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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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William J. Martin and Dennis P. Stimart

Stomatal density during plant development and inheritance of the trait were investigated with the goal of utilizing stomatal density as a correlated trait to cutflower postharvest longevity in Antirrhinum majus L. Inbred P1 (stomatal index = 0.2) was hybridized to inbred P2 (stomatal index = 0.3) to produce F1 (P1 × P2), which was backcrossed to each parent producing BCP1 (F1 × P1) and BCP2 (F1 × P2). P1, P2, F1, BCP1, and BCP2 were used to examine changes in stomatal density with plant development and early generation inheritance. An F2 (F1 self-pollinated), and F3, F4, and F5 families, derived by self-pollination and single seed descent, were used to obtain information on advanced generation inheritance. Stomatal density was stable over time and with development of leaves at individual nodes after seedlings reached two weeks of age. Therefore, stomatal density can be evaluated after two weeks of plant development from a leaf at any node. Stomatal density is quantitatively inherited with narrow sense heritabilities of h2 F2:F3 = 0.47 to 0.49, h2 F3:F4 = 0.37 ± 0.06 to 0.60 ± 0.07, and h2 F4:F5 = 0.47 ± 0.07 to 0.50 ± 0.07.

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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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William J. Martin and Dennis P. Stimart

Stomatal density is being investigated as a highly correlated trait to postharvest longevity (PHL) and subsequently may be used for selection in early generations of breeding germplasm. To this end, leaf imprints were created from Antirrhinum majus L. (snapdragon) P1, P2, F1, BC1 (F1×P1), BC2 (F1×P2), F2, and F3 plants and evaluated for stomatal densities. Cut flowers of P1, P2, F1, BC1 (F1×P1), BC2 (F1×P2), and F3 were harvested after the first five flowers opened and evaluated for PHL. Additionally, cut flowers from these lines were evaluated for leaf surface area. Populations for evaluation were grown in the greenhouse in winter and spring 1999-2000 in a randomized complete-block design according to standard forcing procedures. Twenty-five cut flowering stems of each genotype were held in the laboratory in deionized water under continuous fluorescent lighting at 22 °C for PHL assessment. The end of PHL was defined as 50% of the flowers drying, browning, or wilting. Data will be presented on the correlation between stomatal density and PHL.

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Kenneth R. Schroeder and Dennis P. Stimart

Postharvest longevity (PHL) is important in determining quality and consumer preference of cut flowers; thus, it remains a pressing problem for the florist industry. Information on genetics and heritability of cut flower PHL is lacking. This study focused on determining gene numbers and inheritance of Antirrhinum majus L. cut flower PHL. An inbred backcross population was generated from a yellow short-lived (YS; 6d PHL) and a white long-lived (WL; 14 d PHL) inbred. F1 hybrids were backcrossed reciprocally three times to each parent. Parental backcross (BC) populations contained 55 to 65 lines. Lines within each BC generation were self-fertilized three generations by single-seed descent without selection to produce BC1S3, BC2S3, and BC3S3 generations. Cut flowers from all generations were evaluated together for PHL in deionized water. Gene numbers were estimated using confidence intervals and the proportion of non-parental BC lines. Continuous variation, estimates of a minimum of two to four genes controlling PHL, and significant environmental variation suggest selection for increased PHL would be successfu,l but slow. A negative correlation between PHL and yellow flower color was detected in this study. In spite of that fact, mean PHL of the yellow flowered inbred lines improved 1 to 2 d when backcrossing to YS and 3 to 4 d when backcrossing to WL without selection. Thus, inbred backcrossing to a long-lived parent with selection for flower color should make acquisition of longlived colored lines attainable.

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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

A phenol-sulfuric acid assay was used to quantify non-specific neutral carbohydrates in Antirrhinum majus L. flowering stems of three inbreds and their hybrids. Flowering stems 40 cm long were harvested with five to six florets open and flower, leaf, and stem tissue separated, freeze-dried, and finely ground. Carbohydrates were extracted from the tissue with 95% ethanol in a 70 °C water bath and combined with a 5% w/v phenol solution and concentrated sulfuric acid. Glucose equivalents were determined with a spectrophotometer at absorbance of 490 nm. Averaged over tissue type, results were genotype dependent, ranging from 213 to 291 μg glucose equivalent per mg dry tissue with a LSD0.05 = 13. Flowers had the highest concentration of 340 μg/mg dry tissue, followed by stems, then leaves with 36% and 38% lower concentrations, respectively. Carbohydrate concentrations in two inbreds were compared when grown under cool (16 °C) and warm (29 °C) conditions. A genotype x environment interaction exists with inbred 3 exhibiting no reduction, 6% increase, and a 45% reduction in carbohydrate concentration when grown in warm conditions, while inbred 2 exhibited 15%, 23%, and 37 % reductions for flowers, leaves, and stems, respectively. Overall, there were 10% and 21% reductions in carbohydrate concentration for inbreds 2 and 3, respectively, when plants were grown under warm conditions.

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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

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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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.