Many physiological responses in plants are influenced by pH. The present chemiosmotic hypothesis suggests that auxin uptake into plant cells is governed by pH. Since auxin is used widely to enhance rooting, the influence of pH on 1H-indole-3-butyric acid (IBA) induced adventitious root formation was examined. Roots were initiated aseptically in 5 node apical shoot cuttings of micropropagated Malus domestica 'Gala'. Initiation was induced using a four day pulse in IBA and 15 g/L sucrose at pH 5.6 and 30C in the dark. Observations showed pH rose to 7.0 or greater within 1 to 2 days from microcutting placement in unbuffered initiation medium. Root numbers from shoots in media containing 1.5 μM IBA buffered with 10 mM 2[N-morpholino] ethanesulfonic acid (MES) to pH 5.5, 6.0, 6.5 or 7.0 with KOH resulted in average root numbers of 14.2, 10.9, 8.7, and 7.1, respectively, while unbuffered medium yielded 7,6 roots per shoot. Comparison of MES buffered medium at pH 5.5, 6.25 or 7.0 in factorial combination with IBA at 0, 0.15, 1.5, 15.0, and 150.0 μM resulted in a significant pH by IBA interaction for root number. At 0, 0.15 and 1.5 μM IBA root numbers were greatest at pH 5.5. At 15.0 μM IBA, pH 6.25 was optimal and at 150.0 μM IBA all three pH levels produced equivalent root numbers. A calorimetric assay to measure IBA removal from the initiation medium by microcuttings of `Gala' and `Triple Red Delicious' showed more IBA removal at pH 5.5 than at pH 7.0. Possible reasons for the effect of pH on adventitious root formation will be discussed.
James F. Harbage and Dennis P. Stimart
J.R. McKenna and E.G. Sutter
Experiments with field-grown hybrid Paradox (Juglans hindsii × J. Regia) walnut trees were conducted to assess the effects of stock plant water status, auxin application method, and the addition of spermine on adventitious root formation in stem cuttings. A 2-fold increase in rooting was noted when semihardwood cuttings were collected from dry (midday Ψw = –1.3 MPa) stock plants compared to the same trees six days later when fully hydrated (midday Ψw = –0.6 MPa). Spermine, when combined with potassium indolebutyric acid (KIBA) and applied as a quick dip, enhanced the rooting percentage in hardwood cuttings (54%) compared to controls treated with KIBA alone (18%). Spermine had no effect when it was applied together with KIBA using a toothpick application, producing 65% rooting compared to controls which had 75% rooting. By itself, spermine had no effect on rooting. The toothpick method for applying rooting compounds resulted in significantly higher rooting percentages for hardwood cuttings, but not for semihardwood cuttings. Combining spermine with KIBA had no effect on rooting of semihardwood cuttings.
K.G. Childs, T.A. Nell, J.E. Barrett, and D.G. Clark
Experiments were conducted to evaluate the development of stored unrooted Pelargonium × hortorum `Designer Bright Scarlet' cuttings. Treatments included storage temperature and duration and pre-storage fungicide application. Cuttings were harvested from stock plants treated with water or fungicide (Iprodione), and were stored at 60°F and 75°F for 2, 4, and 6 days. Leaf yellowing data (visual quality rating, chlorophyll fluorescence, and total chlorophyll content) were measured at the start of propagation and 7 days later. At both dates, cuttings stored but not treated with fungicide displayed more leaf yellowing after storage at 75°F for 4 and 6 days or at 60°F for 6 days compared to fungicide-treated cuttings and non-stored controls. Cutting quality was not affected by 2 days of storage, regardless of storage temperature or fungicide treatment. Fungicide-treated cuttings had less leaf yellowing after storage for 6 days at 60°F or 75°F compared to untreated cuttings, but they had more leaf yellowing than no storage controls after 7 days of propagation. Root number and root length of each cutting was measured at 14 days after start of propagation. Cuttings treated with fungicide displayed better adventitious root formation after all 4- and 6-day storage treatments compared to cuttings stored but not treated with fungicide.
Robert M. Jetton, John Frampton, and Fred P. Hain
This study tested the effects of cutting length and auxin (NAA) concentration on adventitious root formation in softwood stem cuttings from mature eastern hemlock, Tsuga canadensis (L.) Carr., and carolina hemlock, T. caroliniana Engelm. Overall rooting percentage (41%) and percent mortality (22%) were higher for eastern hemlock compared with carolina hemlock (10% rooting and 13% mortality). Rooting percentage of each species responded differently to varying auxin concentrations (0, 1, 2, 4, 8 mm NAA). Maximum rooting (56%) for eastern hemlock occurred at 0 mm NAA; then decreased with increasing auxin concentration. Carolina hemlock rooting percentage increased from the control to a maximum (16%) at 1 mm NAA; then decreased with increasing auxin concentration. For both species, the lowest mortality occurred at the same auxin concentration as maximum rooting. The highest rates of mortality coincided with the same concentrations as the lowest rooting percentages. At all auxin concentrations, eastern hemlock had a higher number of roots and greater total root length relative to carolina hemlock. Mortality among 6-cm stem cuttings was twice that observed for 3-cm cuttings of both species. However, 6-cm cuttings of eastern hemlock that did form adventitious roots had more roots and longer total root length compared with 3-cm cuttings. Chemical name used: 1-naphthalenacetic acid.
Joseph J. King and Dennis P. Stimart
In an attempt to analyze genetically the interaction of endogenous auxin concentration and adventitious root formation, an EMS mutagenized M2 population of Arabidopsis thaliana was screened for mutants with altered abilities to form adventitious roots. A selected recessive nuclear mutant, rooty (rty), is characterized by extreme proliferation of roots, inhibition of shoot development and other morphological alterations suggestive of auxin or ethylene effects. The rty phenotype occurs in wild type seedlings grown on auxin containing medium and relatively normal growth is stimulated in rty seedlings growing on cytokinin containing medium. Analysis by GC-MS found that endogenous IAA concentrations in rty are 2 to 17 times higher than in wild type depending on tissue type and IAA form. Dose response experiments with IAA and NAA indicated that rty does not express increased sensitivity to auxin. These data suggest that the rty phenotype is due to elevated endogenous auxin. A genetic map location for rty and possible roles for the wild type RTY gene product in regulating auxin concentration will be presented.
Mohammed M. Al-Salem and Nabila S. Karam
Stem cuttings of Arbutus andrachne L. were taken from basal or terminal portions of branches in October and treated with acid or salt forms of IBA or NAA at several concentrations. Also, the effects of wounding and propagation medium were assessed. Auxin was necessary for root formation, IBA acid being most effective. In general, salt forms of IBA and NAA were less effective than acid forms. Concentration of auxin had a significant effect on rooting regardless of auxin type or chemical form. The greatest rooting percentage, root number, length, and fresh and dry weights were exhibited by basal cuttings treated with 24 mm IBA. Position of the cutting on the branch did not affect rooting except when the IBA acid form was used; basal cuttings were then superior to terminal ones. Wounding, by making two opposite longitudinal incisions at the base of the cutting, increased rooting. The propagation medium had a significant effect on adventitious root formation, which was enhanced with increasing perlite percentage in the medium up to 100%. Chemical names used:1H-indole-3-butyric acid (IBA); α-naphthaleneacetic acid (NAA).
Christopher L. Rosier, John Frampton, Barry Goldfarb, Frank A. Blazich, and Farrell C. Wise
Seven concentrations of IBA and seven concentrations of NAA plus a nonauxin control were tested over three growth stages to determine their effectiveness in promoting adventitious root formation on stem cuttings taken from 3- and 4-year-old stock plants of Fraser fir [Abies fraseri (Pursh) Poir.]. Cuttings were prepared in March (hardwood), June (softwood), or November (semi-hardwood) 2001, treated with auxin concentrations ranging from 0 to 64 mm, and placed under mist. Rooting percentage, percent mortality, number of primary roots, total root length, root system symmetry, and root angle were recorded after 16 weeks. Growth stage and auxin concentration significantly affected every rooting trait except root angle. NAA significantly increased the number of primary roots and total root length. However, auxin type did not significantly affect rooting percentage or percent mortality. The highest rooting percentages (99%) occurred when softwood cuttings were treated with 5 mm auxin, however, semi-hardwood cuttings also rooted at high percentages (90%) and had no mortality when treated with 14 mm auxin. Regardless of auxin type, the number of primary roots and total root length varied in similar patterns across concentration, although, NAA tended to induce a greater response. To root Fraser fir stem cuttings collected from 3- and 4-year-old stock plants, it is recommended that a concentration of 5 mm NAA should be used on softwood cuttings and 14 mm IBA on semi-hardwood cuttings. Chemical names used: indole-3-butyric acid (IBA); 1-naphthaleneacetic acid (NAA).
Wen-Quan Sun and Nina L. Bassuk
Single-node `Royalty' rose (Rosa hybrida L.) cuttings were used to examine the relationship between adventitious root formation, budbreak, and ethylene synthesis following IBA treatment. IBA was applied as a lo-second basal quick dip before rooting, and AIB, GA3, STS, and ethephon were applied either as basal dips or foliar sprays. IBA application increased rooting and inhibited budbreak of cuttings. IBA 2 600 mg·liter-1 greatly inhibited budbreak during 4 weeks of rooting. IBA treatment stimulated ethylene synthesis, which was inversely correlated with budbreak of cuttings. Ethephon also significantly inhibited budbreak. Budbreak of rose cuttings was completely prevented by repeated ethephon sprays used to maintain high endogenous ethylene levels during the first 10 days. Treatment with STS, an ethylene-action inhibitor, improved budbreak. The inhibition of budbreak by IBA treatment resulted primarily from elevated ethylene levels. Root initiation and root elongation of cuttings initially inhibited budbreak, but later promoted budbreak. Chemical names used: indole-3-butyric acid (IBA); gibberellic acid (GA3); silver thiosulfate (STS); AIB, aminoisobutyric acid (AIB); (2-chloroethyl)-phosphoric acid (ethephon).
Anthony V. LeBude*, Barry Goldfarb, and Frank A. Blazich
Producing high quality rooted stem cuttings on a large scale requires precise management of the rooting environment. This study was conducted to investigate the effect of the rooting environment on adventitious root formation of stem cuttings of loblolly pine (Pinus taeda L.). Hardwood stem cuttings of loblolly pine were collected in Feb. 2002 from hedged stock plants and stored at 4 °C until setting in Apr. 2002. One hundred stem cuttings per plot in each of two replications received 45, 61, 73, 102, 147, or 310 mL·m-2 of mist delivered intermittently by a traveling gantry (boom) system. Mist frequency was similar for all treatments and was related inversely to relative humidity (RH) within the polyethylene covered greenhouse. Rooting tubs in each plot were filled with a substrate of fine silica sand, and substrate water potential was held constant using soil tensiometers that activated a subirrigation system. Cutting water potential was measured destructively on two cuttings per plot beginning at 0500 hr every 3 hh until 2300 hr (seven measurements) 7, 14, 21, or 28 days after setting. During rooting, leaf temperature and RH were recorded in each plot to calculate vapor pressure deficit (VPD). Cutting water potential and VPD were strongly related to mist application. Cutting water potential was also related to VPD. Rooting percentage had a linear and quadratic relationship with mean cutting water potential and VPD averaged between 1000 and 1800 HR. Eighty percent rooting occurred within a range of values for VPD. Data suggest that VPD can be used to manage the water deficit of stem cuttings of loblolly pine to increase rooting percentage. These results may be applicable to other species and to other rooting environments.
Mohamed S. Elmongy, Xiuyun Wang, Hong Zhou, and Yiping Xia
, sugars have a signaling function and are considered regulatory molecules during plant development ( Chu et al., 2010 ). Adventitious root formation includes many complex stages that are regulated by a number of external or internal factors ( Trevisan et