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Brent K. Harbaugh

Caladium × hortulanum Birdsey `Candidum' tubers were forced in pots until at least one-half the visible sprouts were 2 cm above the soil surface. These prefinished plants were subjected to simulated transit durations of 2, 4, or 6 days in the dark at 12.5, 15.5, 18.5, 21.0 or 24C. Plants were then grown for 4 weeks in a greenhouse and were either fertilized weekly with 100 ml of a solution containing 500 N-218P-415K (mg·liter-1) or were not fertilized. Interactive effects between transit duration and temperature were significant for all measured growth responses. Transit temperature maintained for 2 days had little effect on subsequent growth and only moderate effects after 4 days. With transit duration of 6 days, an increase in temperature resulted in increased plant height, fresh weight, number of leaves, white coloration of leaves, and percent of plants judged marketable (finished) in 4 weeks. Holding at ≈ 18.5C was most favorable for transit durations of 4 or 6 days. Use of fertilizer during finishing improved plant growth regardless of transit conditions, but did not totally negate deleterious effects from transit conditions.

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Brent K. Harbaugh

Symptoms of foliar chlorosis or bleaching, interveinal chlorosis of lower leaves, leaf edge and tip necrosis, stunted growth and delayed flowering of Eustoma increased as pH decreased below 6.5 in various peat-vermiculite based media for all cultivars tested. Symptoms were evident with or without microelement amendments in the media or fertilizer. A 5×5 factorial with pH of media and fertilizer solutions ranging from 5.1 to 7.5 indicated fertilizer pH did not negate plant response to low media pH. Leaf tissue levels of Zn were elevated at low media pH and negatively correlated to plant growth and flowering characteristics, while imbalances in tissue levels of N, P, K, Ca, Mg, Fe, Mn, Cu and B appeared to be less important. Symptomatic plants grown in media with a pH from 5.0 to 5.8 had tissue levels of Zn ranging from 200 to 1200 ppm, and plants without symptoms in media with a higher pH had leaf tissue levels from 40 to 100 ppm Zn.

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Brent K. Harbaugh

Rosetting response was determined for four lisianthus [Eustoma grandiflorum (Raf.) Shinn.] cultivars exposed to photoperiod and temperature treatments during stage 1(14 to 43 days after sowing) and stage 2 (43 to 79 days after sowing) seedling development. Stage 1 seedlings were exposed to short days (12 h photoperiod) or long days (18 h photoperiod) in combination with high (26C) or low temperatures (12C). After stage 1 treatments, stage 2 seedlings were divided and exposed to the same treatment combinations resulting in 16 treatments. Seedlings were then grown at 22C for 120 days to determine rosetting response. Cultivars responded differently to temperature and photoperiod. Short day-high temperature exposure during either stage 1 or stage 2 resulted in the greatest number of rosetted plants (50 to 100%) for `Yodel White', `HeidiPink', and `BlueLisa'. `GCREC-Blue' did not rosette with short day-high temperature. Low temperature during stage 1 did not prevent rosetting when stage 2 seedlings were subsequently exposed to high temperature, but low temperature during stage 2 decreased rosetting of seedlings exposed to high temperature in stage 1. Less rosetting occurred with long day-high temperature than with short day-low temperature, especially for `Blue Lisa'.

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Brent K. Harbaugh

Seedling growth and flowering responses were examined for four Eustoma cultivars exposed to photoperiod × temperature treatments during two seedling ages. Seedlings were grown under short days (SD, 12-hour photoperiod) or long days (LD, 18-hour photoperiod) in soil at 12 or 28C from 14 to 43 days after sowing. Seedlings from each treatment were then subdivided into four lots and subjected to the same photoperiod × temperature treatments from 43 to 79 days after sowing, for a total of 16 treatments. To determine flowering response, seedlings were grown subsequently for 120 days at 22C under the same photoperiod that they received from day 43 to 79. For all cultivars and both seedling ages, seedlings were larger and had more leaves when grown at 28C rather than at 12C, but the tallest plants at flowering were from seedlings exposed to 12C. Seedlings from some treatments bolted but did not initiate visible flower buds, and some seedlings developed visible buds that later aborted, resulting in plants that did not flower by the termination of the experiment (199 days). Cultivar and interactive effects of photoperiod and temperature influenced the percentage of flowering plants. Vegetative growth and flowering responses were similar for `Yodel White', `Heidi Pink', and `Blue Lisa'. They flowered as LD plants when seedlings were grown at 12C from day 14 to 43 or day 43 to 79. Seedlings of these cultivars that were grown under SD at 28C from day 43 to 79 did not flower, regardless of photoperiod or temperature treatments from day 14 to 43. However, SD photoperiod or 28C did not decrease flowering for `GCREC-Blue'.

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Zhanao Deng and Brent Harbaugh

Caladiums (Caladium×hortulanum) are ornamental aroids often forced in containers or grown in the landscape for their colorful leaves. The aesthetic value of caladium plants is largely determined by their leaf characteristics. Caladium breeding can be traced back to the mid-1800s when Gregor Mendel conducted his plant hybridization experiments, but information on the inheritance of caladium traits has been rather scant. To understand the mode of inheritance for three typical leaf shapes and three main vein colors in caladium, controlled crosses were made among commercial cultivars and breeding lines, and segregation of leaf shape and/or main vein color in the progeny was analyzed. The observed segregation ratios indicated that a single locus with three alleles seemed to determine the main vein color in caladium. The white vein allele was dominant over the green vein allele, but recessive to the red vein allele, which was dominant over both white and green vein alleles. The three leaf shapes (fancy, lance, and strap) in caladium seemed to be controlled by two co-dominant alleles at one locus. Leaf shape segregation was skewed in some crosses, which might imply the existence of other factors involved in caladium leaf shape development. Chi-square tests revealed that leaf shape and main vein color were inherited independently in caladium.

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Brent K. Harbaugh

Interveinal chlorosis of lower (oldest) leaves followed by development of interveinal necrotic spots, marginal necrosis, downward cupping of leaves, and leaf abscission were symptoms of a disorder commonly observed during production of potted pentas. The disorder was determined to be an Fe toxicity problem associated with accumulation of extremely high levels of foliar Fe (649 to 1124 ppm). Cultivars varied in their response to soil-applied Fe-DTPA chelate solutions: `Starburst', `Mauve' and `Ruby Red' were very susceptible, `Pink Profusion' was intermediate, and `White', `Lavender Delight', and `Pink Rose' were resistant. Potted plant production in a root medium with an initial pH of 6.7 ± 0.1 and a end pH of 6.4 ± 0.2 reduced the accumulation of foliar Fe to levels ranging from 59 to 196 ppm and prevented development of significant visual symptoms for all Cultivars.

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Zhanao Deng and Brent K. Harbaugh