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The influence of root initiation medium pH on root formation was investigated in relation to uptake and metabolism of applied IBA in microcuttings of Malus ×domestica Borkh. `Gala' and `Triple Red Delicious'. Root formation and uptake of H 3-IBA were related inversely to root initiation medium pH. Maximum root count (10.3 roots) and IBA uptake were observed at pH 4.0. Regardless of pH, overall root count of `Gala' was higher (13.5 roots) than `Triple Red Delicious' (4 roots). Uptake of IBA was highest at pH 4.0 for `Gala' (1.7% uptake) and at pH 4 and 5 for `Triple Red Delicious' (0.75% uptake). Metabolism of IBA was the same regardless of root initiation medium pH or cultivar examined. One-half of the IBA taken up was converted to a compound that coeluted with IBAsp during high-performance liquid chromatography. Apparently, pH regulates root formation by affecting IBA uptake but not metabolism. The level of auxin in tissue appeared unrelated to root formation between genotypes. Chemical names used: 1H-indole-3-butyric acid (IBA); 5-H 3-indole-3-butyric acid (H 3-IBA); indole-3-butrylaspartic acid (IBAsp).

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Involvement of pH and IBA on adventitious root initiation was investigated with Malus domestica Borkh. microcuttings. The pH of unbuffered root initiation medium (RIM) increased from 5.6 to 7 within 2 days. Buffering with 2[N-morpholino] ethanesulfonic acid (MES) adjusted to specific pHs with potassium hydroxide prevented pH changes and resulted in a 2-fold higher root count at pH 5.5 compared to pH 7 or unbuffered medium. As pH decreased, lower concentrations of IBA were required to increase root counts. Colorimetric measurement of IBA in buffered RIM showed greater IBA loss and higher root count were associated with lower pH levels in all cultivars. This suggests that IBA loss from RIM depends on medium pH, which affects root count. Root count differences between easy-to-root through difficult-to-root cultivars were not consistent with amount of IBA loss from RIM. Cultivar differences in root count could not be explained solely by IBA loss from RIM.

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Abstract

A single spray of 2.5 or 5% CaCl2 applied 14 days before harvest significantly reduced breakdown of ‘Spartan’ apples (Malus domestica Borkh.) in each of 4 consecutive years and caused no residual tree or crop damage. Indole-3-butyric acid (IBA) alone or in combination with CaCl2 led to significant reductions in breakdown in only 1 of the 3 seasons in which it was tested. Ca applied in 1 season did not influence fruit Ca levels the next year. Both 2.5 and 5% CaCl2 applied in 1973 significantly increased Ca in fruit peel, flesh and core tissues. Although IBA did not increase fruit Ca levels, a strong negative relationship between fruit Ca and breakdown susceptibility was evidenced by analyses in 3 crop years.

Fruits located near the top of the trees were lower in flesh Ca than those from the bottom. This, plus inadequate spray coverage in the top of the tree canopies, led to poor control of breakdown in these fruits when the sprays were applied at lx, 3x or 6x concentration with an air-blast orchard sprayer using 3342, 1114, and 557 1 of water per hectare, respectively.

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Plantlets were recovered from axillary bud cultures of muscadine grape (Vitis rotundifolia, `Summit'). Nodal segments 0.5 to 1.0 cm long were cultured in Murashige and Skoog (MS) basal medium supplemented with 5, 10, 20, or 40 μm BA. Best total shoot production was obtained with 10 μm BA; with higher BA levels, shoots were unexpanded and exhibited high mortalities. MS medium supplemented with IBA enhanced rooting by increasing rooting percentage and number per plantlet. Shoots previously proliferated on medium with 5 μm BA rooted significantly better than those multiplied on 10 μM BA. Shoot vigor during rooting was greater in shoots proliferated on 5 vs. 10 μm BA. Root development was not significantly affected by liquid vs. agar-solidifted medium or shoot length. Chemical names used: N-(phenylmethyl) -1H-purin-6-amine (BA), 1H-indole-3-butyric acid (IBA).

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Hardwood stem cuttings of eastern redcedar (Juniperus virginiana L.), taken from containerized stock plants fertilized weekly with 0, 5, 10, 20, 40, 80, 160, 320, or 640 ppm N, were treated with 7500 ppm IBA and placed under intermittent mist for 12 weeks. Foliar starch and sucrose concentrations within cuttings at time of excision were significantly correlated with percent rooting and root length, respectively. Of the mineral nutrients analyzed (N, P, K, Ca, Mg, Mn, and B), only B and K were significantly correlated with rooting response. A threshold N level (20 ppm), applied weekly, maximized rooting; higher concentrations decreased response. Although N fertilization of stock plants affected adventitious rooting, there were no significant correlations between foliar N levels and measures of rooting response. Chemical name used: 1 H- indole-3-butyric acid (IBA).

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Axillary shoots of cacao (Theobroma cacao L.), induced in vitro with cytokinins (BA or TDZ), elongated and produced leaves only in the presence of cotyledons and/or roots. Detached axillary shoots, which do not grow in `vitro under conventional tissue culture protocols, rooted with auxin and developed normally in vivo. Detached axillary shoots from cotyledonary nodes and single-node cuttings from mature plants were induced to elongate and produce normal leaves in the presence of 20,000 ppm CO2 and a photosynthetic photon flux density (PPFD) of 150 to 200 μmol·s-1·m-2. Subculture nodal cuttings continued to elongate and produce leaves under elevated CO2 and light levels, and some formed roots. Subculture of microcuttings under CO2 enrichment could be the basis for a rapid system of micropropagation for cacao. Chemical names used: N -(phenylmethyl) -1 H -purin-6-amine (BA); 1 H -indole-3-butyric `acid (IBA); α -naphthaleneacetic acid (NAA); thidiazuron (TDZ).

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Expression of the rolC gene under the constitutive CaMV 35S promoter led to several advantageous alterations in transgenic carnation (Dianthus caryophyllus L. `White Sim'). The rolC-transgenic carnation plants exhibited increased axillary budbreak and development when grown under standard commercial greenhouse conditions. Carnation with rolC generated up to 48% more stem cuttings per mother plant than nontransformed plants. Stem cuttings from rolC plants exhibited better rooting ability, with up to five times higher root dry weight than controls. The improved rooting of rolC-transgenic stem cuttings was also apparent when the cuttings were treated with IBA. During the flowering season, rolC-transgenic plants produced up to three times more flowering stems than control plants. It should be noted that the latter alterations, namely increased flowering and rooting, are of major importance to the carnation industry. Chemical name used: indole-3-butyric acid (IBA).

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Micropropagation of Pistacia vera `Mateur' was improved by adding MeJA to the multiplication and rooting media. Shoot-tip cultures established from grafted trees were maintained on a modified Murashige and Skoog medium containing 5 μm BA and 0.05 μm IBA. Adding 0.3, 1, or 3.2 μm MeJA improved shoot multiplication rates 2.5, 3.0, and 2.3, respectively. There was a significant interaction between the effects of auxin and temperature on the percentage of shoots forming roots. At 25C, the percentage of shoots forming roots was higher in the presence of NAA than IAA or IBA, whereas, at 28C, there was no difference among the auxins. Adding MeJA to the best auxin treatments-31.6 μm NAA at 25C and 31.6 μm IAA at 28C-increased the percentage of shoots forming roots and number of roots per shoot but decreased root length. More than 80% of the shoots rooted at 25C when 1 μM MeJA was added to the root induction medium, which contained 31.6 μm NAA, and the root elongation medium, without auxin. The large number of short roots induced by MeJA facilitated plantlet transfer to soil and acclimation. Chemical names used: methyl jasmonate (MeJA); N6-benzyladenine (BA), indole-3-butyric acid (IBA), α-naphthaleneacetic acid (NAA), indole3-acetic acid (IAA).

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We investigated the role of ethylene on adventitious rooting of `Gala' (easy-to-root) and `Triple Red Delicious' (difficult-to-root) apple (Malus domestica Borkh.) microcuttings. Root count increased significantly as IBA level increased, with highest root counts on `Gala'. Ethylene evolution increased significantly with IBA level without significant differences between cultivars. Basal section removal of microcuttings in the area of root origin reduced root count without changing ethylene evolution. Ethylene treatment of proliferated shoots before microcutting excision failed to enhance rooting. IBA-induced ethylene evolution was eliminated nearly by AVG, but root count remained IBA dependent. ACC reversed IBA plus AVG rooting inhibition, but ACC alone failed to influence root count. Polar auxin transport inhibitors NPA and TIBA stimulated ethylene evolution without increasing root count. Adventitious rooting of apple microcuttings was not associated with ethylene. Chemical names used: 1-H-indole-3-butyric acid (IBA); aminoethoxyvinylglycine (AVG); 1-aminocyclopropane-1-carboxylic acid (ACC); 2,3,5-triiodobenzoic acid (TIBA); N-1-naphthylphthalamic acid (NPA).

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The interactions among IBA concentrations and durations of treatment and propagation medium temperatures on the rooting of stem cuttings were compared for cultivars of Hibiscus rosa-sinensk L. Cultivar rooting was rapid with extensive root development for `Pink Versicolor', average for `Jim Hendry', and slow with few roots per cutting for `Silver Anniversary'. The IBA concentration and duration of treatment that cuttings required to reach maximum rooting declined with increase in medium temperature (from 18 to 34C). `Pink Versicolor' stem cuttings receiving 4- to 6-minute basal dips required 8000 ppm IBA with the medium at 18C, 6000 ppm at 26C, and 2500 ppm at 34C, to achieve 100% rooting of the cuttings. `Pink Versicolor' stem cuttings had the most roots at 10,000 ppm IBA, with 10-min stem dips best at 18C, 4 to 8 min at 26C, and 7 to 8 min at 34C. Maximum dry weights per root were achieved at 6000 ppm IBA, with longer basal stem dip durations needed at 18C than 26 or 34C. Lower IBA levels were required for 100% rooting of `Pink Versicolor' than for `Jim Hendry', with highest levels needed for `Silver Anniversary'. The results indicated that the benefits in rooting achieved from higher IBA levels greatly exceeded those that could be achieved by increased medium temperature. Chemical name used: indole-3-butyric acid (IBA).

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