concentrations of either 1 or 5 μM. Stem segments with and without apical buds were excised from in vitro-grown shoot culture, and these explants were incubated either in test tubes or Petri dishes. In the presence of 5 μM ProCa, shoot growth and rooting were inhibited when grown in test tubes, while shoots grown in Petri dishes exhibited strongly enhanced shoot and root growth. PBZ suppressed shoot development both in test tubes and Petri dishes, although 1 μM PBZ promoted adventitious root formation when shoots were grown in test tubes. Five micromolars CCC suppressed shoot and root development in test tubes, but promoted shoot growth in Petri dishes.     

Influence of gibberellin biosynthesis inhibitors on stem elongation and floral initiation on in vitro chicory root explants under dark and light conditions

Root explants of chicory (Cichorium intybus L.) were cultured in vitro under continuous light or darkness. On a standard medium (no plant growth regulators added), flowering-stems were initiated under continuous light while under continuous dark, vegetative-stems were formed. Different types of GA (gibberellin) biosynthesis inhibitors were added to the culture medium. Paclobutrazol and compounds belonging to the group of cyclohexanetriones clearly reduced flowering-stem growth under light conditions and vegetative-stem growth under dark conditions. Under light conditions, flower bud initiation was not affected. These and other results suggest that GA₁ may be synthesized during the in vitro culture period and that it controls flowering-stem growth but not floral initiation.Abbreviations CCC chlormequat chloride - GA gibberellin - LAB 198 999 3,5-dioxo-4-butyryl-cyclohexane carboxylic acid ethyl ester - BAS 111..W 1-phenoxy-3-(1H-1,2,4-triazol-1-yl)-4-hydroxy-5,5-dimethylhexane     

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.     

Effect of tetcyclacis and chlormequat applied to seed on seedling growth of triticale cv. Lasko

The growth of triticale seedlings from seeds treated with three concentrations of the plant growth regulators (PGRs), tetcyclacis and chlormequat, with or without drying after soaking was studied. Both tetcyclacis and chlormequat inhibited shoot growth. They reduced shoot:root ratios, first by restricting shoot growth (one week after treatment) and later by boosting root growth (eight weeks after transplanting). At the concentrations used tetcyclacis was a more active PGR than chlormequat and promoted tiller production. Drying, after soaking, promoted root growth, retarded the elongation growth of seedlings and enhanced some of the effects of the PGRs. Analyses of regressions between those growth characteristics significantly influenced by PGRs and the concentration revealed a quadratic relationship.     

Effects of exogenous gibberellins and paclobutrazol on floral stalk growth of tulip sprouts isolated from cooled and non-cooled tulip bulbs

The involvement of gibberellins (GAs) in the regulation of floral stalk elongation and flower development has been studied in tulip. The biological activity of GA₄ and GA₉, both endogenous in tulip bulb sprouts, and GA₁, was tested in vitro on sprouts of cooled and non-cooled tulip bulbs ( Tulipa gesneriana L. cv. Apeldoorn), in the presence or absence of the GA biosynthesis inhibitor paclobutrazol. At early starting dates of incubation, floral stalks from both cooled and non-cooled bulbs hardly showed any elongation in the absence of exogenous GA. Paclobutrazol had no effect on floral stalk elongation, and the response to GAs of sprouts from cooled bulbs was greater than that of sprouts from non-cooled bulbs. At later starts of incubation, considerable floral stalk elongation occurred without GA application. Paclobutrazol inhibited this floral stalk elongation, and the growth of sprouts from both cooled and non-cooled bulbs was stimulated by GA application. The effect of paclobutrazol was reversed by simultaneous application of GA₄ or GA₉. Application of GA with and without paclobutrazol resulted in the same elongation of the floral stalk, indicating the absence of substantial side effects of the inhibitor. The isolated sprouts did not develop a full-grown flower without the addition of GA. GA₄ was more effective than GA₉ in stimulating this flower development. The results demonstrate that both sprouts from cooled and non-cooled bulbs are responsive to exogenous GAs in vitro, and may be a site of GA biosynthesis.     

Inhibition of Gibberellin Production in the Fungi Gibberella fujikuroi and Sphaceloma manihoticola by Plant Growth Retardants

The effect of different types of plant growth retardants on fungal gibberellin (GA) formation has been studied in cultures of Gibberella fujikuroi and Sphaceloma manihoticola. Quaternary ammonium compounds (chlormequat chloride, mepiquat chloride, Amo-1618), triazoles (uniconazole and several experimental compounds), and the norbornanodiazetine tetcyclacis inhibited GA biosynthesis in both fungal species. Concentrations between 2 × 10⁻⁴ and 10⁻⁹m were required for a 50% inhibition of the production of gibberellin A₃ in Gibberella fujikuroi and of giberellin A₄ in Sphaceloma manihoticola. The formation of other prominent GAs was affected at a similar degree of intensity. Tetcyclacis was the most active compound in both fungi. Compared to the growth retardants mentioned above, the biological activity of chlorphonium chloride was low. The acylcyclohexanediones prohexadione and LAB 198 999 had virtually no activity. Most likely, this lack of activity is due to a rapid metabolism of the compounds in the cultures. For the triazole-type compounds and tetcyclacis, a relatively distinct correlation exists in their ability to inhibit GA formation in fungal cultures, to block ent-kaurene oxygenase in a cell-free system, and to reduce shoot growth of rice seedlings. Due to differences in their metabolic fate and species specificities, such conclusions cannot be made for the other compounds.     

Reduction of generation time in Eucalyptus globulus

The plant growth retardant paclobutrazol was applied by foliar spray to seedlings of Eucalyptus globulus (Labill.) to determine its effects on reproductive activity. It was shown to induce flowering in vegetatively juvenile seedlings and increase reproductive activity in vegetatively adult material. The former case represented a 50% (three year) reduction in generation time for commercial seedlings. Paclobutrazol treatment did not appear to have a negative effect on any aspect of reproductive development, germination of new seed, or early seedling growth, while having a distinct positive effect on reproductive output. This suggests that paclobutrazol may be an effective tool enabling tree breeders to reduce generation time and increase reproductive output in E. globulus. Foliar spraying during autumn was shown to be an effective means and timing of paclobutrazol application, with results evident in the following flowering season. Considerable persistence of paclobutrazol effects was noted in the second season after application. Pot size and growth temperatures also play roles in determining the extent of new reproductive activity each season in E. globulus seedlings.     

Interactive effects of GAs,CKs and growth retardants on the germination of celery seeds

The germination of whole seeds of celery (Apium graveolens L.) was inhibited by paclobutrazol, ancymidol and lower concentrations of uniconazole. The growth retardants daminozide, AMO 1618 and chlormequat chloride inhibited the germination of cut seeds only, indicating that the seed coat prevents the penetration of these compounds at the examined concentrations. Application of a mixture of the gibberellins A4 and A7 (GA 4/7) reversed the inhibition of all the examined growth retardants. Cytokinins (artificial or natural) had no effect when applied alone and did not interact with GA4/7 in the light. However, in the dark the cytokinins at some concentrations and GA4/7 had a synergistic effect in reversing the inhibition caused by growth retardants to whole seeds or in promoting the germination of whole seeds. It is therefore suggested that the major effect on seed of exogenous cytokinins when applied together with GA's is to increase the uptake of gibberellins by the seeds.Abbreviations AMO 1618 (2 isopropyl-5-methyl-4-trimethylammonium chloride-phenyl-1-Piperidinium-carboxylate - ancymidol -cyclopropyl-[4-methoxyphenyl]-5-pyrimidinemeth anol] - chlormequat chloride 2-chloroethyltrimethylommonium chloride - daminozide succinin acid 2,2-diamethyl hydrazide - paclobutrazol [2 RS, 3 RS]-1-(4-chlorophenyl)-4,4-dimethyl-2-(1 H-1,2,4-triazol-1-yl) pentan-3-ol - uniconazole (E)-1-(P-chlorophenyl)-4,4-dimethyl-2-(1,2,4 triazol-1-yl)-1 penten-3-ol     

Camptothecin and 10-hydroxycamptothecin accumulation in tender leaves of Camptotheca acuminata saplings after treatment with plant growth regulators

The effect of plant growth regulators (PGRs) on the accumulation of the alkaloid camptothecin (CPT) and its analogue 10-hydroxycamptothecin (HCPT) in tender leaves of Camptotheca acuminata saplings was studied. In screening experiments for PGRs, 40?mg/L dose of thiourea, triacontanol, and ascorbic acid (V_C) had no positive effects on the accumulation of the alkaloids. However, treatments with 40?mg/L of chlormequat chloride (CCC), choline chloride, paclobutrazol (PBZ), and daminozide (B₉) induced CPT and HCPT accumulation in both pre-harvest and postharvest stages. On that basis, five levels of PGRs at 0, 20, 40, 60, 80?mg/L were sprayed on tender leaves of C. acuminata saplings at pre-harvest and postharvest stages. Treatment by 40?mg/L CCC dramatically enhanced HCPT production by 308?% in pre-harvest, treatment by 60?mg/L CCC enhanced HCPT production by 100?% in postharvest. Spraying the leaves with 60?mg/L choline chloride resulted in 94?% increase of CPT and spraying with 40?mg/L of the PGRs reached 167?% increase of HCPT in the pre-harvest treatment, respectively; treatments with 60?mg/L choline chloride resulted in 64?% increase of CPT and 525?% increase of HCPT in postharvest, respectively. 52?% increase of CPT and 86?% increase of HCPT in pre-harvest, 22?% increase of CPT and 33?% increase of HCPT in postharvest were obtained by spraying leaves with 60?mg/L PBZ. Treatments with 40?mg/L B₉ had the highest impact on CPT (12?% increase in pre-harvest, 11?% increase in postharvest) and HCPT (167?% increase in pre-harvest, 173?% increase in postharvest) accumulation. The optimal PGR for obtaining the highest levels of CPT and HCPT was treatment with 60?mg/L choline chloride. In most case, the pre-harvest treatment was better than the postharvest one. These preliminary results suggest that the application of PGRs may be a useful and feasible method to increase CPT and HCPT levels in C. acuminata.     

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.     

生长调节剂处理对银杏结实的影响

盛花期对银杏雌株叶面喷施多效唑,B9,GA3,GA3＋6－BA。结果表明,多效唑和B9能够明显提高坐果率,有效增加来年成花数量,GA3和GA3＋6－BA对提高坐果无影响,但能增加种子重量,促进纵,横径增加,GA3还能够促进翌年成花数量,多效唑处理提高产量的原因,一是抑制树体营养生长,二是减少落花落果,增加植株翌年成花量。     

Opposing effects of plant growth regulators via clonal integration on apical and basal performance in alligator weed

植物生长调节剂通过克隆整合对空心莲子草顶端和基部生长的不同作用 入侵植物不仅对全球生物多样性造成了巨大的威胁,同时也严重影响了农业生产与粮食安全。克隆整合使得相连植株进行资源共享,能促进入侵植物的生长从而获得优势。然而,入侵杂草 在植物调节剂(plant growth regulators, PGRs)影响下的克隆整合作用则很少有报道。PGRs被广泛应用于 农作物生产上,并能通过土壤淋溶、侵蚀和径流作用,影响分布在作物附近的农田杂草的生长。本 研究采用两种PGRs赤霉素(gibberellins, GA)和多效唑(paclobutrazol,PAC)处理恶性入侵杂草空心莲子草 (Alternanthera philoxeroides)基端,并保持或者通过剪切达到控制基端与顶端的连通,从而探究克隆整合作用在空心莲子草响应两种农业常用PGRs中的作用。研究结果表明,GA和PAC对空心莲子草生长的作用相反。GA通过克隆整合作用显著促进顶端植株的地上生长。相反地,PAC显著抑制基端和顶端的地 上生长,但是能够通过克隆整合作用显著促进基端和顶端的地下生长。这些研究结果解释了克隆整合作用能促进PGRs对空心莲子草生长的促进作用,这很可能是外来杂草能够成功入侵人为干扰较多的农业生态系统的重要原因之一。     

Effect of paclobutrazol on water stress-induced ethylene biosynthesis and polyamine accumulation in apple seedling leaves

Ethylene biosynthesis and polyamine content were determined in [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol] (paclobutrazol) pre-treated and non-treated water-stressed apple seedling leaves. Paclobutrazol reduced water loss, and decreased endogenous putrescine spermidine content. Gibberellic acid (GA) counteracted the inhibitory effect of paclobutrazol on polyamine content. Paclobutrazol also prevented accumulation of water stress-induced 1-aminocyclopropane-1-carboxylic acid (ACC), 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), ethylene production and polyamines in apple leaves. α-Difluoromethylarginine (DFMA), but not α-difluoromethylornithine (DFMO), inhibited the rise of putrescine and spermidine in stressed leaves. S-Adenosylmethionine (SAM) was maintained at a steady state level even when ethylene and the polyamines were actively synthesized in stressed apple seedling leaves. The conversion of ACC to ethylene did not appear to be affected by paclobutrazol treatment.     

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.     

Modification of growth, yield and lodging response of lentil to phosphorus by paclobutrazol

A foliar application of paclobutrazol (1 litre a.i. ha“¹) was applied before flowering of lentils grown with different levels of phosphorus (0, 20, 40, 60, 80 and 100 kg P₂0₅ ha”¹). Increasing amounts of P up to 80 kg ha“¹ increased plant height, crop dry matter and grain yields but also increased crop lodging. Paclobutrazol decreased plant height and lodging and increased grain yield. Maximum yields were obtained with a combination of 80 kg P ha”¹ and paclobutrazol.     

Contribution of the wheat (Triticum aestivum L.) flag leaf to grain yield in response to plant growth regulators

In West-Europe, intensive cereal management uses plant growth regulators (PGRs) especially for wheat. A green-house experiment compared the effects of two PGRs on flag leaf characteristics and yield of winter wheat. Chlormequat chloride + choline chloride (CCC) and chlormequat chloride + choline chloride + imazaquin (CCC+I) were applied to winter wheat at growth stage 5 (Feekes Large scale). CCC and CCC+I significantly increased flag leaf surface area at anthesis. Both treatments also enhanced chlorophyll content of the main stem flag leaf. The grain filling period was extended with PGR application by 2 days. CCC and CCC+I significantly increased net CO₂ assimilation rates during the flag leaf life. No effects of PGR spraying were observed on the pattern of ¹⁴C labelled assimilate distribution. Increased grain yield was due to the increase in average grain weight. The results indicate that PGR treatments increased flag leaf contribution to grain filling. The addition of imazaquin (I) to chlormequat (CCC) improved the effects of CCC.     

Paclobutrazol Inhibits Abscisic Acid Biosynthesis in Cercospora rosicola

Three plant growth regulators, paclobutrazol, ancymidol, and decylimidazole, which are putative inhibitors of gibberellin (GA) biosynthesis, were studied to determine their effect on abscisic acid (ABA) biosynthesis in the fungus Cercospora rosicola. All three compounds inhibited ABA biosynthesis, and paclobutrazol was the most effective, inhibiting ABA 33% at 0.1 micromolar concentrations. In studies using (E,E,)-[1-¹⁴C] farnesyl pyrophosphate, it was shown that ancymidol blocked biosynthesis prior to farnesyl pyrophosphate (FPP), whereas paclobutrazol and decylimidazole acted after FPP. The three inhibitors did not prevent 4′-oxidation of (2Z,4E)-α-ionylideneacetic acid. C. rosiciola metabolized ancymidol by demethylation to α-cyclopropyl-α-(p-hydroxyphenyl)-5-pyrimidine methyl alcohol. Paclobutrazol was not metabolized by the fungus. Information that these plant growth regulators inhibit ABA as well as GA biosynthesis should prove useful in determining the full range of action of these compounds.