HORTSCIENCE VOL. 40(2) APRIL 2005 404 Multivariate Repeated Measures Analysis of Plant Growth Regulators on Tradescantia virginiana Sarah A. White, 1 Holly L. Scoggins, 2 Richard P. Marini, 3 and Joyce G. Latimer 4 Department of Horticulture, Virginia Tech, Blacksburg, VA, 24060 Additional index words. spiderwort, plant growth regulators, herbaceous perennials, Topflor, Bonzi, Sumagic, repeated measures Abstract. Little information is available on cultural requirements for greenhouse production of Tradescantia virginiana L. We tested three plant growth regulators (PGRs) at ascend- ing rates on T. virginiana ‘Angel Eyes,’ ‘Blue Stone,’ and ‘Red Cloud’ in an effort to find appropriate application levels for height suppression. Treatments applied two weeks after transplant. Each PGR was applied once at the following rates: paclobutrazol at 0, 40, 80, 120, or 160 mg⋅L –1 , uniconazole at 0, 15, 30, 45, or 60 mg⋅L –1 , or flurprimidol at 0, 15, 30, 45, 60, or 75 mg⋅L –1 . Repeated measures experimental design and multivariate analysis was used to examine plant responses to PGRs over time. The most effective paclobutrazol rate for adequate height suppression was 120 mg⋅L –1 . Uniconazole at 30 to 45 mg⋅L –1 and flurprimidol at 45 to 60 mg⋅L –1 resulted in adequate height control. ‘Blue Stone’ and ‘Red Cloud’ appeared more responsive (greater suppression of height at rates applied) to both uniconazole and flurprimidol than ‘Angel Eyes.’ These results suggest that cultivars respond in a different manner to PGRs applied to them; more compact growth can be obtained for cultivars tested using these suggested rates. Chemical names used: trifuloromethoxy phenyl-5-pyrimidinemethanol (flurprimidol); [(±)-(R*,R*)-ß-((4-chlorophenyl) methyl)-?- (1,1,-dimethylethyl)-1H-1,2,4,-triazole-1-ethanol)] (paclobutrazol); uniconazole. Tradescantia virginiana (spiderwort) is an herbaceous perennial native to eastern and central North America. As a garden plant, it has proved well adapted to sun and shade as well as both wet and dry areas. These characteristics, along with the numerous cultivars available and extended flowering period during the sum- mer, make them good landscape plants. In the landscape, the vigorous and spreading growth habit of spiderwort is desirable, but container production can be a challenge. Foliage often outgrows the pot and becomes unsightly and lodges. This characteristic, especially notice- able late in the summer season, reduces crop marketability. A method of temporarily sup- pressing vegetative growth in the greenhouse or nursery, before retail sale, would improve the appearance of the plants and possibly enhance sales. Little information is available concerning the cultural requirements of T. virginiana. No published research exists on use of plant growth regulators (PGRs) on spiderwort. Flurprimidol (FLU), paclobutrazol (PAC), and uniconazole (UNI) are PGRs that control plant growth by inhibiting the synthesis of gibberellins and their effects on ornamental plants have been examined in numerous studies. Response to application of PGRs is dependent upon the species. Plant height may be suppressed with or without bloom delay. Pobudkiewicz and Nowak (1994) studied Dian- thus caryophyllus L. ‘Snowmass’ and obtained desirable height control with no reduction in flower size or number with foliar applications of 15 and 22.5 mg⋅L –1 FLU. Consistent suppres- sion of vegetative and flower stalk growth of Canna ×generalis L.H. Bail. ‘Florence Vaughn’ was attained with foliar application of FLU at 50 mg⋅L –1 , but the suppression of flower stalk growth greatly reduced the salability of the plant (Bruner et al., 2000). Buddleia davidii Franch. ‘Royal Red’ treated with FLU as a foliar spray at 62.5 mg⋅L –1 had suppressed shoot growth over a short time without any delay in flowering (Keever and Gilliam, 1994). Foliar applications of paclobutrazol at rates of 25 or 100 mg⋅L –1 to Verbena rigida Spreng. suppressed plant height without af- fecting time to flower (Davis and Andersen, 1989). Dutch-grown bleeding hearts [Dicentra spectabilis (L.) Lem.] had delayed flowering with PAC foliar application at 50 mg⋅L –1 ; however, treatment resulted in darker green coloration of the leaves and adequate height control (Kim et al., 1999). Foliar UNI appli- cation at 15 mg⋅L –1 to Oenothera fruticosa L. resulted in a 31% reduction in plant height at flowering compared with controls and flower diameter was reduced by 36% (Clough et al., 2001). Gibson and Whipker (2001) reported that increasing the concentrations of UNI (2, 4, 8, 16, or 32 mg⋅L –1 ) foliar sprays reduced plant height in a linear manner for both ‘Osaka White’ and ‘Nagoya Red’ ornamental cabbage (Brassica oleracea var. acephala L.). Researchers in tree fruits, forestry, and other fields requiring long-term measurements frequently use repeated measures analysis of variance to compare responses of the same ex- perimental unit over time or space (Fernandez, 1991). Plant growth regulator studies on her- baceous ornamentals often use a point-in-time general linear model (GLM) analysis. Most of these experiments are relatively short-term, and these analyses provide comparisons among treatments at a certain point—market-ready, anthesis, or some other event. An exception is described by Littell (1989) in his discus- sion of PGR work on chrysanthemum. In this case, the use of repeated measures analysis revealed differences in PGR effects depending on the rate of growth (fast vs. slow). The main advantage of the repeated measures design is that it controls for subject heterogeneity, that is, individual differences. There are benefits of taking into account the initial or previous measurement (e.g., height) as a factor, though this results in a more complicated covariance structure (Littell et al., 1998). But recent ad- vances in statistical methods make for efficient and effective analysis of data. One method is to use the REPEATED statement of SAS’s general linear model (GLM) procedure (SAS Institute Inc., Cary, N.C.). Even short-term studies on nursery and greenhouse crops such as this one can benefit from examination of response trends over time. This study examines the effect of PAC, UNI, and FLU on height, width, and flowering of T. virginiana plants as measured over time. Materials and Methods The experiments were conducted in a double-layer polyethylene-covered house (25 Mar. to 20 May 2002). Preliminary screenings revealed rapid spring growth of T. virginiana with flowering plants of marketable size produced from liners in <6 weeks (data not shown). Three cultivars of T. virginiana were used in this experiment: Blue Stone, Angel Eyes, and Red Cloud (54 cell size; Yoder Greenleaf Perennials, Leola, Pa.). One hundred vernalized liners per cultivar were planted each in 10.8-cm-diameter (1180 cm 3 ) plastic containers using media containing: 65% to 75% bark fines, 20% to 25% Canadian sphagnum peatmoss, 9% to 15% perlite and a proprietary starter charge (Sierra Perennial Mix, Scott’s Co., Merrifield, Ohio) on 11 Mar. 2001. Throughout the experiment, irrigation and fertilizer (15N–6.9P–14.1K at 200 mg·L –1 nitrogen, applied as constant liquid feed) was applied to the entire study at an equal volume (350 mL/pot) at each irrigation. Three days before PGR application, 88 uniform plants per cultivar were selected. Each PGR was considered to be an experiment. We used a factorial treatment design of three cultivars × five or six rates of PGRs. The experimental design was a randomized complete block with HORTSCIENCE 40(2):404–408. 2005. Received for publication 2 Aug. 2004. Accepted for publication 4 Oct. 2004. Use of trade names does not imply endorsement of named products nor criticism of similar ones not named. acknowledged. This paper is from a thesis submitted by the senior author in partial fulfillment of the requirements for the MS degree. The authors gratefully acknowledge the technical assistance of Velva Groover. Plant material generously provided by Yoder Green Leaf, Lancaster, Pa. Multivariate repeated measures analysis of plant growth regulators on Tradescantia virginiana. 1 Former graduate student, currently graduate research assistant in the Biological Sciences Department, Clemson University, Clemson, SC 29634. 2 Assistant professor; e-mail hollysco@vt.edu. 3 Professor. Current address: Pennsylvania State University, University Park, PA 16802. 4 Professor.