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)].
Paul T. Wismer, J.T.A. Proctor, and D.C. Elfving
Lisa M. Perkins and Gary J. Kling
Root systems of two Magnolia taxa were treated with spray applications of auxins to determine their effects on root regeneration. Spray application of 500 ppm of IBA doubled the number of adventitious roots regenerated from the cut ends of main roots in 1-year-old cuttings of Magnolia × Soulangiana (Soul.-Bod). Higher concentrations of IBA inhibited root regeneration. Auxin applications did not increase the number of lateral or branch roots. Root systems of Magnolia × Soulangiana were treated with spray applications of ethanol to determine effect of IBA on root regeneration. A significant negative linear relationship was found between ethanol concentration and the number of adventitious roots initiated at the cut ends of main roots. Ethanol concentrations of 12.5% to 70% had no effect on the number of lateral roots. Root regeneration of Magnolia × ‘Betty’ was not stimulated with soil drench applications of 250 to 1000 ppm IBA. IBA and NAA concentrations of 1000 to 4000 ppm were inhibitory. Chemical names used: 1H-indole-3-butyric acid (IBA), 1-napthaleneacetic acid (NAA).
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).
Bruce W. Wood
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).
Duane W. Greene and Wesley R. Autio
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].
Richard M. Manshardt and Timothy F. Wenslaff
A study of reproductive barriers limiting interspecific hybridization between Carica papaya L. and C. cauliflora Jacq. was undertaken in four reciprocal interspecific crosses using two different lines of each species. Particular attention was focused on determining whether polyembryonic clusters produced in these crosses were of maternal or zygotic origin. Prezygotic barriers were unimportant; pollen tube penetration and zygote formation were similar in intra- and interspecific crosses. Substantial postzygotic disruptions were observed, including disorganized growth and abortion of hybrid embryos and lack of normal endosperm development. In most crosses, disorganized embryos aborted before differentiating into polyembryonic structures. However, crosses employing UH345 (C. cauliflora) as female parent produced some embryos that developed to maturity (6 months), and, in these crosses, embryogenic proliferation from zygotic tissue became evident as early as the beginning of the 3rd month. There was no evidence of somatic embryogenesis from maternal tissues in any cross. Embryos rescued 3 to 6 months after pollination continued embryogenic growth in vitro on basal Murashige and Skoog (MS) medium and germinated on medium containing 0.2 mg BA/liter and 0.5 mg NAA/liter. Zymograms assayed for isocitrate dehydrogenase, malate dehydrogenase, and phosphoglucomutase activity confirmed the zygotic origin of tissues taken from in vitro cultures and recovered plantlets. Vigor, viability, and fertility (< 1% stainable pollen) of hybrids recovered from embryo culture were low. Chemical names used: 6-benzylaminopurine (BA); 1-napthaleneacetic acid (NAA).
Robert L. Geneve, Wesley P. Hackett, and Bert T. Swanson
An in vitro system has been developed to study adventitious root initiation in the juvenile and mature phases of English ivy (Hedera helix L.). The system uses de-bladed petiole explants cultured in a defined liquid medium. Adventitious roots are visible macroscopically after 18 days. Juvenile petiole explants show a dose-response to auxin application with optimal root initiation at 100 μM NAA or IAA. With optimal auxin concentration, root initials form in juvenile petiole explants directly from cortical parenchyma cells, which involves induction (1–6 days), meristem organization (6–9 days), and root elongation stages (9–18 days). Sucrose is required for outgrowth of root primordia but not for initiation of primordia. Mature petiole explants respond to auxin with random cell divisions in cortical parenchyma cells; root initials form at a low frequency from callus resulting from this cortical cell division. Distribution of 14C at various times after administration of 14C-labeled NAA is similar in juvenile and mature petioles. Because of their difference in rooting potential, coupled with similarity in anatomical organization, distribution of 14C from NAA, and identical genotype, juvenile and mature petioles provide an excellent experimental system for analyzing the morphogenetic, physiological, and genetic basis of rooting potential. Chemical names used: 1-napthaleneacetic acid (NAA); 1H-indoIe-3-acetic acid (IAA).
Christopher B. Cerveny, James L. Gibson, and James E. Barrett
Orange Jasmine (Murraya paniculata L. Jack) and Texas Star [Tecoma stans (L.) Juss.] are two tropical ornamentals which have become popular in the specialty floriculture crop market because of their outstanding flower characteristics. Unfortunately they are difficult to root and little has been published on how to propagate them effectively. Therefore, the objective of our experiment was to determine the optimum physiological age of stem tissue necessary to effectively root 2-node stem cuttings. Forty-five cm shoots of Murraya were harvested on 27 June and 7 Sept. 2005, and divided into 2-node stem cuttings representing the top, middle, and bottom sections of the stem (soft-wood, semi-hardwood, and hardwood, respectively). Cuttings were measured for stem length and diameter, dipped in a 1,500 mg·L–1 solution containing indolebutyric acid (IBA) 1%: napthaleneacetic acid (NAA) 0.5%, and propagated under mist for 10 weeks in a 4 perlite: 1 vermiculite substrate (by volume). Tecoma followed a similar regime but were harvested once on 13 Sept. and evaluated 4 weeks after planting. Both species were evaluated for percent survival and rooting quality on a 1 to 5 scale; 1 = poor, 5 = best. Stem quality differences in Tecoma cuttings were shown, but did not influence rooting performance or percent survival. Murrayacuttings indicated a similar trend suggesting that age of tissue is not an important factor when propagating these species. However, when comparing the two harvest dates, data from Murraya cuttings showed an increase in survival from 79% and 95% and an increase in rooting quality from 2.72 to 4.26 when harvested in June compared to Sept., respectively. Cuttings harvested in Sept. were also shown to be 17% shorter with a 126% larger diameter than those harvested in June. These data suggest a trend toward a seasonal effect when harvesting cuttings of Murraya paniculatain Florida. Further studies should be conducted to verify this trend and to identify the ideal season for propagation.
Christopher B. Cerveny and James L. Gibson
Bougainvillea glabra is a tropical species with reportedly difficulty to propagate. Previous research has shown the importance of talc-based rooting hormones when propagating Bougainvillea, yet little has been published on the efficacy of liquid-based formulations. Therefore, our objective was to determine the optimum concentration of indolebutyric acid potassium salt (KIBA) needed to effectively root semi-hardwood stem cuttings of Bougainvillea `California Gold' and `Helen Johnson'. Sub-terminal cuttings measuring 6.5 cm were harvested from stock plants of Bougainvillea on 3-week intervals from 6 June to 8 Aug. and repeated 6 Sept. to 8 Nov. 2005. Cuttings were dipped 0.5 cm in a solution of 0, 1500, 3000, or 6000 mg·L-1 KIBA or in a 1500-mg·L-1 solution containing indolebutyric acid (IBA) 1%: napthaleneacetic acid (NAA) 0.5% and propagated under mist. Cuttings were evaluated for percent survival, rooting quality (1 = poor; 5 = best), and number of primary and lateral roots 5 weeks after planting (WAP). Differences in `California Gold' for percent survival, average rank, and number of roots were determined not significant at P ≤ 0.05. However, application of rooting hormone to `Helen Johnson' increased rooting quality, number of primary roots, and number of lateral roots by up to 24%, 53%, and 50%, respectively. Results indicated rooting performance was generally improved with application of KIBA; therefore, cuttings of Bougainvillea may benefit from a 1500-mg·L-1 solution. KIBA was also found to be as effective as the industry standard liquid formulation. Growers will have to consider the availability and cost of KIBA when propagating Bougainvillea.
Carol Gonsalves, Baodi Xue, and Dennis Gonsalves
Six summer squash (Cucurbita pepo L.) cultivars were regenerated via somatic embryogenesis using cotyledons excised from germinated or nongerminated seeds. Genotypes included were zucchini, commercial F1 hybrids, `President', `Seneca Zucchini', `Jade'; the noncommercial inbred line `Caserta Inbred 557311'; and two yellow squash hybrids `Dixie' and `Seneca Butterbar'. Somatic embryogenesis was initiated in induction medium containing 22.62 μm 2, 4-D, and embryos were germinated in maturation medium containing 0.27 μm NAA and 0.23 μm kinetin. Plants were elongated and rooted on basal medium without hormones. All media contained carbenicillin at 500 mg·liter–1. Sixty-one percent of the `Seneca Butterbar' cotyledons produced somatic embryos when kept on induction medium for 10 weeks. Overall, 7% of the initial explants produced plantlets, and regeneration efficiency was calculated as 0.3 plantlets per initial explant. The relative production of plants from cotyledons that were kept on induction medium for different time periods were determined for `Caserta Inbred 557311' and `Seneca Zucchini'. All cotyledons produced somatic embryos after 11 to 17 weeks on induction medium. However, plantlet production was optimal with explants kept on induction medium for 13 weeks for `Seneca Zucchini' and for 15 weeks for `Caserta Inbred 557311', producing an average of 4.5 and 9.3 plants per explant, respectively, from 90% to 70% of the explants. We recovered plants from all six cultivars; thus, our regeneration protocol may be applicable to other genotypes. The high percentage of regenerants obtained indicates that the regeneration method is efficient enough to be adapted successfully to squash transformation experiments. Chemical names used: α-carboxybenzylpenicillin (carbenicillin); 2,4-dichlorophenoxyacetic acid (2,4-D); 6-furfurylaminopurine (kinetin); α-napthaleneacetic acid (NAA).