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Dennis P. Stimart

The Allen Centennial Gardens are instructional gardens managed by the Department of Horticulture, University of Wisconsin-Madison. Twenty-two garden styles exist on the 2.5-acre (1.0-ha) campus site with a primary focus on herbaceous annual, biennial and perennial ornamental plants. The gardens are used for instruction mostly by the Department of Horticulture and secondly by departments of art, botany, entomology, landscape architecture, plant pathology, and soils. Class work sessions are limited due to the gardens' prominence on campus, high aesthetic standards, space restrictions, and large class sizes. Undergraduate students are the primary source of labor for plant propagation, installation and maintenance; management; and preparation of interpretive literature. Work experience at the gardens assists students with obtaining career advances in ornamental horticulture. Future challenges include initiating greater faculty use of the gardens for instruction and creating innovative ways to use the gardens to enhance instruction.

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Rozlaily Zainol and Dennis P. Stimart

Genetic analysis of a white double-flowering Nicotiana alata is being investigated. Self-pollination of the double-flowering plant produced all double progeny. Reciprocal hybridization of the double-flowered selection with N. alata cultivars produced nondouble F1 progeny that segregated 3:1 (nondouble to double) in the F2 generation. Reciprocal backcrosses of F1 plants to the parents resulted in nondouble progeny when backcrossed to the nondouble parent and 1:1 segregation when backcrossed to the double parent. Intercross of F1 plants resulted in progeny segregating 3:1. Double flowering habit has been transferred to white, red, salmon, green, and bicolor N. alata. Results suggest double flowering is under nuclear control regulated by a recessive allele.

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Rozlaily Zainol and Dennis P. Stimart

A double-flower form of Nicotiana alata Link & Otto was characterized genetically as a monogenic recessive trait expressed when homozygous. Reciprocal crosses demonstrated no maternal effect on expression of double flowers. A single dominant gene expressed in the homozygous or heterozygous state caused the single-flower phenotype. The symbol fw is proposed to describe the gene controlling double-flower phenotype.

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James F. Harbage and Dennis P. Stimart

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.

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Kenneth R. Schroeder and Dennis P. Stimart

In an effort to reduce chemical usage to prolong postharvest keeping time of cut flowers, a cross was made between a long-lived (vase life, 10.9 days) inbred line of Antirrhinum majus and a short-lived (vase life, 5.0 days) inbred line. The F1 hybrid was backcrossed to the short-lived parent. Sixty plants of the BC1 generation were carried on through three generations of selfing by single-seed descent. Eight replications each of 60 BC1S3 families, the parents, and the F1 hybrid were grown in the greenhouse, harvested with 40-cm stems when five florets opened, and placed in distilled water for vase life evaluation. Stems were discarded when 50% of the florets on a spike wilted, browned, or dried. Three families proved not significantly different from the long-lived inbred parent. Results indicate that inbred backcross breeding shows potential to increase the postharvest keeping time of short-lived Antirrhinum majus inbred lines.

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Dennis P. Stimart and James F. Harbage

The role of the number of adventitious roots of Malus domestics Borkh. `Gala' microcuttings in vitro on ex vitro root and shoot growth was investigated. Root initiation treatments consisted of IBA at 0, 0.15, 1.5, 15, and 150 μm in factorial combination with media at pH 5.5, 6.3, and 7.0. IBA concentrations significantly influenced final root count and shoot fresh and dry weights, but not plant height, leaf count, or root fresh and dry weights at 116 days. Between 0 and 0.15 μm IBA, final root counts were similar, but at 1.5, 15, and 150 μm IBA, root counts increased by 45%, 141%, and 159%, respectively, over the control. The pH levels did not affect observed characteristics significantly. There was no significant interaction between main effects. A significant positive linear relationship was found between initial and final root count. The results suggest a limited association between high initial adventitious root count and subsequent growth. Chemical name used: 1 H -indole-3-butyric acid (IBA).

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Susan M. Stieve and Dennis P. Stimart

Selecting for increased postharvest longevity through use of natural variation is being investigated in Antirrhinum majus (snapdragon) in order to decrease postharvest chemical treatments for cut flowers. The postharvest longevity of eighteen white commercial inbreds was evaluated. Twelve stems of each inbred were cut to 40 cm and placed in distilled water. Stems were discarded when 50% of spike florets wilted or browned. Postharvest longevity ranged from 3.0 (Inbred 1) to 16.3 (Inbred 18) days. Crossing Inbred 18 × Inbred 1 yields commercially used Hybrid 1 (6.6 days postharvest). The F2 population averaged 9.1 days postharvest (range 1 to 21 days). F3 plants indicate short life postharvest may be conferred by a recessive gene in this germplasm. Populations for generation means analysis as well as hybrids between short, medium and long-lived inbreds were generated and evaluated for postharvest longevity.

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Kenneth R. Schroeder and Dennis P. Stimart

Gibberellic acid (GA3) and photoperiod were used in combination in an effort to reduce generation time of Antirrhinum majus L. Four commercial inbred lines of A. majus were started from seed and grown in a glasshouse in winter 1993-94. GA3 was applied as a foliar spray every 2 weeks at 0, 144, 289, 577, or 1155 μm starting 5 weeks after seeds were sown. Supplemental lighting (60 μmol·m–2·s–1) from 0600 to 2000 hr and night interruption from 2300 to 0300 hr was used throughout the experiment. Data were collected weekly on plant height and leaf count from the start of GA3 treatments through anthesis. Time to flowering was determined as days from seed sowing to anthesis. GA3 treatment of A. majus under a long-day photoperiod increased time to flowering, plant height and leaf count. It would appear that long-days may have overridden the floral induction effects of GA3.

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Kenneth R. Schroeder and Dennis P. Stimart

Three percent hydrogen peroxide (H2O2) was diluted with deionized water (dH2O) to 0.75%, 0.38%, 0.19%, 0.09%, or 0.05% H2O2 plus 1.5% sucrose for use in evaluation of Antirrhinum majus L. (snapdragon) cut flowers. Other vase solutions used as controls included; 300 ppm 8-hydroxyquinoline citrate (8-HQC) plus 1.5% sucrose; dH2O plus 1.5% sucrose; and dH2O. A completely random design with 7 replicationss was used. Flowering stems of three commercial inbreds and one F1 hybrid of snapdragon were cut when the first five basal florets opened. Each stem was placed in an individual glass bottle containing one of the eight different treatments. Flowering stems were discarded when 50% of the open florets wilted, turned brown, or dried. Postharvest life was determined as the number of days from stem cutting to discard. Addition of H2O2 to vase solutions at rates of 0.19 and 0.09% resulted in postharvest life not different from that obtained with 8-HQC plus sucrose. Hydrogen peroxide plus sucrose extended postharvest life of snapdragon cut flowers 6 to 8 days over dH2O and 5 to 7 days over dH2O plus 1.5% sucrose.

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Kenneth R. Schroeder and Dennis P. Stimart

One-centimeter hypocotyl explants from 2-week-old Antirrhinum majus L. (snapdragon) seedlings germinated and grown in vitro under 12-h cool-white fluorescent light and 12 h dark or 24 h dark were placed on Murashige and Skoog (MS) medium containing 0, 0.44, 2.22, 4.44, 8.88, or 44.4 μM N6-benzyladenine (BA). Cultures were maintained under the light/dark regime at 25°C. After 2 weeks, adventitious shoots were counted. A shoot was considered adventitious and counted if a stem and leaf developed. Shoots developed along the entire length of the hypocotyl sections. Mean shoot production per hypocotyl explant ranged from 2.4 to 6.1 shoots when seedlings were germinated and grown in 24 h darkness and 2.2 to 10.9 shoots when started in the light/dark regime. Highest shoot counts were attained /from hypocotyl explants when seedlings were germinated and grown under the light/dark regime for 2 weeks and transferred to 2.22, 4.44, or 8.88 μM BA. Shoot development appeared normal at the 2.22 and 4.44 μM level, while at 8.88 μM BA, development was slightly abnormal along with slightly more callus production.