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Dennis P. Stimart and Kenneth R. Schroeder

Cut flowers of a short(S) lived (3 days) inbred, a long(L) lived (15 days) inbred and their hybrid (F1, 7.3 days) of Antirrhinum majus L. were evaluated for water loss when held in deionized water under continuous fluorescent light at 25°C. Flowering stems for water loss evaluation were harvested when the basal five to six florets expanded. Cut stems were placed in narrowed-necked bottles with the open area between the stem and bottle sealed with Parafilm. Stem weight and water weight in the bottle were taken every 24 h. Water loss evaluation was continued until 50% of the open florets on the flowering stem wilted or turned brown. Overall, water loss from all accessions was highest 24 h postharvest, declined rapidly between 24 to 96 h, and remained unchanged throughout the remainder of postharvest life. Between 24 to 96 h, the slope of the line for water loss was greatest for L, least for S, and intermediate for the F1. It appears that longest postharvest life of A. majus is associated with the most rapid decline of water loss immediately postharvest to a level, which remains constant.

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Kenneth R. Schroeder and Dennis P. Stimart

Flowering stems from three commercial inbreds and their F1 hybrids of Antirrhinum majus L. were cut when the first eight basal florets opened. Tops of the stems were removed above the eighth floret and florets were removed leaving two, four, six, or eight open florets on a stem. A completely random design with 10 replications was used. Flowering stems were placed in plastic storage containers 35 × 23 × 14 cm (L × W × H) with 2.5 L deionized water for postharvest evaluation. Evaluation took place under continuous cool-white fluorescent light (9 μmol·m–2·s–1) at 24°C Postharvest life was determined as the number of days from cutting to discard when 50% of the open florets on a flowering stem wilted, turned brown, or dried. Results showed postharvest life increased as the number of open florets on a stem decreased. Mean postharvest life increased as much as 4.7 days when only two florets remained on a stem. These results indicate a direct relationship between number of florets on a cut flower stem and postharvest life.

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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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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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William J. Martin and Dennis P. Stimart

Cut flowers of Antirrhinum majus L. (snapdragon) P1, P2, F1, F3, and F2 × F2 plants were harvested after the first five flowers were open and were evaluated for postharvest longevity to further evaluate genes conditioning postharvest longevity. F3 progeny evaluated were derived by selfing F2 selections of long keeping, mid-range, and short keeping types. F2 × F2 progeny evaluated were derived from crosses within and between postharvest longevity categories. Populations for evaluation were grown in the greenhouse in winter 1998-1999 in a randomized complete-block design according to standard forcing procedures. Thirty plants of each genotype were held in the laboratory in deionized water under continuous fluorescent lighting at 22 °C for postharvest assessment. The end of postharvest life was defined as 50% of the flowers drying, browning, or wilting. Data will be presented on postharvest longevity and allelic relationships within populations.

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Monica E. Figueroa-Cabanas and Dennis P. Stimart

Direct shoot organogenesis (DSO) on Antirrhinum majus L. (snapdragon) was evaluated in vitro to determine the inheritance of genes conditioning this response. One-centimeter-long hypocotyls excised from 2-week-old seedlings started in vitro in the dark on Murashige and Skoog medium served as explants. Optimal conditions for DSO on explants included hypocotyl excision from 10-day-old seedlings, 2.22 μmol BA in the culture medium, and a 21-day culture duration. An adventitious shoot was counted once it developed a stem terminated by at least one leaf appearing to have originated from an apical meristem. Seven populations were evaluated for DSO: parent 1 (P1) with lowest DSO (0.3 shoots); parent 2 (P2) with highest DSO (13.9 shoots); F1 (P1 × P2); F1 (P2 × P1); F2 (self-pollination of F1); P1 × [P1 × P2]; and P2 × [P1 × P2]. P1 and P2 were chosen as parents based on DSO counts being lowest and highest, respectively, of inbreds evaluated. DSO appears to be a trait under nuclear genetic control. High DSO appears to be dominant over low DSO. The trait appears to be simply inherited through one or two genes.

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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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Susan M. Stieve and Dennis P. Stimart

Eighteen commercially used white Antirrhinum majus (snapdragon) inbreds, a hybrid of Inbred 1 × Inbred 18 (Hybrid 1) and an F2 population (F2) of Hybrid 1 were evaluated for stomatal size and density and transpiration rate to determine their affect on postharvest longevity. Stems of each genotype were cut to 40 cm, placed in distilled water and discarded when 50% of florets wilted or browned. Postharvest longevity of inbreds ranged from 3.7 to 12.9 days; Hybrid 1 and the F2 averaged 3.0 and 9.1 days postharvest, respectively. Leaf impressions showed less than 3% of stomata were found on the adaxial leaf surface. Inbred abaxial stomatal densities ranged from 128.2 to 300.7 stomata mm-2; Hybrid 1 and the F2 averaged 155 and 197 stomata mm-2, respectively. Transpiration measurments on leaves of stems 24 hr after cutting were made with a LI-COR 1600 Steady State Porometer. Statistical analysis showed inbreds were significantly different based on postharvest longevity, stomatal size and density and transpiration of cut stems.

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Dennis P. Stimart and John C. Mather

Cotyledons from developing embryos 6 to 8 weeks old of Liatris spicata (blazing star) were cultured on Murashige-Skoog (MS) medium containing 0, 0.4, 4.4, and 44.4 μ M benzyladenine (BA) or 0, 0.2, 2.2, and 22.2 μ M thidiazuron (TDZ) to induce adventitious shoot formation. The highest percent of cotyledons forming shoots with highest shoot counts was on medium containing 2.2 μ M TDZ. Vitreous shoots formed on medium with 22.2 μ M TDZ. Callus derived from cotyledons and cultured on medium containing 4.44 μ M BA or 2.2 μ M TDZ formed adventitious shoots with highest shoot counts on 4.44 μ M BA. Adventitious shoots derived from cotyledons and callus were rooted on MS medium with 5.0 μ Mindole-3-butyric acid, acclimatized and grown ex vitro. All micropropagated plants appeared similar to each other.

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Kenneth R. Schroeder and Dennis P. Stimart

Leaf impressions were made from two short-lived (4 and 5 d) inbreds, a long-lived (11 d) inbred, and their hybrids (8 and 9 d) of Antirrhinum majus L. using Super Glue and glass microscope slides. Leaves were taken from mid stem, pressed on glass slides (under side down), spread with a small amount of Super Glue, set for 3 to 4 s. Then, the leaf was peeled off leaving a permanent impression in the glue. Slides were placed under a microscope equipped with a video imaging system and computer images were taken to facilitate counting of stomatal complexes. Number of stomata ranged from 10,400 to 21,300 per cm2 of leaf. A LI-COR LI-3100 area meter (LI-COR, Inc. Lincoln, Neb.) was used to measure total leaf area of 40-cm cut flower stems of each accession. Stomata per flowering stem ranged from 1,074,000 to 2,282,000, with the long-lived inbred having the fewest stomata, the hybrids intermediate with 11% to 21% more, and the short-lived inbreds having 40% to 113% more stomata per stem. It appears long postharvest life of A. majus is associated with flowering stems with fewer stomata per cut stem.