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Jacob George, Harsh Pal Bais, G.A. Ravishankar, and P. Manilal

Response surface methodology was utilized in statistical optimization of three quality factors (the number of multiple shoots, shoot length, and number of leaves) pertaining to regeneration of plantlets from leaf calli of Decalepis hamiltonii Wight. & Arn. (swallow root). The variables evaluated were the levels of sucrose, BA, and NAA each at two different concentrations. Response surfaces for shoot length and multiple shoot number were useful in achieving optimal levels of media constituents and in understanding their interactions, but response surfaces for number of leaves were not. The data indicate that sucrose, BA, and NAA levels may be manipulated to increase or decrease quality factors chosen. This approach may be useful in developing a micropropagation protocol for D. hamiltonii. Chemical names used: benzyladenine (BA); napthaleneacetic acid (NAA).

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James R. Schupp and Duane W. Greene

To compare the effects of growth regulators on preharvest fruit drop and fruit maturity, aminoethoxyvinylglycine (AVG) was applied to `McIntosh' apple trees at 75, 150, or 225 mg·L-1, at 8, 4, or 2 weeks before harvest (WBH). These treatments were compared to NAA, daminozide, and to an untreated control. All AVG treatments and timings except 75 mg·L-1 applied 8 WBH delayed preharvest drop and fruit maturity. AVG applied at 225 mg·L-1was more effective in delaying drop and development of maturity than other rates when applied 8 or 2 WBH, but at 4 WBH, 150 mg·L-1 gave equivalent results to 225 mg·L-1. AVG at 150 mg·L-1 was superior to NAA or daminozide as a stop-drop agent. No concentration, or time of application of AVG influenced fruit size at harvest. AVG reduced internal ethylene concentration (IEC) in `McIntosh' apples linearly with increasing AVG concentration. There was a linear relationship between time of AVG application (8, 4, or 2 WBH) and IEC in the fruit after harvest, and the time required for harvested fruit to enter the ethylene climacteric. Development of red color was delayed by AVG. This was attributed to a delay in ripening as determined by a slower increase in IEC and starch hydrolysis. In general, earlier application of AVG resulted in reduced effectiveness of lowering IEC following harvest. Chemical names used: aminoethoxyvinylglycine (AVG), naphthaleneacetic acid (NAA), succinic acid-2,2-dimethylhydrazide (daminozide).

Open access

Rachel Leisso, Bridgid Jarrett, and Zachariah Miller

aminoethoxyvinylglycine [AVG ( Layne et al., 2002 )] and affecting abscission physiology via a synthetic auxin, 1-napthaleneacetic acid [1-NAA ( Nartvaranant, 2018 )]. The objectives of our 2020 haskap field trials were to record PHFD rates among haskap cultivars

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Fumiomi Takeda

NAA at 0.25% to 1.0% applied in late May on the basal portion of thornless blackberry (Rubus, subgenus Eubatus) primocanes inhibited lateral shoot growth in the treated area and reduced the number of primocanes. However, regrowth occurred near or below ground from axillary buds not contacted by NAA. Rates of (0.25% and 0.12570 NAA did not affect the terminal or lateral growth above the treated area. The reduced number of basal lateral shoots facilitated machine harvesting. Chemical name used: napthaleneacetic acid (NAA).

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Jean-Marc G. Guedon* and James McConnell

Elaeocarpus yoga Merr. (Tiliaceae) is an attractive tree indigenous to the Mariana Islands and Palau. Recently its population has declined due to deforestation, typhoon damage, and pest problems. Stem cuttings of E. yoga were taken from hardwood, semihardwood, or softwood and treated with acid or salt forms of indole-3-butyric acid (IBA) or napthaleneacetic acid (NAA) at several concentrations. The cuttings were treated with on of the following: acid form at 0.5 mL·L-1 IBA + 0.25 mL·L-1 NAA; 1 mL·L-1 IBA + 0.5 mL·L-1 NAA, 2 mL·L-1 IBA + 1 mL·L-1 NAA; salt form at 1, 3, and 8 g·kg-1 IBA/. Rooting after 8 weeks was compared among treatments. The salt form of the IBA treatment at 3 g·kg-1 produced the greatest rooting percentage, root number and length. The acid form containing both IBA and NAA produced the smallest average rooting percentage.

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Michelle Carratu and Roger J. Sauve

Several studies were conducted to evaluate the effects of cultivar, cutting length, and leaf number on rooting of poinsettia. Cuttings were rooted under mist in a soilless medium with 50 cuttings per treatment. Visual rootball ratings were performed after 3 wk. In the first experiment, rooting of ten poinsettia cultivars was compared. The rooting hormone was 0.1% indole-3-butyric acid (IBA). Rooting of `V-14 Red' and `V-14 Marble' was the highest. `V-17 Pink' and `V-17 Marble' had the highest number of callused cuttings. `V-17 White' produced the highest number of extensively rooted cuttings. `V-14 Pink' (3-lf) cuttings 12 cm long rooted better than 5 cm cuttings. Rooting of (7 cm) 3- and 4-leaf cuttings was higher than rooting of 2-leaf cuttings. `V-14 Pink' cuttings treated with 0.8% IBA or 1% IBA + 0.5% 1-napthaleneacetic acid (NAA) rooted better than with 0.1% or 0.3% IBA.

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Paula P. Chee

Plant regeneration from tissue cultures of summer squash (Cucurbita pepo L. ev. YC60) has been observed. Embryogenic callus tissues were initiated when cotyledons of mature seeds were excised and cultured on Murashige and Skoog (MS) medium supplemented with either 22.7 μm 2,4-D or a combination of 4.7 μm 2,4,5-T, 4 μm BA, and 0.5 μm kinetin. Clusters of somatic embryos were found in callus tissue. Maturation of these somatic embryos was effected by transfer of embryogenic callus tissues to MS supplemented with 0.5 μm NAA and 0.25 μm kinetin. Regenerated mature plants were morphologically normal and set fruits containing seeds that germinated normally. Chemical names used: 6-benzylaminopurine (BA); 2,4-dichlorophenoxyacetic acid (2,4-D); α - napthaleneacetic acid (NAA); 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).

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Robert L. Geneve, Wesley P. Hackett, and Bert T. Swanson

Exogenous ethylene could not substitute for NAA to induce adventitious root initiation in juvenile petiole explants of English ivy (Hedera helix L.), indicating that the action of auxin-stimulated root initiation was not directly mediated through ethylene production. Mature petioles did not initiate roots under any auxin or ethylene treatment combination. Ethephon or ACC supplied at 50 or 100 μm was inhibitory to NAA-induced root initiation in juvenile petioles. The pattern of ethylene production stimulated by NAA application was significantly different in juvenile and mature petioles. Ethylene evolution by juvenile petioles declined to near control levels during from 6 to 12 days after NAA application. Reduction in ethylene production was due to reduced availability of ACC in juvenile petioles. Mature petioles continued to produce ethylene at elevated levels throughout the course of the experiment. Ethylene does not appear to play a significant role in the differential root initiation response of juvenile and mature petioles treated with NAA. However, ethylene appeared to have an inhibitory effect during root elongation stages of adventitious root development in juvenile petioles. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); 1-napthaleneacetic acid (NAA); 2-chloroethylphosphonic acid (ethephon).

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Mushtaq Sarwar and Robert M. Skirvin

Adventitious shoots were regenerated from apple (`Wijcik', `McIntosh', `Macspur', `M-26' and `Mutsu') by excising leaves from in vitro-grown shoots, cutting them into three sections, and plating them onto regeneration media. Cultures were kept in the dark for 1 to 4 weeks and then moved to light for further shoot development. MS medium supplemented with thiadiazuron (2-3 μM) and napthaleneacetic acid (5 μM) produced the highest number of shoots per leaf segment. `Wijcik' and `M-26' regenerated best from big leaves, whereas `McIntosh' and `Macspur' regenerated best from small leaves. Shoot formation was enhanced by 3 to 4 weeks of dark treatment and by placing the leaf on medium with its abaxial surface uppermost. The cut surface of leaf segments produced the most regeneration sites. In vitro adventitious shoots were transferred to various concentrations of BA (5, 10, 15, 20, 25 and 30 μM to screen them for BA tolerance and to predict their adult growth habit. These shoots will be rooted and transferred to greenhouse and field conditions for long-term evaluations.

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James R. Schupp and Highmoor Farm

Mature `McIntosh'/MM.111 apple (Malus domestica, Borkh.) trees were treated to evaluate the response of root pruned trees to chemical thinning and to determine if reducing the crop load increased fruit size on root pruned trees. The trees were root pruned at full bloom in 1988 and 1989, by cutting on both sides of the row 1m from the trunk and 30cm deep. Water, 600mg/liter carbaryl, 5mg/liter napthaleneacetic acid (NAA), or NAA plus carbaryl were applied when fruit diameter was approximately 10mm. Trunk cross-sectional area (TCSA) was increased by thinning treatments in 1988, but root pruning had no effect. In 1989, root pruning reduced TCSA increment by 35%. Shoot length was reduced by root pruning both years. All treatments reduced percent fruit set in 1989, however root pruned trees and trees treated with NAA had the highest fruit numbers at harvest. Preharvest fruit drop was reduced by root pruning in both 1988 and 1989. Root pruning had no influence on the response of apple trees to chemical thinning. Removing a portion of the crop with chemical thinners was partially successful in counteracting the reduction in fruit size caused by root pruning.