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Mélanie Leclerc, Claude D. Caldwell, Rajasekaran R. Lada and Jeffrey Norrie

Field experiments were conducted in 2002 and 2003 to evaluate the effects of selected plant growth regulators on propagule production in Hemerocallis `Happy Returns' and Hosta `Gold Standard'. Benzyladenine (BA), chlormequat chloride (Cycocel), ethephon (Ethrel), prohexadione calcium (Apogee), and an experimental preparation of commercial seaweed extract (Acadian Seaplants Limited Liquid Seaweed Concentrate) amended with BA and IBA were tested at two times of application and three rates of application. Results with Hemerocallis showed that the application of the seaweed/PGR mixture at 3000 mg·L–1, Cycocel at 3000 mg·L–1 or BA at 2500 mg·L–1 applied at flowering, increased the number of plants producing two divisions compared to control plants. In Hosta, no increase in divisions under any treatments was observed.

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J. Pablo Morales-Payan

Field studies were conducted in the Dominican Republic to determine the effect of several plant growth regulators on the yield of `Jira' eggplant. Treatments consisted of aqueous solutions of folcysteine (25, 50, 75 ppm), giberellic acid 3 (10, 20, 30 ppm), kinetine (25, 50, 75 ppm), naphthalenacetic acid (NAA) (25, 50, 75 ppm), 2,3,4-dichloro-phenoxy-triethyl-amine hydrochloride (DCPTA) (25, 50, 75 ppm), triacontanol (5, 10, 15 ppm), ethanol (5, 10, 15%), and chlormequat (50, 100, 150 ppm) sprayed at early flowering, directed to the crop upper leaves and flowers. A control treatment (no plant growth regulators applied) was also included. A randomized complete-block design with four replications was utilized. Experimental units were two rows of 10 plants at a 1.0 × 0.4-m distancing. Eggplant fruit set and yield were determined after 10 harvests performed at 3-day intervals. Analysis of variance and mean comparison tests were performed on the resulting data. `Jira' eggplant fruit set and yield was significantly improved by folcysteine, giberellic acid 3, and NAA, but not by kinetine, DCPTA, ethanol, triacontanol, or chlormequat. Eggplant yield increased as folcysteine rate increased from 0 to 50 ppm, but no further yield increase was obtained when increasing the rate from 50 to 75 ppm. Similarly, eggplant yield significantly increased as gibberellic acid increased from 0 to 20 ppm, but not when rates increased from 20 to 30 ppm. With NAA, eggplant fruit set and yield significantly increased above that of control plants when 25 ppm was applied, with no significant yield increase at higher rates. Results indicate that the yield of `Jira' eggplants could be enhanced by the treatments with either folcysteine, NAA, or gibberellic acid hereby described.

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Guochen Yang and P. E. Read

Vanhoutte's spiraea has been propagated in vitro using explants from softwood growth of dormant stems forced in a solution containing 200 mg/l 8-hydroxyquinoline citrate (8-HQC) and 2% sucrose (Yang and Read, 1989). Objectives to further utilize this system were to determine the feasibility of applying plant growth regulators (PGR) via the forcing solution to softwood growth from forced dormant stems and to study the resulting influence on in vitro culture. BA and GA3 were placed in the forcing solution at various concentrations, including a zero PGR control. Explants were cultured on Linsmaier and Skoog (LS) medium containing zero PGR or different amounts of BA or thidiazuron (TDZ) or combinations of BA and IAA. Control explants placed on LS medium supplemented with 5uM BA with or without 1 or 5uM IAA, or with 0.5 or 0.75 uM TDZ alone produced the best shoot proliferation. BA in the forcing solution stimulated micropropagation, while GA3 caused less proliferation than explants from control solutions. Forcing solutions containing PGR are useful for manipulating responses of plant tissues cultured in vitro and for studying PGR influence on woody plant physiology.

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Guochen Yang and Paul E. Read

A forcing solution containing 200 mg 8-hydroxyquinoline citrate per liter and 2% sucrose has been demonstrated to extend the season for obtaining softwood growth suitable for use as explants in micropropagation (Yang & Read 1989). Forcing dormant woody stems in the off-season in this fashion also enhances the macropropagation of woody plant species by providing softwood outgrowth that can be rooted as softwood cuttings. GA3, IBA, IAA and NAA were incorporated into softwood growth which was later used as cuttings for rooting by adding plant growth regulators at various concentrations to the forcing solution. GA3 incorporated into the forcing solution hastened bud break, increased shoot elongation, but inhibited rooting of softwood cuttings taken from stems forced in this manner. IBA, IAA and NAA in the forcing solution exhibited typical auxin effects on rooting of cuttings by increasing root number per cutting and root elongation. In order to expedite macropropagation of woody plants, GA3 and IBA were added SEQUENTIALLY to the forcing solution. Addition of IBA to fresh forcing solution following initial use of GA3 in the forcing solution counteracted the negative effects of GA3 and stimulated rooting. This protocol is proposed as a method to assist propagation in rooting difficult species by softwood cuttings in the off-season.

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H. Yakushiji, K. Morinaga and Y. Koshita

The effects of 2,3,5-triiodobenzoic acid (TIBA) and naphthaleneacetic acid (NAA) on berry maturation and photoassimilates partitioning were investigated. Five-year-old potted `Kyoho' grape grown under a non-heating glasshouse were used. TIBA (200 mg/L) and NAA (200 mg/L) were applied to clusters at the beginning of veraison (45 days after full bloom). TIBA application increased not only soluble solids concentration in the juice but also anthocyanin content of peel, compared with those of control. On the other hand, the application of NAA reduced berry growth and delayed the berry maturation with harder flesh, lower soluble solids, higher acidity and poor coloration. In order to examine the effect of both plant growth regulators on photoassimilates partitioning in plant tissues, the whole plants were fed with 13CO2 at 10 days and 20 days after application of TIBA and NAA. The 13C distribution of pericarp and peel in NAA application was found on the lowest among the treatments. However, there were no significant differences in the 13C distribution and 13C absorption rate of pericarps between TIBA and control. These results indicate that NAA weakened the sink activity in grape berries, resulted in smaller berry size and the delay of maturation, whereas the berry ripening induced by TIBA application could not be explained by the distribution of photoassimilates in grape berries.

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Wayne L. Schrader

Artichoke is a cool-season perennial crop that is grown as an annual from seed in southern California. Growing artichokes as annuals from seed allows growers to harvest during the winter from November to March. Artichoke seed is planted in May, transplants are moved to the field in July, and harvesting begins as early as November in years with relatively cool fall weather. Hot fall weather during September and October suppresses plant growth and causes premature flowering, which lowers yield and average bud size. Plant growth regulator (PGR) treatments were evaluated in annual artichokes to determine if they could reduce the adverse effects of hot weather during September and October. Treatments included multiple applications of apogee (gibberellin inhibitor), retain (ethylene inhibitor), apogee + retain, cytokinin, and control plots. Harvestable buds were counted as a measure of earlier flowering induced by hot weather. Apogee and cytokinin show promise in reducing heat stress during hot fall artichoke production. Other PGR treatments increased the number of harvestable buds compared to control plots.

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Bruce P. Bordelon and J.N. Moore

Various plant growth regulators were used to stimulate endosperm and embryo development in four stenospermic grape cultivars. Five antigibberellins were applied to clusters at 1000 and 100 ppm two weeks prior to bloom. Two cytokinins were applied at 1000, 500, and 250 ppm 20 days after bloom. Combinations of the treatments were also made. Data collected included: 1) cluster weight, 2) berry weight, 3) number of `sinker' and `floater' seed traces, 4) `sinker' weight and 5) percent germination. Significant differences were found among treatments for some of the variables. Differences also occurred among cultivars. Percent germination was greater for cultivars with large seed traces. The technique appears to have promise as an alternative to ovule culture/embryo rescue for intercrossing stenospermic grapes.

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Xunzhong Zhang, R.E. Schmidt, E.H. Ervin and S. Doak

Creeping bentgrass (Agrostis palustris Huds.) is an extensively used cool-season grass for fine turf areas such as golf course putting greens, but suffers from poor summer stress tolerance. These studies were conducted to investigate the influences of natural plant growth regulators (NPGR) and Fe on creeping bentgrass photochemical activity (PA), antioxidant superoxide dismutase (SOD) activity, root growth and leaf color under two fertilization regimes. The bentgrass was maintained in well-watered field conditions or water-stressed glasshouse conditions. A mature bentgrass was treated monthly during the field season with seaweed (Ascophyllum nodosum Jol.) extract (SWE) at 50 mg·m-2 or humic acid (HA) at 150 mg·m-2 or in combination with or without FeSO4 at 520 mg·m-2 and grown under a low or a high fertilization regime. Foliar application of SWE + Fe increased PA (14% to 15%), while applications of SWE + HA or SWE + HA + Fe increased SOD activity (49% to 114%) of creeping bentgrass in Summer 1997 and Summer 1998. There was no significant fertilization × NPGR interaction for PA and SOD activity. Bentgrass PA was increased by 13% to 46% when treated with NPGR with or without Fe compared to the control measured in May. The addition of Fe with each NPGR application improved fall and winter leaf color. All NPGR and Fe treatments increased root mass (17% to 29%) in Aug. 1997 and 1998, except HA alone in 1998. Under sustained low soil moisture (-0.5 MPa) conditions, application of NPGR with or without Fe increased PA and SOD activity. The data indicate that SWE and HA enhance the physiological function of `Southshore' creeping bentgrass, resulting in improved root growth regardless of low or high fertilization regime. However, addition of Fe to these NPGR served primarily to improve late season leaf color. The results suggest that, in addition to maintaining adequate plant-available nutrients, applications of natural PGRs, such as SWE and HA, prior to and during summer abiotic stresses would be beneficial.

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Matthew J. Fagerness, John Isgrigg III, Richard J. Cooper and Fred H. Yelverton

Questions exist as to whether growth-inhibiting chemicals mimic the effects of reduced mowing heights on putting green ball roll. An experiment was initiated during Spring 1997 to investigate ball roll and visual quality parameters of putting greens maintained at 3.2, 4.0, or 4.8 mm with plant growth regulator (PGR) treatments applied monthly over the course of 1 year. Additional experiments were conducted during Fall 1995 and 1996 and Spring 1996 to investigate diurnal PGR effects on ball roll. All experiments were conducted on pure stands of `Penncross' creeping bentgrass (Agrostis palustris Huds). Treatments included trinexapac-ethyl and paclobutrazol, both inhibitors of gibberellin biosynthesis. In the one-year experiment, mowing height was inversely related to ball roll. However, compromises in turfgrass visual quality and shoot density in `Penncross' turf mowed at 3.2 mm make this a questionable mowing height in areas with severe summer conditions. Ball roll during summer months was reduced by PGRs, suggesting that PGRs have little potential as alternatives to decreasing mowing height for increased ball roll. Paclobutrazol reduced turfgrass quality and shoot density during summer months, suggesting that it be used with caution. Other PGRs, particularly trinexapac-ethyl at 0.05 kg·ha–1 a.i., increased afternoon ball roll by as much as 5% to 10% in diurnal experiments. Use of PGRs on creeping bentgrass putting greens may therefore produce short-lived increases in ball roll with subtle to negative effects on bentgrass growth over more extended periods of time. Chemical names used: 4-(cyclopropyl-α-hydroxymethylene)-3,5-dioxocyclohexane carboxylic acid ethylester (trinexapac-ethyl); (+/–)-(R *,R *)-β-[(4-chloro-phenyl)methyl]-α-(1,1dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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Sushobitbir Singh Thind, Harmander Pal Singh and Sukhdev Singh

Peach [Prunus persica Batsch. (L.)] is a major fruit of northern India, which is commercially propagated through stem cuttings. There is a scarcity of information available on the effect of plant growth regulators (PGRs) and time of plantings on rooting of peach stem cuttings. Studies were conducted to learn the effects of various PGRs and planting times on stem cuttings of peach cv. Shan-i-Punjab at the fruit nursery of the Horticulture Department, Khalsa College, Amritsar, India, in 2001 and 2002. The study on stem cuttings, taken from the middle portion of the shoot, compared three PGRs: indolebutyric acid (IBA), indoleacetic acid (IAA), and naphthaleneacetic acid (NAA), each at concentrations of 50, 100, and 200 mg·L-1 and two planting dates (20 Dec. and 20 Jan.). Cuttings were treated for 24 hours before keeping under moist sand for 1 month for callusing. Callused cuttings were planted in the field. Measurements on sprouting percentage, survival percentage, plant height, shoot diameter, number of leaves per plant, leaf size, average root length, and root weight per cutting were recorded. The study showed that, overall, auxins had significant effect on the success and rooting character of peach plants over the control. The greatest sprouting and survival percentage, plant height, leaf area, and shoot diameter was exhibited by IBA followed by IAA and NAA. IBA at 100 ppm proved to be the most suitable PGR for improving success along with other rooting and vegetative characters of the plant. The cuttings planted on 20 Dec. gave a higher percentage of success (55.32%) over those planted on 20 Jan. (33.04 %), during both years of study. The other plant characteristics, such as average root length, plant height, leaf area, and plant height, of cuttings planted on 20 Dec. also showed greater success during both years.