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  • Author or Editor: Roy M. Sachs x
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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.

Open Access
Authors: and

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.

Open Access

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).

Open Access

Flowering of brodiaea (Triteleia laxa syn. Brodiaea laxa `Queen Fabiola') did not have an obligate requirement for manipulation of temperature or photoperiod. Vernalization of corms reduced the greenhouse forcing phase but did not alter the number of flowers per inflorescence or scape length. Long photoperiods hastened flowering but decreased flower quality and flowering percentage. Scape length, which was not affected by photoperiod or mother corm size, was increased when plants were grown at night temperatures < 10C. Diameter of the apical meristem in the dormant corm, flowering percentage, and flower quality were not affected by a 10-fold increase in corm size above a critical weight (0.6 g). In contrast, the weight and number of daughter corms were closely correlated with mother corm size. The optimum planting depth for brodiaea corms was 10 cm below the soil surface.

Free access

Exposure of dormant corms of Triteleia laxa `Queen Fabiola' to 20 ppm C2H4 for 7 days promoted flowering of small corms and resulted in increased apical meristem size, early sprouting, early flowering, more flowers per Inflorescence, and increased fresh weight of daughter corms and cormels. The respiration rate of the C&treated corms increased to four to five times that of the controls during the 7-day treatment, declined markedly after termination of the C2H4 treatment, but remained higher than that of the controls. The C2H4 effects were associated with increased growth rate and consequently a greater final size of the apical meristem (determined by scanning electron microscopy). Leaves produced by C2H4-treated corms were wider, longer, and weighed more than those of the controls.

Free access