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).
Salpiglossis sinuata R. et P., a floriferous member of the Solanaceae, was studied for potential as a flowering potted plant when modified by growth retardants. Seedlings of an inbred line P-5 were covered with black cloth for an 8-hour photoperiod to permit vegetative growth to ≈16 -cm-diameter rosettes. Plants were then exposed to an 18-hour photoperiod for the duration of study. Flowering occurred 40 days after the plants were transferred to long days. Neither spray applications of uniconazole at 10, 20, 40, or 100 ppm, nor chlormequat chloride at 750, 1500, or 3000 ppm significantly retarded plant height. Applications of daminozide, ranging in concentration from 1000 to 5000 ppm, alone and in combination with chlormequat chloride, were effective at retarding plant height; however, concomitant restriction of corolla diameter was frequently observed. Chemical names used: 2-chloro- N,N,N -trimethylethanaminium chloride (chlormequat chloride); butanedioic acid mono(2,2-dimethylhydrazide) (daminozide); and (E) -1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl) -1-penten-3-01 (uniconazole).
Various rates of ancymidol granular incorporated, granular broadcast, soil drench, and foliar spray treatments were tested on 7 breeding plant species. Generally, treatment of media affected plant height more than foliar sprays. Media treatments reduced height linearly, with increasing rates reducing plant height. Effects were similar for Salvia splendens F. Sellow ex Roem. & Schultz and Pelargonium × hortorum L.H. Bailey plants. Height of Targetes erecta L. plants was controlled most effectively by 311 to 622 mg a.i. m−3 drenches or granular incorporated. Begonia semperflorens - cultorum Hort., and Antirrhinum majus L. plant height was best controlled with granular incorporated ancymidol at rates of 155 to 622 mg a.i. and 311 to 1243 mg a.i. m−3, respectively. Germination of Tagetes and Pelargonium seed was unaffected by granular incorporated ancymidol at 78 to 311 mg a.i. m−3. Chemical names used: a-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol).
Plant Cell 4 119 128 doi: 10.1105/tpc.4.2.119 10.2307/3869565 Teng, F. Zhai, L. Liu, R. Bai, W. Qiu, L. Huo, D. Tao, Y. Zheng, Y. Zhang, Z. 2013 ZmGA3ox2, a candidate gene for a major QTL, qPH3.1, for plant height in maize
Field studies were conducted during 1992 and 1993 to determine the effect of six monthly planting dates from April to September on gas exchange, plant height, and leafy fresh and dry yields of vegetable amaranth (Amaranthus tricolor L.). Vegetative growth was satisfactory for May to August planting. Seeds planted in April failed to germinate due to low soil temperatures. Plant growth was significantly reduced in the September planting possibly due to low fall temperatures and shortened day length. Soil and air temperatures 25 °C or higher promoted optimal stand establishment and growth. The vegetative growth of June seeded amaranth took place during the warmest part of the summer and as a result had maximum CO2 exchange rate (CER), plant height, and leafy fresh and dry yields. The relationship between planting date and CER, transpiration rate (E), stomatal conductance (gs), plant height, and leafy fresh and dry yields was quadratic, while a cubic equation provided best fit between the planting date and internal leaf CO2 concentration (Ci). The results suggest that it is possible to stagger the planting of Amaranthus tricolor in the southeastern United States to assure availability of fresh leafy greens throughout the summer. However, the crop produces maximum leaf biomass when grown during the warmest part of the summer.
Flowering time, plant height and weight of Zinnia elegans Jacq were reduced by 4 weeks of 9 hour photoperiods. Multiple application of butanedioic acid mono-2, 2 dimethyl-hydrazide (daminozide) reduced plant height and flower diameter but increased time to flower without affecting fresh weight while ancymidol restricted height and fresh weight but not time to flower.
Daily water use for potted Chrysanthemum ×morifolium Ramat. ‘Spirit’ was estimated from pan evaporation and plant height data collected over 2 seasons using 3 different growing environments (glass greenhouse, saranhouse, and outside—no structure). Regression equations derived using pan evaporation and plant height were not significantly improved with the inclusion of plant width as an additional variable to estimate water use.
Height reduction of sweet corn (Zea mays L.) plants by head smut [Sphacelotheca reiliana (Kuhn) Clinton] was measured in four field studies using seed furrow inoculation. Infected plants were consistently stunted whether sori occurred on the ears only or on ears and tassels. There was a significant relationship between plant height and infection of individual plants. Difference in mean height between plants later determined to be infected or non-infected was measurable 5 weeks after planting and increased steadily until growth ceased. This suggested the possibility of elimination of weaker plants in segregating populations before maturity. Mean height reduction of individual hybrids and inbred lines ranged from 7% to 65% of the height of non-infected plants, with an average of ≍30% reduction for all cultivars. Correlations between mean percent height reduction and disease incidence of cultivars were variable and generally low, ranging from r = −0.34 to 0.17. This suggested that degree of height reduction would be a poor indicator of the susceptibility of a cultivar to infection.
The influence of removal of specific wavelengths [red (R), blue (B), and farred (FR)] from sunlight on the height of chrysanthemum plants was investigated by overlaying Roscolux™ colored acetate films on 4% CuSO4 or water (control) spectral filters. CuSO4 filters removed FR wavelengths and significantly reduced plant height and internode length compared to control plants that received B, R, and FR wavelengths of light. Plants grown under Roscolux blue filters did not receive R light and were significantly taller compared to plants from any other treatments. Plants grown under Roscolux red filters did not receive B light and were significantly shorter compared to plants from other treatments. Leaf area, leaf dry weight, and stem dry weight were highest in plants grown under Roscolux red and control filter combination. The amount of leaf chlorophyll and the ratio of Chl A: Chl B was highest in plants grown under Roscolux blue filters. In general, plants that received FR light (control + film) were taller than the plants that did not receive FR light in the corresponding (CuSO4 + film) filter combination. The influence of removal of specific wavelengths on plant height control and developmental physiology will be discussed.
Potted plants of Lilium longiflorum Thunb. cvs. `Ace' and `Nellie White' were grown either under an ambient photoperiod (APP) or under an 8-hour photoperiod (8PP) in a greenhouse. The latter photoperiod was achieved by pulling black cloth over the plants at 1615HR and removing the cloth at 0615HR each day, from emergence to flowering. Within each photoperiod, ambient light intensity was reduced by 0, 20, 40 or 60% using various shade cloths permanently suspended above the plants. Heating was set at 20/16C for the dark/light period, respectively. Plant height, determined from the rim of pot to the top of plant, was 25% lower under 8PP compared to APP for both cultivars. Plant height of `Ace' and `Nellie White' increased by 1.5 mm and 2.5 mm, respectively, per 1% light reduction.