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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

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.

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William J. Martin and Dennis P. Stimart

Narrow-sense heritabilities and genetic correlations of ornamental quality traits of Antirrhinum majus (snapdragon) were evaluated with special reference to cut flower postharvest longevity (PHL). Inbreds P1 (16 days PHL) and P2 (3 days PHL) were hybridized to produce an F1 (P1 × P2) that was self-pollinated to produce an F2 population. The F2 were self-pollinated to produce F3 families and advanced through single-seed descent by self-pollination to the F5 generation. P1, P2, F1, F3, F4, and F5 were evaluated for ornamental quality traits. Quality traits were found to be quantitative and normally distributed. Narrow-sense heritability (h2) estimates were high and consistent across generations examined; PHL h2 ranged from 0.79 to 0.81 ± 0.06. Phenotypic and genotypic correlations revealed underlying physiological and pleiotropic interactions relevant to breeding programs aimed at simultaneous improvement of ornamental quality traits. PHL is inversely related to cut flower strength and days to flower, -0.44 ± 0.04 and -0.43 ± 0.44. Buds at discard is positively correlated to cut flower and plant diameter, cut flower weight and days to flower, 0.77 ± 0.05, 0.58 ± 0.06, 0.71 ± 0.06, and 0.77 ± 0.07, respectively. Gain from selection for quality traits of interest can be rapid.

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Kenneth R. Schroeder and Dennis P. Stimart

Evaluation of leaf stomatal numbers and postharvest water loss indicate these are important factors in Antirrhinum majus (snapdragon) cut flower postharvest longevity (PHL). Cut flowers with 9 days longer PHL had 53% fewer leaf stomata. Long PHL is associated with an early reduction in transpiration followed by low steady transpiration. Short-lived genotypes had a linear transpiration pattern over the period of PHL indicating poor stomatal control of water loss. Short-lived genotypes had 22% to 33% reductions in fourth quarter transpiration while long-lived genotypes had 2% to 8% reductions. In addition, short-lived genotypes had higher average fourth quarter cut flower weight losses compared to long-lived genotypes. Further investigation of stomatal numbers and functioning relative to PHL may provide breeders a rapid and nondestructive indirect selection method for PHL.

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Wendy S. Higgins and Dennis P. Stimart

Lilium longiflorum Thunb. `Ace' bulblets generated in vitro at 25 or 30C were stored at 4C for O, 1, 2, 4, or 6 weeks after removal from culture and before planting to ascertain the effects of in vitro generation temperature and post-in vitro cold storage duration on bulblet growth responses during 36 weeks of greenhouse growth. Increasing post-in vitro storage duration decreased the number of days to first leaf emergence and percentage of plants producing shoots within 36 weeks, but increased the number of days to shoot emergence and anthesis, leaf number, and flower bud number. The length of time required for bulblet development from planting to shoot emergence was affected by storage duration more than periods from shoot emergence to visible bud and anthesis. It is feasible to produce high-quality L. longiflorum pot plants from in vitro-produced bulblets.

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James F. Harbage and Dennis P. Stimart

We investigated the role of ethylene on adventitious rooting of `Gala' (easy-to-root) and `Triple Red Delicious' (difficult-to-root) apple (Malus domestica Borkh.) microcuttings. Root count increased significantly as IBA level increased, with highest root counts on `Gala'. Ethylene evolution increased significantly with IBA level without significant differences between cultivars. Basal section removal of microcuttings in the area of root origin reduced root count without changing ethylene evolution. Ethylene treatment of proliferated shoots before microcutting excision failed to enhance rooting. IBA-induced ethylene evolution was eliminated nearly by AVG, but root count remained IBA dependent. ACC reversed IBA plus AVG rooting inhibition, but ACC alone failed to influence root count. Polar auxin transport inhibitors NPA and TIBA stimulated ethylene evolution without increasing root count. Adventitious rooting of apple microcuttings was not associated with ethylene. Chemical names used: 1-H-indole-3-butyric acid (IBA); aminoethoxyvinylglycine (AVG); 1-aminocyclopropane-1-carboxylic acid (ACC); 2,3,5-triiodobenzoic acid (TIBA); N-1-naphthylphthalamic acid (NPA).

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James F. Harbage and Dennis P. Stimart

Involvement of pH and IBA on adventitious root initiation was investigated with Malus domestica Borkh. microcuttings. The pH of unbuffered root initiation medium (RIM) increased from 5.6 to 7 within 2 days. Buffering with 2[N-morpholino] ethanesulfonic acid (MES) adjusted to specific pHs with potassium hydroxide prevented pH changes and resulted in a 2-fold higher root count at pH 5.5 compared to pH 7 or unbuffered medium. As pH decreased, lower concentrations of IBA were required to increase root counts. Colorimetric measurement of IBA in buffered RIM showed greater IBA loss and higher root count were associated with lower pH levels in all cultivars. This suggests that IBA loss from RIM depends on medium pH, which affects root count. Root count differences between easy-to-root through difficult-to-root cultivars were not consistent with amount of IBA loss from RIM. Cultivar differences in root count could not be explained solely by IBA loss from RIM.

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Joseph J. King, Lloyd A. Peterson, and Dennis P. Stimart

Ammonium and NO3 uptake from hydroponic solutions containing 1 mm each of (NH4)2SO4 and Ca(NO3)2 were measured during development of Dendranthema ×grandiflorum (Ramat.) Kitamura `Iridon', `Sequoia', and `Sequest'. Nitrogen depletion from solutions approximated a 1 NH4: 1 NO3 ratio throughout a 90-day growth cycle (r = 0.96). Although harvest date cultivar interactions were significant for both forms of N, overall patterns of N uptake were similar among cultivars. Nitrogen removal from hydroponic solutions (milligrams per plant) was greatest from days 40 to 60; however, N removal (milligrams per gram of tissue dry weight) was greatest in the first month of development and decreased steadily until day 90. From day 40 to 60, new leaf development ceased while inflorescence buds developed to ≈1.0 cm in diameter. After this time, N uptake decreased rapidly as inflorescences expanded. Correlations between morphological changes and N demand could maximize the efficiency of applied N by matching form and application timing with plant needs.

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Dennis P. Stimart, John C. Mather, and Kenneth R. Schroeder

Expanding shoot tips of Pulmonaria `Roy Davidson' and Pulmonaria saccharata `Margery Fish' were cultured in vitro on a modified Murashige and Skoog medium containing BA to establish proliferating cultures for use in comparing BA concentrations on shoot proliferation and rooting. The optimum level for shoot proliferation was 8.8 μm BA. Greatest rooting was on medium without BA. Genotype and time in culture influenced shoot and root counts. Chemical names used: N6-benzyladenine (BA)

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James S. Busse, Monica Figueroa-Cabanas, and Dennis P. Stimart*

Adventitious shoot formation in vitro from Antirrhinum majus L. hypocotyls was investigated using two inbred lines, the most and least regenerative lines selected from screening. Time course analysis indicated cell division in the most regenerative line occurred first in one or a small number of epidermal cells with periclinal and anticlinal divisions. Subsequently, cortical then vascular cells were recruited beneath the dividing epidermal cells. Once shoots formed, their vascular system was continuous with the original hypocotyl explant. The least regenerative line had no cell division directed toward organogenesis. Shoot formation on hypocotyls of A. majus was adventitious in origin, by direct organogenesis and genotype dependent.