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Jack W. Buxton, Donna Switzer and Guoqiang Hou

Marigold seedlings, 3 weeks old, were grown in natural light growth chambers at 3 day/night temperature regimes, 8°N/16°D, 13°N/20°D and 18°N/24°D, in a factorial combination with ambient and 1000-1500 ppm CO2. Seedlings were harvested at regular intervals during a 24 hr period and were analyzed for soluble sugars (reducing sugars and sucrose) and starch. Neither temperature nor CO2 concentration affected the accumulation of soluble sugars or starch during the day or night. The soluble sugar concentration ranged from 3% of dry weight at sunrise to 6% at mid-day; the concentration changed little during the night. Light intensity was different during replications of the experiment. Increased light intensity appeared to cause a slight increase in the soluble sugars maintained by the seedling during the day. Accumulated starch increased 6% to 8% from sunrise to late afternoon. Preliminary results indicate that light intensity greatly affected the concentration of starch. On the higher light intensity day, starch accumulated to a maximum of 18% of dry weight; whereas on the lower light intensity day the maximum concentration was 10%. During the night following the lower light intensity day, the starch concentration decreased to approximately 3% by the end of the night; following a brighter day the starch content was 13% at the end of the night.

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Guoqiang Hou, Jack W. Buxton and Michael Collins

Studies were conducted to determine if near infrared reflectance spectrophotometry (NIR) could be used to rapidly determine nonstructural carbohydrate (TNC) concentrations in marigold tissue. Marigold seedlings were grown in natural light growth chambers. Light intensity and CO2 concentration were adjusted to establish leaf samples with a wide range of the carbohydrate concentration. NIR spectra were collected on dry, ground samples using a reflectance scanning monochromator. Conventional laboratory analysis values for the same samples were correlated with spectral data. Calibration statistics were as follows: TNC; standard error of calibration (SEC)= 1.73, R2= 0.95, standard error of prediction or perfomance (SEP) = 1.64, R2= 0.95; Starch, SEC = 1.35, R2= 0.96, SEP = 1.37, R2= 0.94; Soluble Sugars, SEC = 0.26, R2= 0.91, SEP = 0.29, R2= 0.84. These results show that the NIR method can be used to rapidly determine concentrations of nonstructural carbohydrates in marigold leaf tissue and suggest the possibility for routine assessment of carbohydrate status for optimum management of environmental factors.

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Jennifer Marohnic, Robert Geneve and Jack W. Buxton

Capillary mats were used to vary the water content in oasis blocks during mist propagation of chrysanthemum cuttings. Mats placed on the surface of the propagation bench extended over the edge of the bench and downward a distance of either 0 or 20 cm. Oasis blocks with chrysanthemum cuttings `Boaloi' and `Salmon Charm' were placed on mats under intermittent mist (10 seconds every 5 minutes) between 5 am and 8 pm. Relative water content, mL of water/gram oasis, and leaf water potential were measured at noon every 5 days. After 26 days number of roots per cutting was evaluated. Water content in the oasis block was reduced by 49% (450 to 219 mL/g dry weight of oasis) by hanging the capillary mat 20 cm over the edge of the bench compared to 0 cm treatment. Cuttings showed an increase in leaf relative water content from 49% and 51% at day 1 to 65% and 71% by day 11 for `Boaloi' and `Salmon Charm', respectively. Following initial root formation, leaf relative water content increased to 85%. Over the course of the experiment `Boaloi' and `Salmon Charm' showed an average reduction in leaf water potential of 0.14 and 0.08 MPA, respectively. `Boaloi' showed overall higher root numbers than `Salmon Charm'; however, no difference in rooting between mat treatments was observed.

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Robert L. Geneve, Jack W. Buxton and Myra Stafford

Capillary mat subirrigation provides uniform water in the growing medium to optimize seedling growth in plugs. It also offers a closed system that allows the grower to regulate the amount of water available to seedlings and to reduce water runoff. However, root outgrowth into the capillary mat can be a significant problem. Copper hydroxide (Spin Out) was painted on the bottom, outside surface of the plug container to control root outgrowth into the capillary mat. Three square and two octagonal plug sizes were treated with copper. Regardless of the plug size or shape, copper treatment was an effective treatment to control root outgrowth in marigold seedlings. Copper treatment reduced overall root outgrowth by 80% to 92%. Marigold and geranium seedlings in copper-treated square plug containers showed some reduced shoot and root development during plug production, but there were no differences in copper-treated plants compared to nontreated plants following transplanting to cell packs.

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Myra Stafford, Robert L. Geneve and Jack W. Buxton

This study evaluated the effect of container shape and copper hydroxide on root and shoot development of marigold (Tagetes patula `Little Devil Flame') seedlings. Containers were modified in shape and volume by gluing triangular polycarbonate inserts vertically onto sides of the container. The inserts were either painted with copper or not painted. Inserts decreased container volumes (no insert = 480 cm3, two inserts = 340 cm3, and four inserts = 200 cm3). After 38 days the seedling roots were scanned for computer analysis, and leaf area and dry weights were determined. Copper effectively prevented roots from growing in contact with copper treated surfaces. Shoot dry weight and leaf area were greater with no inserts, but if inserts were treated with copper the shoot dry weight and leaf area were greater. Root dry weight was reduced 7%–10 % with two inserts and 20% with four inserts compared to no inserts. Copper treated inserts reduced the dry weight further. However, at the insert interface, root length was increased between 15%–20% by all copper treatments, with the greatest increase in the four-insert treatment.