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Brent K. Harbaugh, David A. DeVoll, and R. Zalewski

Phosphorus is considered a major pollutant of lakes in central Florida, and growers producing crops in the Lake Okeechobee watershed are being challenged to reduce use of P fertilizer. Caladium (Caladium×hortulanum Birdsey) tubers are produced on organic soils within this area. This study was done to determine if current commercial P fertilization rates could be reduced or eliminated, since these organic soils have high levels of water extractable P (Pw). Two farms were selected with low (Farm A 19 lb/acre; 21 kg·ha-1) or high (Farm B 59 lb/acre; 66 kg·ha-1) preplant Pw levels. Production of caladium tubers with the standard grower P fertilization practice (Farm A = P at 39.2 lb/acre; 43.9 kg·ha-1, or Farm B = P at 15.9 lb/acre; 17.8 kg·ha-1) was compared to production with either one-half the standard grower rate of P or no P. The percentage of harvested tubers in each of five grades and the estimated harvested tuber value index were similar irrespective of the amount of P fertilizer used on either farm. These results indicate that P could be eliminated from the fertilization program for caladium tuber production on organic soils.

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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.

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J. P. Gilreath and B. K. Harbaugh

Abstract

Eight herbicides were evaluated for phytotoxicity to field grown ‘Candidium’ caladiums (Caladium × hortulanum Birdsey) in 1983. The 4 most promising or currently used herbicides were evaluated for weed control and phytotoxicity in 1984. During 1984, 4 applications of 2.24 kg/ha alachlor, 2.24 kg/ha simazine, 1.68 kg/ha oryzalin, and 0.56 kg/ha oxyfluorfen, all in combination with 1 postemergence application of 0.28 kg/ha fluazifop-butyl, were applied to caladiums. Alachlor and oxyfluorfen provided poor weed control and reduced plant vigor, tuber weights, and tuber size in 1984. Simazine provided good weed control, but reduced plant vigor and yield. Oryazlin provided excellent weed control without crop injury. Chemical names used: 2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide (alachlor); 6-chloro-N,N’-diethyl-1,3,5-triazine-2,4-diamine (simazine); 4-(dipropylamino)-3,5-dinitrobenzene sulfonamide (oryzalin); 2-chloro-l-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene (oxyfluorfen); butyl-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoate (fluazifop-butyl).

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Eakhlas U. Ahmed, Takahiro Hayashi, and Susumu Yazawa

The developmental pattern of leaf color distribution during plant development in 10 cultivars of Caladium ×hortulanum Birdsey was investigated. We used the color occupying the largest area in the terminal leaf as the dominant color, and expressed the leaf color stability during plant development by the ratio of the percentage of the dominant color area in the terminal leaf to that of the dominant color area in the initial leaf (leaf color stability index). In some cultivars, leaf color stability index was clearly greater than 1 (leaf-color-unstable cultivar), but in some cultivars it was close to 1 (leaf-color-stable cultivar). In plants regenerated from leaf explants of leaf-color-unstable cultivars, many (21% to 43%) color variants were observed but only a few (0% to 6%) occurred from leaf explants of leaf-color-stable cultivars. Tissue culture appears to be a useful technique for rapid propagation based on leaf color stability in leaf-color-stable and leaf-color-unstable cultivars.

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William R. Woodson and Timothy J. Raiford

Abstract

Storage of Caladium × hortulanum L. tubers at 5°C for 1 to 3 weeks resulted in an elevation in CO2 production when transferred to 22°. A decrease in storage temperature from 22° to 1° resulted in an increase in respiratory activity following transfer of tubers to 22°. The respiratory burst associated with low temperature storage was greatest following 24 hr at 22°, after which a decline in CO2 production was seen. Electrolyte leakage from ‘Carolyn Whorton’ tuber disks increased when tubers were held for either 3 weeks at 5° or 2 weeks at 1°, as compared to shorter durations of chilling or higher temperatures. Sprouting (days to emergence) of planted tubers was delayed following low temperature storage, as compared to tubers held at 22°. Although delayed, all tubers sprouted when held a maximum of 3 weeks at 5°, or 2 weeks at 1°.

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Zhanao Deng and Brent K. Harbaugh

As a common pot and landscape plant, caladium ( Caladium ×hortulanum Birdsey, Araceae Juss.) is valued for its colorful leaves and low maintenance requirements ( Evans et al., 1992 ). Commercial caladium plants are grown from tubers. Central

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Brent K. Harbaugh

Florida Agricultural Experiment Station Journal Series no. R-00063. Appreciation is extended to Bates & Sons Caladiums, Lake Placid, Fla., for supplying plant material and partial funding for this project. The cost of publishing this paper

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Michael R. Evans and Brent K. Harbaugh

published as Florida Agricultural Experiment Station journal series R-03045. We thank Happiness Farms and Bates and Sons Caladiums for financial and material support of this project. Use of trade names does not imply endorsement of the

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William J. Carpenter

Caladium hortulanum Birdsey cv. Candidum seed failed to germinate without light; maximum germination required daily, incandescent light of ≤4 hours. Lengthening daily lighting periods progressively reduced the days to 50% relative germination (T50) from 20 to 8, and days between 10% and 90% relative germination (T90 – T10) from 16 to 5. T50 and T90 – T10 were shortest (≈ 8 days) at 25 and 30C, while total or absolute germination percentage (G) was highest at ≈ 90%. G was 94% for seeds harvested immediately, but 75% or 38% for seeds that remained in fruits for 3 or 12 weeks after fruit abscission from the spadix. Total absolute germination was reduced from 95% to 87% when seed moisture contents declined to <14%. Seed storage for 7 days at from 10 to – 80 C-caused no reduction in G. Seeds were stored 6 months at 15C and 22%, 33%, or 52% RH without change in G, but storage at 5 or 25C and 11%, 75%, or 95% RH significantly reduced germination.

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James E. Barrett, Carolyn A. Bartuska, and Terril A. Nell

Paclobutrazol drench treatments were evaluated for efficacy on Caladium ×hortulanum (Birdsey) cultivars Aaron, White Christmas, and Carolyn Wharton. Drenches at 2.0 mg/pot did not reduce height of `Aaron' and `White Christmas' plants when applied 1 week after planting, but 2.0 mg applied at 3 weeks after planting did result in shorter plants. The difference for time of application may be due to the amount of roots present to take up paclobutrazol when applied. In two factorial experiments, there were no interactions between cultivar and time of application or amount of chemical. Paclobutrazol at 0.5 mg/pot resulted in plants that were shorter than the controls. Higher amounts of paclobutrazol provided additional reductions in height, but there was variation between the experiments for degree of effect with amounts >1 mg. Generally, commercially acceptable height control was provided by paclobutrazol drench treatments at 0.5 and 1.0 mg/pot applied 3 weeks after planting. Chemical names used: (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-1,2,4-triazol-1-yl-pentan-3-ol (paclobutrazol).