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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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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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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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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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Dennis P. Stimart and John C. Mather

Actively growing shoots from Pulmonaria L. `Roy Davidson' were cultured in vitro on Murashige and Skoog medium containing benzyladenine (BA) to establish proliferating cultures. BA at 0, 0.4, 0.8, 4.4, 8.8, and 44.4 μm was compared for shoot proliferation and rooting response. Shoot count was highest on 8.8 μm BA with root count highest on 0 or 0.4 μm BA. Subculture 4 weeks later of shoots to the same treatments resulted in highest shoot counts on 44.4 μm BA. Optimum level for micropropagation was 8.8 or 44.4 μm BA. Greatest rooting was at 0 or 0.4 μm BA.

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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

Efforts to improve postharvest longevity of fresh-cut flowers has only recently turned toward selection and breeding. Conventional methods to extend keeping longevity of cut flowers depend on use of chemical treatment placed in holding solutions. Postharvest longevity studies were initiated with Antirrhinum majus L. (snapdragon) to determine: if natural genetic variation existed for cut-flower longevity, the inheritance of the trait, heritability, and associated physiology. Evaluation of commercial inbreds held in deionized water revealed a range in cut-flower longevity from a couple of days to 2.5 weeks. The shortest- and longestlived inbreds were used as parents in crosses to study the aforementioned areas of interest. Information will be presented on inheritance of cut flower longevity based on populations evaluated from matings for generation means analysis and inbred backcross method. Also presented will be information on stomata, transpiration, carbohydrate, fresh-weight change, and forcing temperature relative to postharvest longevity.

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Kenneth R. Schroeder and Dennis P. Stimart

Hypocotyls from Antirrhinum majus L. were excised at 2 weeks of age from seedlings grown under a 16-hour photoperiod or continuous darkness. Explants were cultured on modified Murashige-Skoog (MS) medium containing 0, 0.44, 2.22, 4.44, 8.88, or 44.4 μm BA to investigate adventitious shoot formation. Excised hypocotyls from eight commercial cultivars, three inbred lines, and an F1 hybrid between two of the inbreds were cultured on MS medium containing 2.22 μm BA to assess genotypic effects on adventitious shoot formation. The influence of seedling age was assessed by excising hypocotyls from seedlings at 6, 10, 14, 18, 22, 26, or 30 days. Optimal conditions for adventitious shoot formation on excised hypocotyls included: seedling growth in a lighted environment, use of hypocotyls from 10-day-old seedlings, and culture on medium containing 2.22 μm BA for 3 weeks. Under these conditions, up to a 5-fold improvement in number of shoots per hypocotyl over previous studies was achieved. Adventitious shoot formation was genotype-dependent and appeared to be a dominant trait. Chemical name used: N 6-benzyladenine (BA).

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Dennis P. Stimart and William J. Martin

The time required to maintain plants on a standardized basis (effort) was investigated in 24 gardens of various plant composition over 5 years. Cluster analysis of data grouped gardens into five clusters based on magnitude and timing of effort. Plants grown in containers required up to 20 times more effort annually than plants grown in other gardens in ground beds. Gardens planted with annuals required about 80% less effort than container gardens but 75% more effort than other gardens evaluated. As the number of taxa in gardens decreased, effort decreased and was less variable throughout the year. Enumeration of effort in relation to garden composition should be used to project management cost for gardens.