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Dennis P. Stimart and John C. Mather

Cotyledons from developing 6- to 8-week-old embryos of Liatris spicata (L.) Willd. (blazing star) were cultured on Murashige and Skoog medium containing 0, 0.4, 4.4, or 44.4 μm BA or 0, 0.2, 2.2, or 22.2 μm TDZ to induce adventitious shoot formation. The highest percentage of cotyledons forming the most shoots was on medium containing 2.2 μm TDZ. Cotyledon-derived callus cultured on medium containing 4.4 μm BA formed ≈16 times more adventitious shoots than on 2.2 μm TDZ. Adventitious shoots derived from cotyledons or callus produced roots when placed on MS medium containing 5.0 μm IBA. Regenerated plants that flowered in the field appeared homogeneous. Chemical names used: N6-benzyladenine (BA), thidiazuron (TDZ), indole-3-butyric acid (IBA).

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Dennis P. Stimart and Kenneth R. Schroeder

Cut flowers of a short (S)-lived (3-day) inbred, a long (L)-lived (15-day) inbred and their hybrid (F1, 7.3 days) of Antirrhinum majus L. were evaluated for fresh weight and ethylene evolution change postharvest when held in deionized water. Fresh weight change of all accessions increased 1 day postharvest then declined over the remainder of postharvest life. The loss of fresh weight was most rapid for S and less rapid for F1 and least rapid for L. Ethylene release postharvest for S and F1 started on day 1, but for L ethylene release started on day 9. Once ethylene evolution began it continued through postharvest life. On the last day of postharvest life, ethylene release from S and F1 were similar, but L was twice the level as S and F1. It appears that a slower decline in fresh weight, a delay in outset of ethylene release and higher final amount of ethylene release at senescence are heritable and associated with longer keeping time of A. majus.

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William J. Martin and Dennis P. Stimart

On-plant floret longevity and cutflower postharvest longevity (PHL) of Antirrhinum majus L., snapdragon, were evaluated using inbreds P1 (16 day PHL) and P2 (6 day PHL), F1 (P1 × P2), F2 (F1 self-pollinated), F2 × F2 (among and within PHL categories: long, 17 to 25 days; middle, 9 days; and short, 2 to 3 days), and F3 families (F2 self-pollinated). F2 on-plant floret longevity and PHL correlated to later generation PHL. Prediction of progeny PHL from F2 × F2 matings appears feasible if genotypic value for PHL of F2 is known. Selection for PHL is best based on evaluation of multiple cutflowers per genotype. Significant additive and dominant genetic variance components contribute to PHL.

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Kenneth R. Schroeder and Dennis P. Stimart

An inbred backcrossing approach was taken to transfer long postharvest keeping time of cut flowers from a white inbred line of Antirrhinum majus L. into a yellow short-lived inbred line. Three backcrosses to the short-lived recurrent parent were done followed by three generations of selfing by single-seed descent. Plants from 56 accessions of BC1S3 through BC3S3 were grown twice (June and August 1995) in a greenhouse and flower stems harvested for postharvest longevity evaluation. Postharvest evaluation was done in deionized water under continuous fluorescent light. Longevity was determined as the number of days from cutting to discard when 50% of the open florets on a flower stem wilted or turned brown. One yellow accession was retrieved that was not significantly different in postharvest longevity from the white long-lived parent. Environment substantially influenced postharvest longevity over harvest dates. Possible causes for variation of postharvest keeping time will be presented.

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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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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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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

Leaf explants of Nicotiana alata Link and Otto. were surface disinfested and cultured on Murashige and Skoog (MS) medium containing 2.66 μm N6-benzyladenine (BA) to promote shoot proliferation. After 5 weeks, proliferated shoots were removed and remaining callus saved. Callus was inoculated with Agrobacterium tumefaciens encoding a senescence-specific promoter SAG12 cloned from Arabidopsis thaliana fused to a Agrobacterium tumefaciens gene encoding isopentenyl transferase which catalyzes cytokinin synthesis. Following inoculation, the callus was cocultivated for 6 days on BA medium. Selection for transgenics was done on BA medium plus 100 mg Kanamycin and 400 mg Ticarcillin (antibiotics) per liter. Proliferating shoots were rooted on MS medium containing antibiotics. Rooted cuttings were transplanted to soil, acclimated and flowered in the greenhouse. Transgenics were outcrossed to a commercial N. alata hybrid. Seed was germinated in vitro on half-strength MS medium plus antibiotics. Segregation of transgenics to nontransgenics was 1:1. Evaluation of leaf senescence on 5-month-old plants showed 2 to 14 times fewer senesced leaves on the transgenic than the nontransgenic plants.

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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.

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Kenneth R. Schroeder and Dennis P. Stimart

Genetics of Antirrhinum majus L. (snapdragon) cut flower postharvest longevity (PHL) was investigated by generation means analysis using a white short-lived inbred (WS) and white long-lived inbred (WL) to determine mode of inheritance and heritability. Broad and narrow sense PHL heritability was estimated at 78% and 30%, respectively. Scaling tests for adequacy of an additive-dominance model in explaining PHL inheritance suggested absence of epistasis. However, joint scaling indicated digenic or higher order epistatic interactions. Fitting of a digenic epistatic model revealed significant additive effects and nonsignificant dominance and epistatic interactions. Additionally, based on sequential model fittings all six parameters [mean, additive (a), dominance (d), a×a, d×d, and a×d] proved necessary to explain observed PHL variation. Continuous variation for PHL observed in the F2 and backcross generations suggests PHL is quantitative. Assessment of associated traits revealed a positive relationship between number of flowers opening postharvest on a cut flower and PHL. In addition, floret wilting led to short PHL while floret browning was associated with long PHL.