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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.

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Charleson R Poovaiah, Stephen C Weller, and Matthew A Jenks

An in vitro shoot regeneration procedure was developed for native spearmint (Mentha spicata L.) using internodal explants. Shoot regeneration from internodes was evaluated on Murashige and Skoog (MS) media supplemented with individual cytokinins thidiazuron (TDZ), benzylaminopurine (BA), kinetin (KT), or zeatin (ZT) or various pair wise combinations of these. The highest regeneration was achieved by the second internode on a medium containing MS basal salts, B5 vitamins, 10% coconut water, 1.0 mg·L–1 TDZ, 2.5 mg·L–1 ZT, and solidified with 0.2% phytagel. Unlike previous protocols this medium does not need sub culturing and produces elongated shoots in 4 weeks, rather than 6 weeks. Maximum number of shoots (36 per explant after 4 weeks) was observed when internodes from 2-week-old stock plants were used as explant source. The shoots were removed and roots were initiated on medium containing MS basal salts, 0.4 mg·L–1 thiamine-HCL, 100 mg·L–1 myo-inositol, 7.5 g·L–1 agar and 0.01 mg·L–1 ∝-napthaleneacetic acid (NAA) and then plants were transferred to the greenhouse 2 weeks after root initiation, where 100% of the plantlets developed into healthy plants.

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Sitheswary Logendra, Mei-Mann Hsueh, and Harry W. Janes

The effect of root mass on tomato fruit size in tissue culture was studied. The root mass of the ovaries was changed either by growing in culture media containing different concentrations of NAA (α– napthaleneacetic acid) or by culturing the ovaries with and without sepals. The root mass increased with a decrease in NAA concentration from 10.0 to 2.5 μM and the ovaries with sepals developed more roots. The tomato fruit size was affected by the root mass. The greater the root mass, the larger was the fruit size. However, the larger fruit size from ovaries cultured with sepals could be attributed either to the presence of more roots (greater absorption of sucrose) or to the sepal (additional carbon fixation by photosynthesis), or to both the sepals and more roots. Moreover, it is possible that the presence of sepals induce root development. These results indicate that the presence of sepals and total root mass are two important factors that influence the fruit size in vitro.

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Terence Robinson

Field thinning studies were conducted in two orchards at Geneva and Milton, N.Y., over 3 years (2003–05) using mature Gala/M.9 trees. A range of final croploads was achieved with various chemical thinning treatments, including, benzyladenine combined with carbaryl, or napthaleneacetic acid combined with carbaryl. The most-aggressive thinning treatments in the year with high rainfall achieved an average fruit size of 190–200 g; however, the yield was reduced considerably, resulting in a reduced farm gate crop value compared to less-aggressive thinning. In a dry year, the fruit sizes were smaller even with aggressive thinning. The optimum yield for maximum crop value varied for each orchard block for each year. The optimum croploads varied less than the optimum yield, since cropload normalizes the tree size between blocks. Optimum fruit size to maximize crop value varied narrowly between 155–170 g (113–100 count size) across blocks and years. This was true despite a substantial price difference between large, 80-count fruits and the moderate-size 113-count fruits. If lower prices received for processed apples were used in the analysis, then the optimum yield was significantly higher than with fresh fruit prices. In New York State, it appears that achieving 80-count fruit requires too large of a reduction in yield, which causes a reduction in crop value.

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Dennis Y. Yeo and Barbara M. Reed

Explants of three rootstock selections Pyrus calleryana Dcne `Oregon Pear Rootstock (OPR) 157', P. betulifolia Bunge `OPR 260', and P. communis L. `Old Home' × `Farmingdale 230' (`OH × F 230') were initiated from forced branches of field-grown trees. `OPR 260' and `OH × F 230' shoots cultured on Cheng medium with IBA proliferated better than those on NAA. NAA and IBA at concentrations >0.5 μm inhibited shoot multiplication. Overall, the best micropropagation medium for `OPR 260' and `OH × F 230' was Cheng medium with 8 μm BA and 0.5 μm IBA. Shoot multiplication of `OPR 157' was best on 8 μm BA and better on low NAA (0.5 μm) or no auxin than on IBA. `OH × F 230' rooted easily (>80%) with all IBA and NAA treatments. The best rooting treatment (42.9%) for `OPR 260' was 10 μm IBA in darkness for 1 week; for `OPR 157' (23.9%), it was a 15-second dip in 10 mm NAA. Only rooted plantlets survived 4 weeks of greenhouse acclimatization. Chemical names used: N6-benzyladenine (BA); indole-3-butyric acid (IBA); napthaleneacetic acid (NAA).

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Les Frey and Jules Janick

Shoot regeneration in carnation (Dianthus catyophyllus L.) was influenced by genotype, explant source, and plant growth regulator balance. Plants were regenerated from petals, calyxes, nodes, internodes, and leaves, but only petals, calyxes, and nodes were regenerative from all three cultivars examined (`Scania', `Improved White Sire', `Sandra'). Maximum proliferation was achieved with petals on Murashige and Skoog medium supplemented with 0.05 μm TDZ and 0.5 μm NAA. Shoot initiation originated from cells near vascular regions and perhaps from epidermal cells in petals and via organogenic callus from other explants. There was no evidence of chimeral separation from petals or callus, but somaclonal variants (3.3%) were observed involving petal hue and plant dwarfness. Unstable color patterns were observed in tissue-cultured regenerants of `Scania' and `Improved White Sire' similar in type and frequency to propagules derived from cuttings; none were observed for tissue-cultured or cutting-derived plants of `Sandra'. Chemical names used: N-pheny1-N′-l,2,3 -thiadiazol-5-ylurea [thidiazuron (TDZ)]; 1-napthaleneacetic acid (NM).

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Paul T. Wismer, J.T.A. Proctor, and D.C. Elfving

Benzyladenine (BA), carbaryl (CB), daminozide (DM), and naphthaleneacetic acid (NAA) were applied postbloom as fruitlet thinning agents to mature `Empire' apple (Malus domestica Borkh.) trees. BA, NAA, and CB reduced fruit set and yield per tree, and increased fruit size, percent dry weight, soluble solidscontent and return bloom. Fruit size was reduced, return bloom, length: diameter ratio and flesh firmness were increased, and fruit set and yield unaltered by DM. Although fruit set and yield were similar for BA, NAA, and CB, BA treated fruit were larger, indicating that BA increased fruit size beyond the effect attributable to chemical thinning alone. BA increased the rate of cell layer formation in the fruit cortex, indicating that BA stimulated cortical cell division. NAA, CB and DM had no effect on cell division rate. Mean cortical cell diameter at harvest was increased by NAA and CB and reduced by DM. Cell diameter at harvest in BA-treated fruit was similar to the control. These data support the hypothesis that BA-induced fruit size increase in `Empire' apple results from greater numbers of cells in the fruit cortex, whereas the fruit size increase due to NAA or CB is a consequence of larger cell size. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; 1-napthaleneacetic acid (NM); 1-naphthalenyl methylcarbamate [carbaryl (CB)]; butanedioic acid mono (2,2dimethyl hydrazide) [daminozide (DM)].

Open access

H.C. Wien, A.D. Turner, and S.F. Yang


A series of field and greenhouse experiments was conducted with three cultivars of bell pepper (Capsicum annuum L.) to determine the hormonal basis for flower bud and flower abscission as induced by low light intensity (LLI). Imposition of 80% shade for 6 days increased abscission of reproductive structures by 38% and resulted in an increase in bud ethylene production. Concomitantly, bud reducing sugars and sucrose decreased and these were negatively correlated with ethylene levels and those of its precursor, ACC. Infusion of ACC into the pedicel resulted in flower bud abscission within 48 hr. The results indicate that ethylene is the primary causal agent of pepper flower bud abscission. Production of auxin by the bud plays a role in prevention of abscission. The abscission of disbudded pedicels was prevented by infusion of NAA. Although the three cultivars had similar responses to ACC, they differed in the amount of abscission under stress, bud sugar levels, and the time of onset of ACC and ethylene production. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); α-napthaleneacetic acid (NAA); (2-chloro-ethyl)phosphonic acid (ethephon).