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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

Abstract

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).

Open access

Bruce W. Wood

Abstract

In an attempt to solve the problems of nonuniform and delayed shuck dehiscense of pecan [Carya illinoensis (Wangenh.) C. Koch], ethephon and NAA were evaluated for their efficacy as harvest-aid treatments. A 3-year study under commercial-like orchard conditions using 75-year-old ‘Stuart’ trees resulted in a spray mixture of 9 mm ethephon and 1.5 or 3.0 mm NAA, or just 9 mm ethephon alone, accelerating shuck dehiscence by 1 to 2 weeks relative to that of the nontreated control. While all three treatments induced some degree of leaflet abscission, the two treatments employing the NAA and ethephon combination induced only about one-fourth (21% vs. 75%) as much leaflet abscission as when ethephon was used alone. However, this level of leaflet abscission (21%), plus an associated 50% drop in net photosynthesis for several days post-treatment, was sufficient to reduce in-shell nut yields in subsequent years. This appears to preclude commercial acceptability of such treatments for pecan. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon), 1-napthaleneacetic acid (NAA).

Open access

Duane W. Greene and Wesley R. Autio

Abstract

Five chemical thinning trials, conducted over 4 years, indicated that BA is an effective thinner for ‘McIntosh’ apples (Malus domestica Borkh.). Although it can thin at concentrations as low as 25 mg·liter−1, in most years a higher concentration was required to thin adequately. It appeared that 14 to 18 days after full bloom, when fruit size was about 10 mm, may be the period when maximum thinning was achieved. Greater thinning occurred when BA and carbaryl were combined than when they were used individually. BA increased fruit weight, flesh firmness, and soluble solids content at harvest relative to no thinning. The storage life of fruit treated with BA was less than that of fruit from nonthinned trees, but this effect may have been an indirect response related to the larger fruit size rather than a direct response to the chemical. BA caused thinning and induced lateral branching simultaneously on young ‘Macspur McIntosh’ trees. Therefore, crop load on trees just coming into production may be significantly reduced when BA is used to induce lateral branching. Chemical names used: N-(phenylmethyl)-IH-purine-6-amine [benzyladenine (BA)], 1-napthaleneacetic acid [NAA], 1-naphthalenyl methylcarbamate [carbaryl].