Roger Menhenett

Comparison of a new triazole retardant paclobutrazol (PP 333) with ancymidol, chlorphonium chloride, daminozide and piproctanyl bromide, on stem extension and inflorescence development in Chrysanthemum morifolium Ramat

Abstract Several experiments in glasshouses at different times of the year have demonstrated that a new growth retardant, paclobutrazol (PP 333), applied as a single compost drench or as a foliar spray, is very effective in controlling stem extension in the pot chrysanthemum ( Chrysanthemum morifolium ) ‘Bright Golden Anne’, a tall cultivar. Moreover, the concentration required, 30–50 mg a.i. l −1 , was much lower than with a drench of chlorphonium chloride (Phosfon/Phosfleur), or with a foliar spray of daminozide (Alar/B-Nine) or piproctanyl bromide (Alden/Stemtrol). In two trials, a comparison of paclobutrazol and ancymidol (A-Rest/Reducymol) drenches indicated that, on a weight basis, the two compounds induced approximately equal dwarfing, whereas foliar sprays of paclobutrazol were more active than those of ancymidol, particularly at the lower concentrations. As before, at least 50–100 times the concentration of daminozide was needed than of paclobutrazol or ancymidol in order to induce an equivalent response. However, the variability in lateral stem length within a pot of 12 flowering shoots was a little higher with foliar sprays of paclobutrazol than with daminozide, possibly indicating that the amount of paclobutrazol transported to its site(s) of action varied more between shoots. Paclobutrazol produced similar delays in flowering (which invariably accompany commercially adequate reductions in plant height) to ancymidol and daminozide, whereas the delays with chlorphonium chloride and piproctanyl bromide were 2–4 days greater. In an experiment with the dark pink ‘Regal Anne’, daminozide caused some loss of flower pigmentation, but paclobutrazol and the other compounds did not.

Response of potted tulips to new and established growth-retarding chemicals

Abstract A range of growth-retarding chemicals was evaluated for their potential in the production of compact pot-grown tulips: ancymidol, piproctanyl bromide (Alden), dikegulac-sodium (Atrinal), a phenyl tetrazole compound (coded PP528), 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (coded UBI-P293), chlorphonium chloride (Phosfon), 2-chloroethylphosphonic acid (Ethrel), and 5 morphactins. All chemicals were applied as single soil drenches 1–2 days after transferring plants to the glasshouse. Mid- and late-season forced bulbs of cultivars ‘Apeldoorn’, ‘Paul Richter’ and ‘Rose Copland’ were used. Piproctanyl bromide and chlorphonium chloride were ineffective, the former causing some stimulation of top internode extension. Ethrel at high concentrations gave a slight reduction in first internode length only, associated with a degree of flower-bud blasting. Dikegulac-sodium gave some reduction in stem and petal length, depending on cultivar. PP528 induced flower-bud blasting, adverse changes in flower colour and reduced petal length at concentrations which effectively shortened stems. Morphactins were toxic or caused flower-bud blasting and other floral abnormalities at high concentrations; at lower doses most morphactins reduced first internode length, while some increased length of the upper internodes, inducing nastic curvature and occasionally altering flower shape. Most effective height control was achieved with ancymidol and UBI-P293, the latter being the more active (at the concentrations tested); flower quality was good. In one experiment only, ancymidol slightly delayed flowering. High concentrations of UBI-P293 gave rise to some flower-bud blasting, especially in ‘Rose Copland’ which showed other adverse side-effects such as decreased length and longevity of the flowers, not only with UBI-P293 but also with higher doses of some other retardants.

Chemical “pinching” of pot chrysanthemums with 2,3-dihydro-5,6-diphenyl-1,4-oxathiin

Abstract In summer and winter experiments a research formulation of 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (code name UBI-P293) was effective as a chemical “pinching”-agent on pot chrysanthemum cultivar ‘Bright Golden Anne’, when applied at 0.4 and 0.8% active ingredient to the apical region of plants within a few days of planting. A lower concentration was not so effective. When the applications were made later, they induced considerable variation in the length and quality of lateral shoots and also delayed flowering. The compound did not always prevent the development of the terminal bud, but reduced apical dominance sufficiently to permit the lateral shoots to develop normally. When P293 successfully “pinched” the plants in the winter experiment, it had no effect on the length of the lateral shoots which developed. At flowering these were too long from a commercial growers point of view. In the summer experiment shoot length was adequately reduced by application of a foliar spray of a new quaternary ammonium growth retardant when the lateral shoots were a few centimetres long.

An evaluation of new growth retardants on Mid-Century Hybrid lilies

Abstract The new growth retardants piproctanyl bromide (Alden or Stemtrol), dikegulac-sodium (Atrinal), PP 528 (a phenyl tetrazole compound) and 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (coded UBI-P293) were compared with the established compounds chlormequat chloride (Cycocel), ancymidol (A-Rest or Reducymol) and chlorphonium chloride (Phosfon), for their ability to dwarf Mid-Century Hybrid lily cultivars ‘Enchantment’ and ‘Joan Evans’. Single compost drenches were given 2–3 weeks after transferring plants to the glasshouse. Piproctanyl bromide at high concentrations (2000 mg a.i. per plant) produced some dwarfing, as did chlorphonium chloride (at 250 mg a.i. per plant). Chlormequat chloride produced a similar response at 1250 mg a.i. per plant, but on a concentration basis ancymidol was by far the most active compound (only 0.25–0.50 mg a.i. per plant was required). Plant and flower quality was generally good with these 3 chemicals. Dikegulac-sodium reduced stem length but prevented the development of flower buds and the plants senesced. PP 528 also restricted stem extension but plant quality was unsatisfactory; increasing concentrations led to smaller florets, weaker stems and drooping leaves. UBI-P293 produced as great a reduction in stem length as did ancymidol, and 100 mg a.i. per plant was as active as 500 mg. However, as the concentration was raised there was a decrease in floret size and number.

The responses of virus-free and virus-infected lily ‘Enchantment’ to the retardants ancymidol, chlormequat chloride, mepiquat chloride and BTS 44 584, a ternary sulphonium carbamate

Abstract The new growth retardants mepiquat chloride (a quaternary ammonium compound of the piperidinium type, coded BAS 083 00W) and a ternary sulphonium carbamate (coded BTS 44 584) were compared with ancymidol (A-Rest or Reducymol) and chlormequat chloride (Cycocel) for their ability to dwarf virus-free and virus-infected (ordinary) Mid-Century Hybrid lily cultivar ‘Enchantment’. Single compost drenches were given 3 weeks after transferring plants to the glasshouse. Compared with the virus-infected control plants, virus-free controls were 62% taller and 33% greater in leaf spread; floret number was approximately doubled and floret diameter was increased by 12%, but flowering was delayed by 6.5 days. The length of the lower stem bearing dead leaves was 15% of the total in virus-infected controls and 3% of the total in virus-free controls. Ancymidol, chlormequat chloride and mepiquat chloride were all effective growth retardants, and were without adverse side-effects. On a concentration basis, mepiquat chloride was 2–2.5 times as active as chlormequat chloride in reducing stem extension, but ancymidol was several orders of magnitude more active than both those compounds. With BTS 44 584, the maximum reduction in stem length obtained was 16% compared to controls. The decreases in stem extension were more pronounced, in both percentage and absolute terms, in the virus-free bulbs. Nevertheless, for a given retardant treatment, plants of the virus-free stock remained taller than those of the virus-infected stock. As a result, 2–3 times the amount of an active retardant was required by virus-free than by virus-infected plants in order to produce similar stem lengths at flowering. Effects of the retardants on the time of flowering, flower number, floret diameter and leaf spread were small, but increasing concentrations of all chemicals progressively increased the proportion of the stem bearing dead leaves. The effects of ancymidol, chlormequat chloride and mepiquat chloride persisted in the year after treatment.

Responses of potted tulips to novel growth-retarding chemicals and interactions with time of forcing

Abstract The effects of the growth retardants ancymidol and 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (coded UBI-P293) were compared on early-, mid- and late-season forced tulip bulbs of cultivars ‘Apeldoorn’, ‘Paul Richter’ and ‘Rose Copland’. The chemicals were applied as single soil drenches, 1 day after transferring plants to the glasshouse. These treatments did not affect flower or petal length nor delay flowering, but high concentrations resulted in increased floral bud blasting in early-season ‘Apeldoorn’ (with ancymidol only) and in early- and mid-season ‘Rose Copland’ (with UBI-P293 only). Both ancymidol and UBI-P293 effectively dwarfed plants of all 3 cultivars at each time of forcing, provided sufficiently high concentrations were selected. However, early- and mid-season ‘Apeldoorn’ plants were particularly responsive to these compounds, the highest doses of which resulted in reductions in stem length at flowering of 70–80% (for ancymidol) or 50–60% (for UBI-P293); similar doses achieved less dwarfing in ‘Paul Richter’ and ‘Rose Copland’ and in late-season ‘Apeldoorn’. In ‘Apeldoorn’ and ‘Paul Richter’, ancymidol reduced extension markedly in the first internode, with less effect distally; UBI-P293 was effective in reducing extension of all internodes. Compost drenches of 3 newer growth retardants were also evaluated. Mepiquat chloride had no effect on flowering except that floral bud blasting was increased in ‘Rose Copland’. The stem responses of ‘Paul Richter’ and ‘Rose Copland’ to mepiquat chloride were trivial, but in ‘Apeldoorn’ the highest dose tested (2500 mg a.i./pot) reduced overall stem length via an effect on first internode extension. A quaternary sulphonium carbamate (coded BTS 44 584) had no effects on flowering or stem extension at concentrations up to 2500 mg a.i./pot. An N -carbamoylimidazole (coded BTS 34 723), tested at 1–50 mg a.i./pot, had small effects on internode extension which depended on cultivar, but potentially useful dwarfing was not observed.

Comparisons of a new triazole retardant PP 333 with ancymidol and other compounds on pot-grown tulips

PP 333 was compared with ancymidol, CGA 65993, dikegulac-sodium (as Atrinal) and maleic hydrazide for its ability to restrict stem extension in tulip cvs ‘Paul Richter’, ‘Apeldoorn’ and ‘Trance’. Single, 300 ml compost drenches were applied one day after housing fully cooled bulbs grown in a sphagnum peat/sand compost (3:1 v/v).Experiments in 1979/1980 and 1980/1981 with mid- and late-season crops showed that PP 333, like ancymidol, could reduce stem extension without deleterious responses. However, higher amounts of PP 333 (0.8–33.3 mg a.i./pot) were required than of ancymidol (0.625–2.5 mg a.i./pot). Cv. Paul Richter was much less responsive to PP 333 and ancymidol than ‘Apeldoorn’, particularly when grown as a late-season crop. Dikegulac was the most effective chemical in the latter situation, especially as it restricted post-flowering extension growth. PP 333 and ancymidol were better able to control such growth in the mid-season crops. Other than for the above purpose, dikegulac proved unsuitable because it increased flower bud blasting and gave rise to abnormally coloured perianth segments. Similarly, marked reductions in stem length of ‘Apeldoorn’ and ‘Paul Richter’ with CGA 65993 were associated with unacceptable side-effects, namely, smaller flowers (both cvs) and more bud blasting in ‘Apeldoorn’. Maleic hydrazide (5–500 mg a.i./pot) had little influence on stem length in any of the three cultivars.The trials indicated the need to test each cultivar/retardant combination, as well as to take into account the time of forcing because, whereas ‘Paul Richter’ and ‘Apeldoorn’ were adequately dwarfed by PP 333 and ancymidol without adverse effects, both compounds caused about 50% of ‘Trance’ flowers to blast. No treatment influenced flowering date in cv. ‘Paul Richter’ but PP 333 delayed flowering by two days in ‘Apeldoorn’ and ‘Trance’, as did the higher doses of ancymidol in ‘Apeldoorn’.

Gibberellins and Cytokinins from Excised Shoots of Chrysanthemum morifolium Ramat. Using Agar Diffusion and Tissue Extraction Methods

Summary Young axillary shoots of Chrysanthemum morifolium RAM AT. cv. Bright Golden Anne with developing inflorescences were excised and inserted into a solid agar medium (1.5%, containing 2% sucrose and 0.01 M phosphate buffer) in a Fisons Growth Cabinet (20°C and short photoperiods), to allow gibberellins (GAs) and cytokinins to «diffuse» into the agar. Acidic ethyl acetate-soluble (AES) and water-soluble (WS) GAs were detected in purified extracts of shoots and agar by means of the lettuce hypocoryl bioassay and, when amounts were calculated in terms of gibberellic acid equivalents, there was evidence that GAs were «produced» during the diffusion periods. Thus, the total GA content of the shoots harvested at the end of the three successive 24 hour periods of diffusion plus that in the agar itself was 8.4 (Experiment 1) and 3.7 (Experiment 2) times as great as that found in samples of shoots taken initially. The term «produced» is preferred to «synthesized» because of the possibility that interconversion of AES and WS GAs might have occurred in the shoots (or possibly in the agar, andlor during the early stages of the extraction and purification procedures). There was no indication that butanol-soluble cytokinins, as quantified by the soyabean callus bioassay in terms of zeatin equivalents, were synthesized or produced in Chrysanthemum shoots since, although small quantities of cytokinins were detected in the agar, a greater amount of these phytohormones was lost from the shoots during diffusion.

Interactions of daminozide, 2, 2′-dipyridyl, and gibberellins A3, A9 and A20, in stem extension inChrysanthemum morifolium Ramat: an indication that daminozide may not inhibit the responses to GA9 or GA20 by blocking gibberellin hydroxylation

Interactions between the growth retardant daminozide (a substituted succinamic acid) and a subsequent application (1 or 10 μg) of either gibberellin A3, A9 or A20, on stem extension inChrysanthemum morifolium cv. Bright Golden Anne, indicated that pre-treatment of plants with daminozide largely prevented the response to GA20 as well as to GA9. The daminozide-GA3 interaction on total stem length was dependent upon the dose of GA3 such that, by flowering time, 1 μg of GA3 had virtually eliminated the retardant effect, while 10 μg of GA3 increased stem length to a value similar to that achieved by control shoots receiving 10 μg of GA3. In contrast, prior application of 2, 2′-dipyridyl (an inhibitor of hydroxylation in some plant and animal systems) had no significant influence on the time courses of response to any of the GAs. In the absence of daminozide (and 2, 2′-dipyridyl) all three GAs were very active in promoting internode extension soon after their application. If 2, 2′-dipyridyl can block hydroxylation reactions in chrysanthemum tissues, the results do not support the hypothesis that daminozide restricts GA9- (or GA20-) induced stem elongation by preventing the hydroxylation of GA9.