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D.A. Dierig and R.A. Backhaus

Morphactin applied to stems of guayule (Parthenium argentatum Gray) at rates of 1000 and 5000 ppm caused significant increases in stem diameter over non-treated controls after 120 days. However, rubber content remained unchanged. Additional treatment with DCPTA did not stimulate rubber accumulation in the morphactin-treated plants. Morphactin treatments also caused a decrease in plant dry weight. Morphactin and DCPTA in combination appeared to have a negative, synergistic effect on plant growth. Lack of rubber accumulation in morphactin-treated plants was attributed to disorganized, convoluted, vascular cells within the cortical tissue, which is the primary site of rubber accumulation. Chemical names used: methyl-2-chloro-9-hydroxy-fluorene-9-carboxylate (morphactin); 2-(3,4-dichlorophenoxy)-triethylamine (DCPTA).

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Steven McArtney, Dave Ferree, John Schmid, J.D. Obermiller, and A. Green

A series of experiments were undertaken to compare the effects of individual and combined applications of GA4+7 and prohexadione-Ca (P-Ca) on scarf skin and fruit quality parameters on red strains of `Rome Beauty' and `Gala' apples. Three applications of GA4+7 at 10-day intervals beginning at petal fall (PF) significantly reduced scarf skin severity in all experiments. A single application of P-Ca at PF had no effect on scarf skin in one experiment but reduced scarf skin severity in two further experiments. Combining P-Ca with the first of three GA4+7 sprays as a tank mix reduced the severity of scarf skin more effectively than either material alone in two of three experiments at P < 0.05 and in all three experiments at P < 0.10. Combining P-Ca with the first application of GA4+7 as a tank mix generally reduced scarf skin as effectively as applying P-Ca and the first GA4+7 spray two days apart, although in one experiment, greater scarf skin control was achieved when P-Ca was applied 2 days after the first GA4+7 spray. A single application of P-Ca at PF consistently reduced, and three applications of GA4+7 consistently increased, mean fruit weight at harvest compared with the control. The economic benefits as a result of reducing scarf skin severity with P-Ca and GA4+7 sprays will need to be balanced against the negative effect of P-Ca on mean fruit weight. There is no antagonism between early season P-Ca and GA4+7 sprays for scarf skin control, and P-Ca may increase the efficacy of GA4+7 sprays for scarf skin control in apple.

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J.H. Keithly, H. Yokoyama, and H.W. Gausman

A radish (Raphanus sativus L. cv. Scarlet turnip white tipped) seedling growth test was developed to examine promotive effects of 2-(3,4-dichlorophenoxy) triethylamine (DCPTA) on seedling vigor and plant development. Compared with controls, seed treatment using 30 μm DCPTA significantly (P = 0.05) enhanced the rates of root and hypocotyl elongation and seedling dry weight. Enhanced hypocotyl development by DCPTA showed a significant linear correlation (r = 0.83) with the increased taproot yield of mature plants grown from DCPTA-treated seeds. The harvestable taproot yield and harvest index of plants grown from seeds treated with 30 μm DCPTA were increased 109% and 38%, respectively, as compared with controls. Incubation of radish seeds in 30 μm DCPTA with actinomycin-D, alpha-amanitin, amisomycin, or cordycepin significantly reduced DCTPA-mediated seedling growth. These results indicate that nuclear gene expression and translation of mRNA on 80S ribosomes are required for the acceleration of seedling development by DCPTA.

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Steven McArtney, Dick Unrath, J.D. Obermiller, and Ann Green

Experiments were conducted in commercial apple (Malus ×domestica) orchards in the southeastern U.S. between 1998 and 2006 with the primary objective of evaluating the effects of naphthaleneacetic acid (NAA) and ethephon on return bloom. NAA increased return bloom in six of 10 experiments, whereas ethephon increased return bloom in four of seven experiments. Four biweekly applications of 5 ppm NAA during June and July (early summer NAA) increased return bloom more consistently than fewer applications. Four weekly preharvest applications of 5 ppm NAA increased return bloom of ‘Delicious’ and ‘Golden Delicious’ as effectively as early summer applications. Combining NAA and ethephon in early summer sprays did not consistently increase return bloom compared with either material alone. The flower cluster density of ‘Golden Delicious’ in the year of treatment had a negative effect on return bloom that was more pronounced on control trees than trees sprayed 5 weeks after bloom with 444 ppm ethephon (48 fl oz/acre Ethrel). Combining four early summer sprays of 316 ppm ethephon (24 fl oz/acre Ethrel) with 15 ppm gibberellin A4 + A7 (GA4+7) increased return bloom of ‘Cameo’ but had no effect on return bloom of ‘Mutsu’ or ‘Golden Delicious’. Growth regulator treatments did not have a consistent effect on fruit firmness in the year of treatment. Naphthaleneacetic acid or ethephon treatments in the on year of a biennial bearing cycle can promote return bloom of apple spurs. However, the positive effect on return bloom may be minimal in cultivars with a strong natural tendency toward biennial bearing or when bloom or initial fruit set are heavy in the year of treatment.

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Duane W. Greene, Wesley R. Autio, and Paul Miller

Postbloom sprays of BA thinned `McIntosh', `Delicious', `Golden Delicious', `Mutsu, `Empire', and `Abas' apples. BA at 75 to 100 mg·liter-1 was equal to NAA at 6 to 7.5 mg·liter-1 or carbaryl at 600 to 800 mg·liter-1. BA increased fruit size, flesh firmness, and soluble solids concentration (SSC) on all cultivars evaluated. Since BA is applied during the time when cell division is occurring, it is concluded that the increased fruit size and flesh firmness were due to Increased cell numbers. Increased SSC was not due solely to increased leaf: fruit ratio. Thinning with BA was additive with other chemical thinners and no interactions were found on fruit abscission. In most eases, BA increased return bloom. Chemical names used: N-(phenylmethyl)1H-purine-6-amine [benzyladenine (BA)]; 1-naphthaleneacetic acid (NAA); 1-naphthalenyl methylcarbamate (carbaryl); butanedioic acid mono(2,2dimethylhydrazide (daminozide); (2-chloroethyl)phosphonic acid (ethephon).

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Duane W. Greene and Wesley R. Autio

Benzyladenine (BA) stimulated lateral branching on young apple (Malus domestica Borkh.) trees at concentrations as low as 100 mg·liter-1. BA reduced lateral shoot length indirectly through increased intersboot competition, whereas daminozide reduced lateral shoot growth as a direct effect of the chemical inhibition. Daminozide reduced the number of spurs that were induced by BA to grow into lateral shoots. BA reduced the size of terminal buds on spurs that were stimulated to grow into lateral shoots. When daminozide was included with BA, spur quality was increased, as determined by Increased bud size. The positive effect of daminozide on BA-treated spurs was indirect, and other growth retardants used in combination with BA may be equally effective at improving spur quality. It may not be possible to stimulate lateral branching with BA on young trees just coming into production without causing an unacceptable amount of thinning. However, on bearing `Empire' trees, lateral shoot growth was increased with BA while still achieving an appropriate level of thinning. In general, there was no advantage to applying BA in a split application. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; butanedioic acid mono(2,2-dimethylhydrazide) (daminozide).

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Tory Schmidt, Don C. Elfving, James R. McFerson, and Matthew D. Whiting

, research on biennial bearing focused on effective thinning techniques, but more recently, synthetic bioregulators have proven effective at either promoting or inhibiting floral initiation in apple. By applying a flowering promoter such as naphthaleneacetic

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Samuel Salazar-García, Luis E. Cossio-Vargas, Isidro J.L. González-Durán, and Carol J. Lovatt

development to modify the date of flowering and harvest or increase the rate of fruit development to reach legal maturity earlier are needed to broaden the harvest period and prevent the drop in fruit price. Plant bioregulators (PBRs) are known to influence

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George Ouma and Frank Matta

Experiments were conducted in 1995 and 1996 to investigate the effect of Accel and Carbaryl on apple fruit on three apple cultivars (Empire, Jon-A-Red, and Braeburn) at the Mississippi State Univ. Aricultural Experiment Station, Pontotoc. The treatments consisted of Accel 25 ppm, Accel 50 ppm, Accel 75 ppm, Carbaryl 0.05%, Carbaryl 0.2%, and an unsprayed control. Trials conducted over 2 years showed that Accel and Carbaryl consistently reduced the fruit set of three apple cultivars. There were interactions between the bioregulators and cultivars only in 1996. In all the bioregulators, treatments reduced fruit set, while in 1996, Carbaryl and Accel at all concentrations except Accel 25 ppm reduced the fruit set of `Empire', `Jon-A-Red', and `Braeburn'. Carbary 0.2% and Accel 75 ppm were the most-effective concentrations in `Empire', `Jon-A-Red', and `Braeburn', respectively, in 1996. The treatments generally increased yield and sugar content, while pH was either not affected, increased or decreased, depending on the apple cultivar.

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S.R. Drake, T.A. Eisele, M.A. Drake, D.C. Elfving, S.L. Drake, and D.B. Visser

This study was conducted over three crop seasons using 'Delicious' (Scarletspur strain) apple trees on MM.111 rootstock. The bioregulators aminoethoxyvinylglycine (AVG) and ethephon (ETH) were applied alone or in combinations at various time intervals before harvest. Fruit response to bioregulators was evaluated at harvest and after storage. AVG applied 4 weeks before first harvest retarded starch loss at harvest, retained greater firmness, and reduced internal ethylene concentration and watercore of fruit at harvest and after both regular and controlled atmosphere storage. AVG did not influence peel color (hue values), but the flesh color of treated apples was more green. AVG in all instances tended to reduce the sensory scores for apples and apple juice. In contrast, ETH enhanced starch hydrolysis, flesh color development (green to more yellow), and soluble solids concentration while reducing titratable acidity levels. ETH had no influence on fruit firmness at harvest, but reduced firmness levels after storage in an inverse relationship to the concentration applied. Sensory values for whole apples were not influenced by ETH treatment, but ETH improved sensory preference for apple juice, particularly at early harvest. Applying AVG before ETH enhanced soluble solids and sensory scores for both fruit and juice. Treating with AVG followed by ETH at 150 mg·L–1 permitted the maintenance of satisfactory firmness values (>53.4 N) after long-term storage along with better quality and sensory perceptions. Using specific combinations of both AVG and ETH permitted ETH-mediated improvements in objective and perceived fruit quality to be obtained without the losses in flesh firmness and storability due to uncontrolled ethylene evolution and ripening typically observed when ETH is applied alone preharvest.