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Vanhoutte's spiraea has been propagated in vitro using explants from softwood growth of dormant stems forced in a solution containing 200 mg/l 8-hydroxyquinoline citrate (8-HQC) and 2% sucrose (Yang and Read, 1989). Objectives to further utilize this system were to determine the feasibility of applying plant growth regulators (PGR) via the forcing solution to softwood growth from forced dormant stems and to study the resulting influence on in vitro culture. BA and GA3 were placed in the forcing solution at various concentrations, including a zero PGR control. Explants were cultured on Linsmaier and Skoog (LS) medium containing zero PGR or different amounts of BA or thidiazuron (TDZ) or combinations of BA and IAA. Control explants placed on LS medium supplemented with 5uM BA with or without 1 or 5uM IAA, or with 0.5 or 0.75 uM TDZ alone produced the best shoot proliferation. BA in the forcing solution stimulated micropropagation, while GA3 caused less proliferation than explants from control solutions. Forcing solutions containing PGR are useful for manipulating responses of plant tissues cultured in vitro and for studying PGR influence on woody plant physiology.

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Regeneration from callus of rosemary has not been reported. Leaf segment, meristem-tip and shoot-tip explants of Rosmarinus officinalis were cultured on a Murashige and Skoog (MS) medium supplemented with five concentrations of the cytokinin thidiazuron (TDZ) alone or in combination with 3-indoleacetic acid (IAA). Callus was formed on the base and leaves of the shoottips after 6 weeks when cultured under cool white fluorescent light (26 u mol·S-1 m-2) on MS containing 0.5, 1.0, 1.5 or 2.0 mg/l TDZ. Calti were transferred to fresh MS medium supplemented with 0.2, 0.4, 0.6, 0.8 or 1.0 mg/l TDZ or 2.0, 4.0, 6.0 or 8.0 mg/l benzyladenine (BA) where shoot formation occurred. Essentiality of IAA was not clear from these experiments and further research is underway to refine regeneration protocol

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Abstract

Pretreatment of excised leaves of Petunia hybrida L. with AgNO3 permitted shoot formation equal to the control, when explants were cultured on a medium containing 6-benzylamino purine (BA), but increased callus formation, chlorophyll content, and ethylene production. When explants were cultured on a medium containing α-naphthaleneacetic acid (NAA), pretreatment with AgNO3 promoted callus growth, root formation and extension, and ethylene production, but inhibited root hair formation. Pretreatment of explants with CuSO4 suppressed ethylene production and chlorophyll content. Inclusion of AgNO3 partially overcame the effects of CuSO4 alone. When the rhizobitoxine analog, L-2-amino-4-(2-aminoethoxy)-trans-3-butenoic acid (Rh), was used for pretreatment, ethylene emanation was inhibited for 2 or 3 weeks. Number of shoots and roots, root length, root hair and callus formation were not affected by Rh except that callus growth was reduced on a medium containing NAA. NAA (1.0 mg/liter) promoted callus and root formation and induced high levels of ethylene, while kinetin (0.2 mg/liter) stimulated shoot formation but simultaneously induced much lower levels of ethylene.

Open Access

Regeneration in vitro from the embryonic axis in Phaseolus sp. has not been reported. Two embryo sizes, 0.3-0.4 mm and 0.6-0.7 mm long at 10-12 and 21 days after pollination, respectively, were excised from 4 P. vulgaris (P.v.) and 2 P. acutifolius (P.a.) genotypes. The embryonic leaves and radicale were removed, and 0.1-0.2 mm of the embryonic axis was cultured on Gamborg's B5 medium with 0, 5, 10 and 20μ MBA. The cultures were incubated in the dark at 25°C for 2 weeks followed by 1 week in continuous cool white light (25μ MS-1m2) before transferring to the second medium (0, 2μ MBA and 2μ MBA + 4μ MGA3). The tissues from the larger embryos initiated a single shoot without PGR in 30% of 1 P.v. explants and 30-60% in 2 P.a. The other 3 P.v. formed roots only. Multiple shoots were initiated in all P.v. (15-60%) and in 2 P.a. (60 and 70%) with 5 or 10μ MBA. The tissues from the smaller embryos had single shoots for all genotypes (30-60%) without PGR. Multiple shoots were initiated in 50-80% and 75-90% of the explants from P.v. and P.a., respectively, with 5 or 10μ MBA. Excess callus formed with 20μ MBA and regeneration decreased. After 3 weeks on the second medium, 6-8 shoot s/P. v. and up to 15-20 shoots/Pa. explants were observed.

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Stolon nodal segments of Buchloe dactyloides (Nutt.) Engelm. were removed from greenhouse grown plants and placed on Gamborg's B5 medium in order to determine nodal position and 2,4-D level required to give maximum callus initiation. 2,4-D levels used were 5uM, 16uM, 35uM, and 50uM. Six nodal segments were grouped according to position on the stolon, from the most recent node (node one) to the basal node (node 6). It was concluded that node 4 gave statistically greater callus mass than nodes 1, 2, 3, 5, and 6. Increasing levels of 2,4-D suppressed callus initiation, with maximum response occurring at 5uM 2,4-D.

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The leaf reaction of the Phaseolus vulgaris L. germplasm—UNECA (M6 mutant derived from the cultivar Chimbolito, Costa Rica), `Chimbolito', BAC-6 (Brazil), XAN-159 (Centro Internacional de Agricultura Tropical, Cali, Colombia), and `PC-50' (Domican Republic)—to Xanthomonas campestris pv. phaseoli strain V4S1 (Dominican Republic) were determined in two replicated trials conducted in a greenhouse in Lincoln, Neb. (Feb.–Mar. and July–Aug. 1993). `PC-50' and `Chimbolito' were susceptible to Xcp strain V4S1 in both tests. UNECA, BAC-6, and XAN-159 had similar levels of resistance to Xcp in the July to August trial. However, in the February to March trial, the resistance of UNECA was greater than that of BAC-6 but less than that of XAN-159.

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The use of buffalograss [Buchloe dactyloides (Nutt.) Engelm] in home lawns and golf courses has been increasing because of its drought resistance and low growth habit. In vitro regeneration of buffalograss at a high frequency may provide an effective tool to introduce new variation for breeding use. The positive effects of AgNO3 on friable embryogenic callus production and regeneration efficiency is well documented in maize. In order to determine if AgNO3 has the same effect on buffalograss, two vegetatively propagated cultivars, a female `609' and a male `45-3' were tested at three different concentrations of AgNO3 at 5, 10, and 15 mg·L–1 using immature inflorescences as explants. Murashige and Skoog medium supplemented with 2 mg 2,4-D/L was employed as the control medium. Medium containing AgNO3 significantly promoted the production of friable callus for `45-3' with the highest percentage achieved at 10 mg AgNO3/L. AgNO3 medium led to production of significantly larger calli than found for the control. However, no difference was detected among 5, 10, and 15 mg AgNO3/L with regard to the callus formation ability and the size of callus initiated on these three treatments. Calli were then transferred to MS medium supplemented with BA at 0.1, 0.5 or 1.0 mg·L–1 to induce shoot formation. BA at 0.5 mg·L–1 gave the best differentiation response. Calli formed in the absence of AgNO3 produced more shoots per callus, but more calli were produced in the presence of AgNO3, and the overall regeneration efficiency was much higher with AgNO3 at 10 mg·L–1. In contrast, AgNO3 showed no promotive effect on callus production and regeneration for `609'.

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Few studies on embryogenesis in common bean (Phaseolus vulgaris L.) have been reported and only the early stages of somatic embryogenesis were observed. Dry seeds from two common bean lines were germinated in darkness on L-6 medium containing 4% sucrose, 0.2 g casein hydrolysate /liter and 2.0 g phytagel /liter. The medium for seed germination was supplemented with 0, 2, 4 or 6μM forchlorfenuron (CPPU). Explants from cotyledonary leaves, petioles, hypocotyls and shoot apices were prepared from 14 day-old seedlings. Callus was derived from explant cultures incubated in darkness at 26C on the medium containing 4 μM 2,4-D and 1 μM Kinetin. The callus was transferred after 4 weeks into 125 ml Erlenmeyer flasks containing 50 ml liquid medium and placed on a gyrotary shaker (120 rpm) under cool-white light (12 μmol.m-2 .s-1 ). The liquid medium was used with 2, 4 or 6 μM of 2,4-D alone or with zeatin supplements at relative concentrations of 0.25 and 0.5. Up to 200 somatic embryos from 40 to 50 mg callus inoculations were induced after 4 to 5 weeks. Callus derived from seedlings grown on CPPU-containing medium gave more repetitive somatic embryos. Cotyledonary stage embryos with clear bipolar structure were observed only from callus derived from seedlings grown on CPPU when transferred to suspension cultures containing 2,4-D and zeatin. All somatic embryos differentiated strong roots and some developed leaf-like structures on conversion medium.

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Abstract

Ethylene (C2H4) and CO2 levels and callus formation were influenced by photoperiods (8 hours-SD; 16 hours-LD) under which ‘Nita’ dahlia stock plants were grown and leaf segments incubated in vitro. Larger callus and higher levels of C2H4 and CO2 were detected when tissues from stock plants under SD were incubated under SD (SD-SD) than when incubated under LD (SD-LD). Tissue under LD-LD or LD-SD formed similar amounts of callus to SD-LD cultures, but C2H4 and CO2 levels were higher. Compared to water-sprayed controls, 2500 mg/liter butanedioic acid mono-(2,2-dimethylhydrazide) (daminozide) sprayed on SD stock plants one day before explant removal promoted callus formation, and C2H4 and CO2 production in tissue incubated under either SD or LD. Daminozide sprayed on LD stock plants had no influence on callus or C2H4, but CO2 was increased under SD or LD incubation.

Open Access

Abstract

Shoot tip cuttings of cucumber (Cucumis sativus L.) taken at various times, ages, and condition were subjected to several pre- and post-selection techniques known to influence rooting in other species. Succinic acid-2,2-dimethylhydrazide (SADH) applied 1 week before shoot tip harvest increased the rooting of cuttings. Neither time of day cuttings were prepared (7 AM or 1 PM) nor fruit load influenced rooting. Sand culture under mist, at 27°C (day), 21° (night), in the greenhouse was superior to other rooting methods tested. Cultivars varied in rooting. Cuttings from early planting rooted better than those from late plantings.

Open Access