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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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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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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

One-centimeter hypocotyl explants from 2-week-old Antirrhinum majus L. (snapdragon) seedlings germinated and grown in vitro under 12-h cool-white fluorescent light and 12 h dark or 24 h dark were placed on Murashige and Skoog (MS) medium containing 0, 0.44, 2.22, 4.44, 8.88, or 44.4 μM N6-benzyladenine (BA). Cultures were maintained under the light/dark regime at 25°C. After 2 weeks, adventitious shoots were counted. A shoot was considered adventitious and counted if a stem and leaf developed. Shoots developed along the entire length of the hypocotyl sections. Mean shoot production per hypocotyl explant ranged from 2.4 to 6.1 shoots when seedlings were germinated and grown in 24 h darkness and 2.2 to 10.9 shoots when started in the light/dark regime. Highest shoot counts were attained /from hypocotyl explants when seedlings were germinated and grown under the light/dark regime for 2 weeks and transferred to 2.22, 4.44, or 8.88 μM BA. Shoot development appeared normal at the 2.22 and 4.44 μM level, while at 8.88 μM BA, development was slightly abnormal along with slightly more callus production.

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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

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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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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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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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.

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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.