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Abstract
Although at each shoot apical meristem, vegetative and reproductive development represent alternative courses of differentiation, we wish to emphasize the quantitative interaction between these two processes particularly with regard to the potential for chemical control. Without exception the known flower promoting or inhibiting substances also have substantial influence on vegetative development (32).
Abstract
Although for an entire plant, vegetative and reproductive development may proceed concurrently, at each shoot apical meristem a transition occurs from leaf production to bract or sepal production at the time of flower initiation. Subsequent stages of reproductive development are equally differentiated from that of vegetative development. Hence, vegetative and reproductive development represent alternative courses of differentiation of apical meristematic tissues.
Abstract
Retardation of runner formation in the fall was obtained in summer-planted strawberry (cv. Tioga) as a result of (2-chloroethyl)trimethylammonium chloride (chiormequat) and succinic acid-2,2-dimethylhydrazide (SADH) spray treatments. No residual effects of the growth retardants on runner development were found in the following spring. The treatments brought about a significant increase in the no. of crowns per plant, but this had no effect on the total yield of the plants. Fruit quality was lowered by the treatments, especially by SADH.
Abstract
Ten compounds applied as foliar spray were screened for reducing and delaying bolting in fall-planted carrots (Daucus carota L.). Only butanedioic acid mono-(2,2-dimethylhydrazide) (daminozide) was effective; seedstalk height was reduced and root size was unaffected. Daminozide effectiveness was greatest in weak-bolting cultivars. Two sprays of 5000 ppm, 2 weeks apart at about 4 and 2 weeks prior to natural bolting were most effective, suggesting that daminozide does not interfere in the cold temperature induction process, but rather has a delaying and inhibitory effect on the initial seedstalk elongation. Two sprays of 500 liters/ha of daminozide solution of 5000 ppm gave promising results. Root quality was improved without influencing carrot yield or dry matter content. Although (2-chloroethyl)trimethymammonium chloride (chlormequat) suppressed bolting in some experiments, it was less effective than daminozide at comparable rates and higher rates decreased yield.
Abstract
In Coprosma baueri Endl. low response to foliar sprays of 1% daminozide (SADH; succinic acid 2,2 dimethyl hydrazide) was accounted for, in part, by low levels of endogenous SADH in the terminal shoot tissues. The same exogenous application rates to Xylosma congestum (Lour.) Merr. and Pyracantha coccinea Roem. caused greater inhibition of stem elongation and higher endogenous levels of SADH. However, the most significant results of this study were that a negligible relationship existed between level of SADH in tissues of elongating branches and the inhibition of stem elongation. Elongation did not increase in stems of Xylosma, Coprosma and Pyracantha after 60 to 90 days even though endogenous SADH concentration decreased sharply in this interval. We concluded, therefore, that only a portion of the SADH found in tissues was active in inhibiting stem elongation. Multiple applications of SADH, made after pruning but before branch elongation had begun, caused greater inhibition of elongation than was expected on the basis of endogenous levels of SADH. This response suggested that exogenous applications reached sites in axillary buds critical for inhibition of elongation more readily than endogenous SADH translocated from older leaves. The implications of these findings for interpreting comparative activity studies among analogs of growth retardants and among species is discussed.
Abstract
The postulation proposed by Reed and his colleagues (11, 12) that the mode of action of Alar was through hydrolysis of the growth retardant to unsymmetrical dimethylhydrazine, UDMH, which subsequently inhibits diamine oxidase from converting tryptamine to indoleacetaldehyde, was examined. In vitro tests showed that commercial proteolytic enzyme preparations as well as those prepared from Alar-sensitive plants were not capable of breaking the C-N (peptide) bond in Alar. Both UDMH and β-hydroxyethylhydrazine (BOH) reacted, with indoleacetaldehyde to yield several compounds which gave positive spot tests for indole and hydrazine. Likewise, UDMH reacted readily with constituents in the endosperm-nucellar tissues when injected into immature almond ovules. Experiments with Alar, UDMH and BOH showed that Alar was more effective as a growth retardant and as a promotor of floral initiation than the others at nearly equal molar concentrations. Injections of Alar and 2-14C mevalonic acid, together and separately, into immature peach ovules revealed that the synthesis of kauren-19-ol, a gibberellic acid precursor, was depressed in the presence of Alar. None of these results support the hypotheses that 1) the active portion of Alar is the UDMH moiety and 2) the primary effect of Alar is to inhibit IAA synthesis.
Abstract
In ‘Bright Golden Anne’ chrysanthemums girdling below the treated leaves does not reduce, rather it may enhance, growth retarding activity of foliar applied ancymidol. Experimental evidence with 14C sucrose shows that the compound does not pass the girdle to enter the root system, and it is assumed that ancymidol transport is similarly restricted. Our results indicate that the major site of action of ancymidol is in the shoot tissues. One suggestion accounting for greater activity of soil, as compared to foliar, applications is that the chrysanthemum root system may absorb ancymidol more rapidly than the leaves.
Abstract
Foliar application of 0.1 to 1% dikegulac-sodium [sodium 2,3:4,6-di-0-isopropyl-idene-2-keto-L-gulonate (Atrinal)] inhibited (shoot) elongation and axillary bud break for more than 3 months in field grown Xylosma congestum, (Lour.) Merr., Pyracantha coccinea (Roem.), Callistemon citrinus (Curt.), Cotoneaster pannosa (Franch.), and Nerium oleander L. Phytotoxic symptoms were minor in most species, but Nerium, chlorosis of young leaves and necrotic areas on tips of half expanded leaves were noted. Applications made immediately after pruning eliminated this problem. Fully expanded leaves were undamaged and their viability more than 5 months after treatment with 1% solutions were equal to that of control plants. Greenhouse trials with Eucalyptus globulus Labill., Fraxinus uhdei (Wenz.) lingelsh, and Ulmus parvifolia Jacq. indicated that this compound will also be a useful inhibitor for landscape tree species, although at 0.4%, phytotoxicity in Eucalyptus may be too severe for general application.
Abstract
Foliar applications of 2, 3, 4, 6-di-o-isopropyl-idene-2-keto-L-gulonate (dikegulac) at rates of 0.2-0.3% resulted in growth reductions comparable with l,2-dihydro-3,6-pyridazinedione (MH) or methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (chlorflurenol). Where terminal leaf abscission occurs, tree appearance after treatment is sometimes better than that of trees treated with either MH or chlorflurenol. Growth reduction from trunk banding with dikegulac n-pentyl ester was observed only on Ulmus parvifolia Jacq.; chlorflurenol in trunk banding has a much wider species range and is effective at lower concn.
Abstract
Chemical control of plant height has been achieved for many herbaceous and woody species. Horticultural practices in the greenhouse, orchard, and landscape have been altered to include the use of numerous compounds, the main function of which is to eliminate overgrowth. The problems encountered in selecting and using even the registered materials cannot be readily generalized since each compound presents special difficulties. Nevertheless, for the purpose of this review, 7 challenges to effective use usually presented by all compounds will be discussed, namely: 1) identifying the primary cause of inhibition of stem elongation; 2) timing the application of compounds to the appropriate stage of plant development; 3) determining the best method of application; 4) determining the optimum dosage, formulation, and frequency of application; 5) testing for cumulative phytotoxicity; 6) noting species specificity; and 7) taking note of potential environmental effects. Many chemicals have been made available for testing, but relatively few of them are registered expressly for control of overgrowth (Fig. 1).