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Brent K. Harbaugh, John W. Scott, and David B. Rubino

Seedlings of commercial lisianthus cultivars form rosettes when grown at 25 to 28°C. Rosetted plants have a basal cluster of leaves, very short internodes typical of biennials, and do not bolt or flower for months without being exposed to 3 to 4 weeks at <15 to 18°C to reverse heat-induced rosetting. Semirosetted plants develop when seedlings are grown at a constant 22 to 25°C or at <22°C night with >28°C day. Semirosetted plants have one or more side shoots which may elongate and flower, but plants flower unpredictably and are of poor quality as cut flowers or potted plants. `Maurine Blue' and Florida Blue' were released from the Univ. of Florida in 1995. To our knowledge, they are the first heat-tolerant lisianthus cultivars. Seedlings and plants can be grown at 28 to 31°C without rosetting. `Maurine Blue' ranged in height from 38 cm (summer) to 67 cm (spring) during 1994 and 1995 production trials in Florida. `Maurine Blue' has potential for use as a tall bedding plant if sold as green transplants, a flowering potted plant if grown with three plants per 15-cm-diameter pot with a growth retardant, or as a bouquet-type cut flower. `Florida Blue' plants (38 cm) grown in an 11.5-cm square pot (0.65-L) with capillary mat irrigation were similar in height to `Blue Lisa' (32 cm) and taller than `Little Belle Blue' (22 cm) and `Mermaid Blue' (24 cm). `Florida Blue' was designated as a semi-dwarf cultivar with an intended use as a bedding plant. Growth retardants would be useful for production in pots <10 to 12 cm in diameter. Complete descriptive information, photographs and pedigrees will be presented.

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Brent K. Harbaugh, Michelle L. Bell, and Rongna Liang

Lisianthus [Eustoma grandiflorum (Raf). Shinn.] is emerging as an important cut flower in the United States while in European and Asian markets it is already listed among the top ten cut flowers. Many new cultivars have been released in the United States within the last 5 years, but comparative performance trials of these cultivars have been lacking. This trial evaluated 47 cultivars of lisianthus representing series (cultivar groups) that were marketed in the United States in 1998. Evaluations were made for rosetting, plug performance, cut-flower characteristics (vegetative and flowering attributes) as well as postharvest longevity of cut flowers. Significant differences among cultivars were found for all of the attributes evaluated. `Malibu Purple', `Catalina Blue Blush', and `Alice Pink' were selected as the best performers in the seedling (plug) stage since they had less than 5% rosettes, large leaves and a vigorous root system. Cultivars were placed in classes based on flower color, flower size, and number of petals (single or double flowers). Cultivars were ranked for each of the attributes and the total rank sum of all attributes (TRS) was used to select the best in class. Cultivars selected as best in class were `Malibu Purple', `Malibu Blue Blush', `Alice Purple', `Balboa Blue', `Avila Blue Rim', `Mellow Pink', `Flamenco Wine Red', `Flamenco Rose Rim', `Alice Pink', `Avila Rose' and `Echo Pink', `Alice White', and `Mariachi White'.

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Brent K. Harbaugh, Mark S. Roh, Roger H. Lawson, and Brent Pemberton

Three lisianthus [Eustoma grandiflorum (Raf.) Shinn.] cultivars 0, 10, 17, 24, or 31 days from sowing were grown in 28C soil for 0, 7, 14, 21, or 28 days to determine the effects of high temperature during seedling growth on the development of rosetted plants. Increasing the duration of high-temperature exposure increased the percentage of rosetted plants for all cultivars. Such exposure for 28 days resulted in 96%, 93%, and 18% rosetted plants for cultivars Yodel White, Yodel Pink, and GCREC-Blue, respectively. Seedling age did not affect percentage of flowering `Yodel Pink' plants, but as seedling age increased to 31 days, the percentage of flowering plants increased with `GCREC-Blue' and decreased for `Yodel White'. In a second experiment, four lisianthus cultivars were grown at 22C for 3 weeks and then exposed for 28 days to soil at 22, 25, 28, or 31C. Increasing soil temperature resulted in more rosetted plants for all cultivars. With soil at 31C, 83%, 58%, 19%, and 2% of the seedlings rosetted for the cultivars USDA-Pink, Yodel White, Little Belle Blue, and GCREC-Blue, respectively.

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Richard O. Kelly, Zhanao Deng, Brent K. Harbaugh, and Rick K. Schoellhorn

Florida is one of the top wholesale producers of bedding plants, and in 2003 was ranked fourth in annual bedding plant production and fifth in potted pansy/viola production. Evaluation of pansy cultivars is vital for continued growth of the industry. We evaluated 210 cultivars of pansy (Viola ×wittrockiana) (164 new cultivars) in replicated class tests at the University of Florida's Gulf Coast Research and Education Center at Bradenton, Fla., from 2000–04 to determine the best-of-class and use them in future trials to compare against new entries in the same class. In this report, we provide objective plant measurements of vegetative and floral characteristics as well as subjective performance ratings. Subjective ratings were on a 1 to 7 scale with the highest rating of 7 for excellent. In general, overall performance ratings (combined foliage, flower, arthropod, and disease ratings) ≥5.5 were considered outstanding. Pansy cultivars were grouped into classes based on flower color and pattern. Best-of-class selections that had an outstanding overall performance rating in one or more contested trials, never falling below 5.0 in other contested trials, were: (black class) `Accord/Banner Black Beauty', (blue shades/tints class) `Nature Blue', (blue with blotch class) `Nature Ocean', (mix class) `Panola Clear Mixture', (pink shades/tints with blotch class) `Nature Pink Shades', [purple (dark), blue-violet with white cap class] `Nature Beacon', [purple (dark), blue-violet/white face with blotch class] `Panola Purple With Face', (purple with light eye class) `Baby Bingo Lavender Blue', (white class) `Nature White', (yellow class) `Nature Yellow', (yellow with blotch and purple, blue-violet cap class) `Iona Purple & Yellow With Blotch', (yellow with blotch and red cap class) `Bingo Red & Yellow', (yellow with blotch and red cap class) `Panola Yellow With Blotch', (yellow with dark veins class) `Whiskers Yellow'. We believe these cultivars would perform well in the southern U.S. or areas of the world with similar heat and cold hardiness zones.

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Fahrettin Goktepe, Zhanao Deng, Brent K. Harbaugh, Teresa Seijo, and Natalia A. Peres

Caladiums, widely used in containers and landscapes as ornamental plants for their bright colorful leaves, are generally forced or grown from tubers. Commercial production of these tubers in central Florida is through dividing “seed” tubers and growing them in fields. Tuber quality is therefore of critical importance to success in container forcing, landscape use, and tuber production. Fusarium tuber rot (Fusarium solani) has been recognized as the most-destructive disease that affects caladium tuber quality. There is anecdotal evidence from growers indicating the existence of resistance in commercial caladium cultivars. To identify and confirm the source of fusarium tuber rot resistance in caladium, F. solani isolates have been collected from rotting tubers grown under different soil conditions and from different locations. The pathogenecity of these isolates has been tested through artificial inoculation of fresh harvested and/or stored tubers, and a number of highly virulent isolates have been identified. These isolates have been used to refine inoculation and disease evaluation techniques. Two techniques, spraying a conidial suspension onto fresh cut surfaces and inserting Fusarium-infested carnation leaf segments into artificial wounds, have proven to yield consistent resistance/susceptibility ratings among cultivars of known difference in resistance to fusarium tuber rot. Appropriate incubation temperatures and humidity seem to be very critical for disease development and evaluation. The two techniques have been used to evaluate 35 cultivars. Several cultivars, including `Candidum', showed a high level of resistance to fusarium tuber rot, and may be good breeding parent for developing new resistant cultivars.

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Yan Chen, Kimberly A. Williams, Brent K. Harbaugh, and Michelle L. Bell

Host-plant nutritional status may affect the incidence and development of western flower thrips (WFT; Frankliniella occidentalis Pergande). Two greenhouse experiments were conducted to determine the responses of WFT population levels on impatiens (Impatiens wallerana Hook.f.) when plants were fertilized with commercially practiced rates of nitrogen (N) and phosphorus (P). Impatiens `Dazzler Violet' were grown with nutrient treatment combinations of 2 N rates (8 and 20 mm) by 2 P rates (0.32 and 1.28 mm). Individual plants grown in thrips-proof cages were inoculated with WFT at 2 or 4 weeks after transplant, in separate experiments, representing vegetative or reproductive stages of plant growth, respectively. Plants were destructively sampled weekly for 4 weeks following inoculation. Plant tissue N and P concentrations were significantly different across treatments: 8 and 20 mm N resulted in 4.9% and 6.3% N in tissue, respectively; 0.32 and 1.28 mm P resulted in 0.37% and 0.77% P in tissue, respectively. Nitrogen rates had no effect on WFT population levels. However, 4 weeks after inoculation with adult female WFT during the vegetative growth stage, plants fertilized with 1.28 mm P had more adult WFT than those fertilized with 0.32 mm P. Feeding damage varied depending on whether plants were inoculated in the vegetative stage with adult WFT or during reproductive growth with immature WFT. Plant size and number of flowers were lower in plants inoculated during the vegetative growth stage with adult WFT but were not affected when inoculation with immature WFT occurred during the reproductive stage, as most WFT were found feeding inside the nectariferous spurs of the flowers. Tissue N was lower in WFT-inoculated plants compared to noninoculated plants in both experiments.

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Amy L. Shober, Christine Wiese, Geoffrey C. Denny, Craig D. Stanley, Brent K. Harbaugh, and Jianjun Chen

Recent concerns over the environmental impact of peat harvesting have led to restrictions on the production of peat in Florida and other areas. The objectives of this study were to evaluate the use of composted dairy manure solids as a substitute for sphagnum or reed-sedge peat in container substrates on the growth of Solenostemon scutellarioides L. Codd ‘Wizard Velvet’, Tagetes patula L. ‘Safari Queen’, and Begonia ×hybrida ‘Dragon Wing Red’ and to examine the nutrient content in leachate from pots. Plants were grown for 5 weeks in a greenhouse in 15-cm plastic pots with seven substrates containing various proportions of sphagnum peat (S) or reed-sedge peat (R) and composted dairy manure solids (C), each with 20% vermiculite and 20% perlite. Substrate composition had no effect on plant quality ratings, number of flowers, or root dry mass for any of the plant species evaluated. Substrate composition did not affect the growth index (GI) or shoot dry mass of S. scutellarioides ‘Wizard Velvet’ or the GI of T. patula ‘Safari Queen’. However, growth of B. ×hybrida ‘Dragon Wing Red’ (GI and shoot dry mass) and T. patula ‘Safari Queen’ (shoot dry mass only) was highest in the 3S:0R:0C substrate. The substrates containing sphagnum peat and/or composted dairy manure solids (3S:0R:0C, 2S:0R:1C and 1S:0R:2C) had the highest NH4-N losses through the first 7 d of production. The 0S:3R:0C substrate had the highest initial leachate NO3+NO2-N losses and this trend persisted throughout most of the production cycle. Significantly more dissolved reactive phosphorus was leached from substrate mixes containing composted dairy manure solids than mixes containing only sphagnum or reed-sedge peat materials through 19 d after planting. All substrates tested as part of this study appeared to be commercially acceptable for production of container-grown bedding plant species based on plant growth and quality. However, nutrient losses from the containers differed depending on the peat or peat substitute used to formulate the substrates.

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Zhanao Deng, Jinguo Hu, Fahrettin Goktepe, Brady A. Vick, and Brent K. Harbaugh

Cultivated caladiums are valued for their bright colorful leaves and are widely used in containers and landscapes. More than 1500 named cultivars have been introduced during the past 150 years, yet currently only about 100 cultivars are in commercial propagation in Florida. Caladium tubers produced in Florida account for 95% of the world supplies. Loss of caladium germplasm or genetic diversity has been a concern to future improvement of this plant. In addition, the relationship among the available cultivars, particularly those of close resemblance, has been lacking. This study was conducted to assess the genetic variability and relationship in commercial cultivars and species accessions. Fifty-seven major cultivars and 15 caladium species accessions were analyzed using the target region amplification polymorphism marker technique. This marker system does not involve DNA restriction or adaptor linking, but shares the same high throughput and reliability with the amplified fragment length polymorphism system (AFLP). Eight primer combinations amplified 379 scorable DNA fragments among the caladium samples. A high level of polymorphism was detected among the species accessions as well as among cultivars. These markers allowed differentiation of all the cultivars tested, including those hardly distinguishable morphologically. Clustering analysis based on these DNA fingerprints separated the cultivars into five clusters and Caladium lindenii far from other caladium species. The availability of this information will be very valuable for identifying and maintaining the core germplasm resources and will aid in selecting breeding parents for further improvement.

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Zhanao Deng, Brent K. Harbaugh, Rick O. Kelly, Teresa Seijo, and Robert J. McGovern

Caladiums (Caladium ×hortulanum) are widely grown as pot or landscape plants for their attractive leaves. Pythium root rot (Pythium myriotylum) is one of the most damaging diseases in caladium, severely reducing plant growth, aesthetic value, and tuber yield. Twenty-three commercial cultivars were inoculated with three aggressive isolates of P. myriotylum and evaluated for their resistance to root rot. Three cultivars, `Apple Blossom', `Blizzard', and `Etta Moore', were found to have a moderate level of resistance (partial resistance) to pythium root rot. The rest of these cultivars were susceptible or highly susceptible to Pythium infection, losing up to 94% of their root tissue to rotting within 10 days after inoculation. Data indicated a linear relationship between root rot severity and leaf loss severity on Pythium-inoculated plants and highlight the importance of controlling pythium root rot in caladium pot plant and tuber production. Comparison of some recent releases with their parents for pythium root rot resistance suggests the potential of developing new resistant caladium cultivars using the identified sources of resistance.

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Zhanao Deng*, Brent K. Harbaugh, Rick Kelly, Teresa Seijo, and Robert J. McGovern

Caladiums (Caladium × hortulanum) are widely grown for their bright colorful leaves. Pythium root rot, caused primarily by P. myriotylum, is one of the most important diseases in caladiums. This disease can dramatically reduce plant growth, impact plant aesthetical value, and lower tuber yield. Pythium infection in the roots may also lead to subsequent entry of Fusarium into tubers resulting in tuber rot. There has been a strong interest in the tuber production and greenhouse plant production industries to identify cultivars that are resistant or tolerant to Pythium. However, few studies have been conducted since the pathogen was identified, and little information is available regarding the existence of any possible resistance in commercial cultivars. Pythium isolates were made from diseased plants collected from different sites; their pathogenicity was confirmed using tissue culture-derived plants. Procedures were developed for oogonia spore production, inoculation, and disease severity assessment. Nineteen major commercial cultivars were inoculated at two spore densities and then maintained in greenhouses under growing conditions favorable for root rotting. Plant appearance, leaf characteristics and severity of root rotting were evaluated 2-3 times after inoculation. Observations indicated that the isolates were highly virulent. They induced visible root rot within 3-5 days, and caused a complete loss of the root system and plant death for some cultivars within 2-3 weeks after inoculation. Several cultivars, including `Candidum' and `Frieda Hemple' which are widely grown cultivars, had much less root rot, higher plant survival, and seemed to have moderate levels of resistance.