2,3-dihydro-5,6-diphenyl-1,4-oxathiin, (UBI-P293) acts as localized blocker of cell division and expansion while well formed tissues are exempt and develop normally. When applied to vegetative chrysanthemum plants, UBI-P293 blocked development of the top 8–10 nodes; whereas lateral shoots developed at the same rate, number, and weight as those observed on manually pruned plants. When applied to plants initiating flowers, UBI-P293 caused chemical disbudding by blocking development of laterals while the terminal bud was exempt and expanded into a normal inflorescence. The optimum concentration for the 35 cultivars evaluated varied from 0.25 to 1.0% when applied between 15 to 24 short days. Higher concentrations or earlier applications of UBI-P293 inhibited all development.
Chemical growth retardants are unique in the history of chemical regulation of plants. All types thus far used by growers have been synthetics. Unlike many other classes of growth regulators, we have thus far not detected the naturally occurring chemicals that account for the development of dwarf plants. For one reason, dwarf plants may result from reduced or degenerated biosynthetic pathways for the natural production of gibberellin-like compounds. Also, they may result from the synthesis of a number of interrelated compounds, which separately have little effect on growth. In certain combinations and concentrations, however, they affect cell division and expansion control systems. Chemical growth retardants permit a direct approach to growth control by retarding internode elongation without seriously disrupting the growth processes that involve chlorophyll and phytochrome. They permit growers to predetermine the size of the plant for many different uses and have become an integral part of many plant production systems (Fig. 1). Florists’ and nurserymen’s catalogs designate cultivars as particularly responsive to a specific chemical growth retardant.
The origin of floriculture as a commercial enterprise arose from the practices developed by private estates and public parks. The motivation for excellence in crop production was for spectacular display effect at any cost. Fancy greenhouse structures were designed for growing plants which required labor-intensive techniques to bring flowering plants to the desired time of display. Secrets of growing were hoarded by growers. This was unlike the origin and the attitudes of other areas of agriculture. Field and fruit crop production evolved from a subsistence enterprise through barter or exchange to specialization and technological change. The nature of the origin of commercial floriculture was further handicapped in that its perishable products implied a limited need for duration.
Sixty-five cvs. of petunia, Petunia hybrida Vilm., were evaluated for sensitivity to ozone and the reduction in damage afforded by applications of growth regulating and other chemicals. Plants were exposed to ozone concn at 15, 30, 45, and 60 parts per hundred million (pphm) in a growth chamber for 1.5, 3, and 6 hr at 25°C, 78-88% relative humidity, and an illumination of 2,000 ft-c. Chemicals which retarded internode elongation and promoted dark green color of the foliage reduced visible injury induced by ozone.4,5 The compounds 2,4-dichlorobenzyltributyl phosphonium chloride (CBBP) and succinic acid 2,2-dimethyl hydrazide (SADH) retarded growth and modified sensitivity of the foliage to ozone. Concentration of SADH needed to reduce injury significantly was at least twice that used to retard stem elongation. Adding L. ascorbic acid and a wax coating to the spray solution increased the protection afforded by SADH. Chemicals which did not retard growth of petunia such as the chemical growth retardants (2-chloroethyl) trimethyl ammonium chloride (chlormequat), α-cyclopropyl-α (4-methoxyphenyl)-5-pyrimidine methanol (ancymidol), and the systemic fungicide methyl 1-butylcarbamoyl-2-benzimidazolecarbamate (benomyl) afforded no protection for ozone treated plants. The 65 cvs. were placed in 6 classes based on an average rating of injury after exposures to 4 doses of ozone. Five cvs. were in the very tolerant class and have most potential for use in the development of new petunia cvs. resistant to ozone and possibly to other phytotoxicants.
Eight cultivars of poinsettia, Euphorbia pulcherrima Willd., were evaluated for sensitivity to α-cyclopropyl-α (4-methoxyphenyl)-5-pyrimidine methanol (ancymidol) and protection from ozone and sulfur dioxide injury afforded by applications of ancymidol and (2-chloroethyl) trimethyl ammonium chloride (chlormequat). Foliar sprays of ancymidol were at least 80 to 500 times and the soil drench 1000 times more active than chlormequat in retarding stem elongation. The diam of the bracts was reduced, but branching increased more on plants treated with ancymidol than on untreated plants. The cv. Annette Hegg (AH) was more sensitive to ozone fumigations than was ‘Eckespoint C-l’ (C-l). Sulfur dioxide also caused more injury to AH than to C-l. Ancymidol and chlormequat reduced visible injury induced by ozone and sulfur dioxide.
The relative efficiencies of high-pressure (HPS) and low-pressure sodium (LPS) lamps for plant growth were determined for 32 species of foliage and flowering plants in greenhouse under winter conditions at 37°N latitude. HPS with a relatively wide spectral emission peaking at 589 nm, and low-pressure sodium (LPS) with a monochromatic line at 589 nm were compared at 42 W/m2 irradiance in the 400–700 nm region for various lengths of time at various times of day. Although radiation in the far-red region (700–800 nm) differed, HPS and LPS equally accelerated rates of increase in fresh weights, and heights, and flowering of most herbaceous and tropical foliage plants evaluated. High-pressure sodium and LPS were ineffective, however, in promoting growth of deciduous trees and some woody plants and had no more effect than exposure of the plants to natural winter days with 0.9 W/m2 from incandescent lamps for 8 hrs (2000-0400) night interruption (long day controls). After 16 hours, about half the species showed photomorphogical differences between plants grown at intensities of 21 and plants grown at 42 W/m2 from LPS. All showed significantly better growth characteristics (fresh weight, height, early flowering) than the long day controls. Lighting during the day or night (42 W/m2 from 0800–1600 or from 2000–0400) was equally effective in promoting growth responses with 15 of the 32 species evaluated. Night lighting was more effective than day lighting with 10 of the 32 species tested. The majority of the species grew equally well when lighted 16 hours daily (0800-2400) with 21 W/m2 or 8 hours daily (2000–0400) with 42 W/m2. Effectiveness of the lighting was generally unrelated to the photoperiodic requirements of the plants. Many of the plants, which were previously classified as day-neutral (DN), flowered as if they were long day plants. Such day-neutral plants apparently required adequate light (intensity and duration) for photosynthesis. Increased daylength alone, without regard to intensity, was not sufficient to accelerate growth and early flowering of day-neutral plants. Since HPS and LPS were equally effective on most species tested, we concluded that light quality was less important than total irradiation (energy) for the growth and early flowering of many herbaceous plants.
When compared at a level of 1 ft-c for 16 hours at a night temperature of 20°C, light from 5 types of sources delayed flowering of short-day plants (Chrysanthemum, marigold, Rieger begonia), promoted vegetative growth of 2 species of Ulmus, 2 each of Acer, and 1 of Koelreuteria, Rhododendron, Rhus, and Zelkova, and promoted flowering of long-day plants (carnation, marguerite daisy, Petunia) in the order from most to least effective: incandescent (INC) > high-pressure sodium (HPS) > > metal halide (MH) = cool white fluorescent (F) > > clear mercury (Hg). Poinsettia, Betula, Catalpa, Platanus, and Tilia continued to grow vegetatively in response to all sources. Ilex and 2 species of Pinus did not respond. Foot candles of light from HPS lamps had to be increased at least 4- to 8-fold to regulate vegetative growth of long-day plants and delay flowering of short-day plants in comparison to INC lamps. High-pressure sodium lamps were ineffective in promoting early flowering of long-day plants, regardless of intensity or duration.
The effects of supplemental light provided by high- and low-pressure sodium (HPS and LPS), metal halide (MH), and incandescent filament (INC) lamps were determined on the photomorphogenic responses of strawberry (Fragaria × ananassa Duch.) plants. Supplemental light was provided in the greenhouse under normal winter conditions of 9–12 hr of daylight in Beltsville, Md. Growth responses of representative Junebearer (‘Badgerbelle’), everbearer (‘Our Own’), and day-neutral (‘Tribute’) plants propagated by tissue culture (TC) and conventional means (RP) were recorded under supplemental lighting compared to natural day length (ND) conditions and with long days simulated by ND supplemented with a daily 4-hr night interruption (NI) with 0.9 W·m–2 (400–850 nm) INC exposure (ND and NI) at 2200–0200 hr. Vegetative and reproductive responses to supplemental lighting varied with the photoperiod class of the cultivar and with its mode of propagation. Vegetative growth (stolon and daughter plant development) of Junebearer RP and both Junebearer and everbearer TC plants was promoted by all supplemental light treatments. Supplemental light did not promote growth of everbearer RP plants or day-neutral TC or RP plants. Crown branching of day-neutral TC plants was promoted by several treatments, but the number of crowns on RP plants was increased only under LPS at 12 W·m–2 for 24 hr. Flower truss initiation of Junebearer plants was not stimulated by supplemental light treatments compared to ND. Everbearer RP plants produced more flower trusses under supplemental light treatments compared to ND, but TC plants were stimulated only by LPS at 12 and 24 W·m-2 for 24 hr. Day-neutral RP plants produced more flowers per truss under most treatments compared to ND, but TC plants produced the greatest number of flowers per truss under MH at 12 W·m-2 for 24 hr.
Marigold was grown on 4 media treatments with different levels of composted digested sewage sludge. On each medium, a number of fertilizer amendment treatments were studied to evaluate compost as a replacement for the amendments ordinarily required for complete media. Media contained 0, 33, 67, and 100% sludge compost (by volume); the remainder was unfertilized Cornell mix (equal volume mixture of sphagnum peat moss and vermiculite). The recommended amendments for Cornell mix (N, P, limestone, and trace elements) were deleted one at a time, all, or all but N. Severe P deficiency of −P media was fully corrected by compost at all rates. Compost provided only part of the N requirement at 33%. All trace element requirements were supplied by compost, yet toxicities did not occur; compost-amended media pH was ≥ 6.7, which limited metal availability to plants. Soluble salts limited yield somewhat on all treatments containing 67 or 100% compost. Fertilization of 33% compost media with only KNO3 (recommended rate for Cornell mix) allowed plant performance equal to the complete Cornell mix. Compost supplied much higher amounts of Fe, Zn, and Cu than are ordinarily added to media, and corrected an apparent marginal Cu deficiency-stress of complete Cornell mix. Composted digested sewage sludge was found to be an effective ingredient for potting media for marigolds when N is supplied from chemical sources.
Alkvlnaphthalenes are used as solvents for chlorinated insecticides and herbicides. Johnson, Veomans, and Smith (2) reported that these solvents could cause the death of the apical meristems of chrysanthemums when applied in concentrated solutions or in mechanically or thermallv generated aerosols. Controlling the number of flowers and fruits on a stem is not only of academic interest but of practical importance. Thev are now controlled on chrysanthemums by removing the excess by hand. Research reported in this paper show that HAN,R a petroleum fraction containing a large percentage of alkvlnaphthalenes. can be used to control the number of flowers borne by chrysanthemum plants.