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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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James L. Gibson and Brian E. Whipker

Vigorous osteospermum (Osteospermum ecklonis) cultivars Congo and Wildside received foliar sprays of daminozide or daminozide + chlormequat (Expt. 1). Both cultivars responded similarly to the plant growth regulator (PGR) treatments. Only a limited amount of plant height control occurred using 5,000 mg·L-1 (ppm) daminozide + 1,500 mg·L-1 chlormequat or 5,000 mg·L-1 daminozide + 3,000 mg·L-1 chlormequat. Flowering was delayed, phytotoxicity was observed, while peduncle length increased, suggesting that higher concentrations of daminozide or chlormequat may or not be effective at any concentration and may result in increased phytotoxicity. In Expt. 2, `Lusaka' received foliar sprays or substrate drenches of paclobutrazol or uniconazole. Foliar sprays ≤80 mg·L-1 paclobutrazol or ≤24 mg·L-1 uniconazole were ineffective in controlling plant growth. Substrate drenches of paclobutrazol (a.i.) at 8 to 16 mg/pot (28,350 mg = 1.0 oz) produced compact plants, but at a cost of $0.23 and $0.46/pot, respectively, would not be economically feasible for wholesale producers to use. Uniconazole drenches were effective in producing compact `Lusaka' osteospermum plants. Uniconazole drench concentrations of 0.125 to 0.25 mg/pot were recommended for retail growers, while wholesale growers that desire more compact plants should apply a 0.25 to 0.5 mg/pot drench. Applying uniconazole would cost $0.06 for a 0.25 mg drench or $0.12 for a 0.5 mg drench.

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Song Ping and Ellen B. Peffley

Callus of five onion genotypes representing two species. Allium cepa and A. fistulosum, and their interspecific hybrid were used for establishing suspension cultures. Cultures were derived from callus that had been maintained on solid media and routinely subcultured for four years and from callus induced within six months of this experiment. Long-term callus from which plants were routinely regenerated and newly-induced callus were composed of cells which were, for the most-part, meristem-like with higher mitotic indices than cells from long-term callus which had been maintained as callus but had lost us capability to regenerate plants, these cells were large with small nuclei. Callus from newly-induced and long-term regenerable cultures were selected for further studies. Eight liquid media with factorial combinations of plant growth regulators were tested. Cells cultured in BDS liquid medium supplemented with 0.5 mg/l ABA and 1.0 or 2.0 mg/l 2,4-D without e-BA had higher mitotic indices and plant regeneration percentages than did cells cultured in the same media without ABA and with 6-BA. Suspension cultures from A. fistulosum and interspecific hybrids with A. fistulosum produced the highest numbers of plants regenerated.

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Jianjun Chen, Russell D. Caldwell and Cynthia A. Robinson

Gynura aurantiaca is a colorful foliage plant with creeping stems and velvety purple hairs that cover the green leaves. It grows rapidly, but is cultivated primarily for those attractive purple leaves. Annually during the spring, this plant produces prominent flowers both in appearance and smell, gaudy and malodorous. Flowering coupled with acquiring an over-grown leggy appearance have been key limitations in its production and use in interiorscaping. This study was undertaken to determine if an available commercial plant growth regulator could inhibit flowering. A-Rest (ancymidol), B-Nine (daminozide), Bonzi (paclobutrazol), cycocel (chlormequat chloride) and florel (ethephon) each diluted to three different concentrations were sprayed in two applications in early spring at 2-week intervals. Flowering and bud numbers and plant growth (number of lateral shoots, vine lengths and internode lengths) were recorded. Results indicated that applications of A-Rest, B-Nine, Bonzi and Cycocel, regardless of treatment concentrations, were ineffective in suppressing the flowering of this plant; whereas, florel completely suppressed flowering at the three concentrations used. The florel-treated plants also grew more lateral shoots, which produced a compact and dense bush-look, indicating that appropriate concentrations of florel application not only will stop flowering of purple passion but can also improve and prolong its aesthetic value as a potted or hanging-basket interior plant.

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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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James L. Gibson and Brian E. Whipker

Ornamental cabbage and kale (Brassica oleracea var. acephala L.) plants of cultivars `Osaka White' and `Nagoya Red' were treated with paclobutrazol and uniconazole as foliar sprays or soil drenches. These treatments were compared to the industry standard of daminozide foliar sprays. Ten plant growth regulator (PGR) drench treatments (in mg a.i./pot) were applied 22 days after potting: paclobutrazol at 1 to 16 and uniconazole at 0.125 to 2. Thirteen PGR foliar sprays (in mg/L) were also applied: paclobutrazol at 5 to 80, uniconazole at 2 to 32, daminozide at 2500, 2500 (twice, with the second application occurring 14 days later), or 5000, and an untreated control. Applying drenches of paclobutrazol at 4 mg or uniconazole at 0.5 mg controlled height by 16 to 25%, but at the cost of $0.11 per pot would not be economically feasible for growers to use. Paclobutrazol foliar sprays at concentrations of up to 80 mg/L were ineffective in controlling plant height and diameter of either `Osaka White' or `Nagoya Red'. Uniconazole foliar sprays between 2 and 8 mg/L were effective in controlling height (by 19%) and diameter (by 15%) as daminozide foliar sprays of 2500 mg/L, sprayed twice, with a cost to the grower of $0.02 per pot.

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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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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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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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Bruce P. Bordelon and J.N. Moore

Plant growth regulators (PGRs) [antigibberellins (mepiquat chloride, uniconazole, ancymidol, daminozide, chlormequat, ethephon, methazole), cytokinins (BAP, kinetin, BTP, 2iP), and ABA] were evaluated at various concentrations and timings for promotion of seed trace development and germination of four stenospermic grape cultivars (Vitis spp.): `Venus', `Mars', `Reliance', and `Saturn'. Data include seed trace number per berry, percent of seed traces with endosperm (sinkers), sinker fresh weight, and percent seed trace germination. Several PGRs effectively increased seed number and percent sinkers over control treatments. PGRs had little effect on seed fresh weight and percent germination. PGRs promoted greater increases in percent sinkers than seed number on all cultivars. The number of viable seeds per sample (seed number × percent sinkers) was increased over controls by up to 802% on `Reliance', 239% on `Saturn', 154% on `Mars', and 153% on `Venus'. A moderate percentage of viable seeds from treatments and controls of `Mars', `Venus', and `Saturn' germinated and established normal seedlings. The very small seed traces of `Reliance' did not germinate from either controls or treatments. The results indicate that PGRs can stimulate seed trace formation in some stenospermic cultivars and therefore may be useful tools in grape breeding programs. Chemical names used: abscisic acid (+/-)cis-trans isomer (ABA); a-cyclopropyl-a-(4-methoxy-phenyl)-5-pyrimidinemethanol (ancymidol); 6-benzylaminopurine (BAP); 6-benzylamino-9-(2 tetra-hydropropanyl)-9H-purine (BTP); (2-chloroethyl) trimethyl-ammonium chloride (chlormequat); succinic acid 2,2 dimethyl-hydrazide (daminozide); (2-chloroethyl) phosphonic acid (ethephon); 6-(dimethyl-allylamino) purine (2iP); 6-furfurylaminopurine (kinetin); N,N-dimethyl-piperidinium chloride (mepiquat chloride); [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] (methazole); E-1-(4-chlorophenyl)-4,4-di-methyl-2-(1,2,4-triazol-1-yl)-1-pentan-3-ol (uniconazole).