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Dinum Perera and Brian W. Trader

Milky sap (latex) secreted at the cut surfaces is a common feature of the family Euphorbiaceae; the genus Euphorbia consists of close to 2000 species ( Ecke et al., 2004 ). Euphorbia pulcherrima Willd. ex Klotzsch, poinsettia, belongs to

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Diane M. Camberato, Roberto G. Lopez and Brian A. Krug

Langhans, R.W. Larson, R.A. 1960 Influence of day length, temperature, and the number of short days on the flowering of poinsettia ( Euphorbia pulcherrima ) Proc. Amer. Soc. Hort. Sci. 75 753 760 Langton, A. Plackett, C. Kitchener, H. 2006 Energy saving in

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Dewayne L. Ingram, Charles R. Hall and Joshua Knight

Euphorbia pulcherrima (poinsettia) annually ( USDA-NASS, 2016 ). This model enterprise grew ≈32,000 pots in 2015; they were sold at an average price of $4.94 if grown in pots 12.7-cm or larger ($2.14 for those grown in pots smaller than 5 inches). Profit

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James N. Smith and Michael R. Evans

Vegetative 6-cm Euphorbia pulcherrima `Freedom' cuttings were placed in black 200-ml bottles containing humic acid solutions, nutrient solutions, or deionized water. Humic acid solutions were prepared using Enersol SC (American Colloid, Arlington Heights, Ill.). Concentrations of 500, 750, and 1000 mg/L humic acid were compared to solutions containing mineral element concentrations equivalent to those contained in humic acid solutions. After 4 weeks, 88%, 75%, and 88% of cuttings had rooted in the 500, 750, and 1000 mg/L humic acid solutions, respectively. Cuttings placed in nutrient controls or deionized water failed to form roots after 4 weeks. Average root fresh mass was 175, 80, and 72 mg for cuttings placed in 500, 750, and 1000 mg/L humic acid solution, respectively. Average number of roots formed per cutting ranged from 21 in the 500-mg/L solution to 6 in the 1000-mg/L solution. Average lengths ranged from 26 mm in the 500-mg/L to 12 in the 1000-mg/L solution. As humic acid concentration increased, average root fresh mass, average number of roots, and the length of the longest root significantly decreased.

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Joaquin A. Chong, Uttara C. Samarakoon and James E. Faust

poinsettia cuttings. Materials and Methods Poinsettia ( Euphorbia pulcherrima Willd. ex. Klotsch) ‘Freedom Red’ unrooted cuttings were propagated on 18 Sept. and 9 Jan. with one cutting per pot in 771-cm 3 square pots, 12.7 cm tall and 8.9 cm wide (TLC

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Mogens Nicolaisen

Phytoplasma PoiBI is responsible for free branching in poinsettia (Euphorbia pulcherrima Wild. ex. Klotzsch). In this study, PoiBI was transmitted by dodder from poinsettia to crown-of-thorns (E. milii Des Moulins) in one out of ≈100 attempts, whereas grafting transmission was unsuccessful. PoiBI was shown to be viable in E. milii, as it was detected in the recipient plant and in its cuttings over 1.5 years by polymerase chain reaction. It was shown that PoiBI induces free branching in E. milii as well as in poinsettia. Smaller leaves, reduced growth rates, and delayed flowering were other effects of PoiBI infection.

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Michael R. Evans and Andrew A. Waber

Euphorbia pulcherrima `Freedom' (poinsettia) and Pelargonium ×hortorum `Pink Elite' (geranium) were grown in 75:25:0, 50:50:0, 27:75:0, 75:0:25 50:0:50, 25:0:75 (v/v sphagnum peat: 0.25-grade rubber: 0.10-grade rubber) substrates or in a 50 sphagnum peat: 30 perlite: 20 loam (v/v) standard greenhouse substrate. Geranium root and shoot fresh weights, height, and number of axillary shoots were reduced when grown in rubber-containing substrates compared to plants grown in the standard control. As the proportion of either grade of rubber increased, root and shoot fresh weights, height, and number of axillary shoots decreased. Flowering in geranium was delayed and the number of inflorescences reduced as the proportion of the 0.10-grade rubber increased. Plants grown in the 0.25-grade rubber failed to flower by the termination of the experiment. Poinsettia plants grown in rubber-containing substrates had reduced shoot fresh weight, height, number of bracts, and bract area compared to plants grown in the standard control. As the proportion of either grade of rubber increased, height, shoot fresh weight, number of bracts, and bract area decreased. Number of axillary branches was reduced in substrates containing 50% and 75% of the 0.10-grade rubber. Days to anthesis was unaffected by substrate.

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Michael R. Evans and Richard L. Harkess

Geranium (Pelargonium ×hortorum L.H. Bailey) `Freckles' and poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) `Freedom' were grown in six peat and shredded-rubber substrates formulated to contain 75:25:0, 50:50:0, 25:75:0, 75:0:25, 50:0:50, 25:0:75 sphagnum peat: fine-grade rubber: coarse-grade rubber (by volume). Additionally, plants were grown in a 50 peat: 30 perlite: 20 loam (by volume) control substrate. Shredded rubber-containing substrates had higher bulk densities, lower total pore space, and higher total solids than the control substrate. Fine rubber-containing substrates had lower air-filled pore space (AFP) and lower water-holding capacities (WHC) than the control substrate. Substrates containing 25% coarse rubber had lower AFP and WHC than the control, but substrates containing 50% and 75% coarse shredded rubber had higher AFP and lower WHC than the control. Shredded rubber-containing substrates had significantly higher levels of Zn than the control substrate. Plants grown in rubber-containing substrates had tissue Zn levels significantly higher than the control and at levels reported to be phytotoxic in other species. Geraniums grown in rubber-containing substrates had lower root and shoot fresh mass, were shorter, and had fewer axillary branches than those grown in the control substrate. Poinsettia plants grown in rubber-containing substrates were shorter, had lower shoot fresh mass, fewer bracts, and lower bract area as compared to plants grown in the control substrate.

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Stephen B. Gaul, Eric D. Nelson and Michael R. Evans

Rooted cuttings of 22 different Euphorbia pulcherrima Willd. ex Klotzsch cultivars were grown in root substrate inoculated with 0, 5000,15,000, and 30,000 oospores of Pyuthium ultimum Trow per 10-cm containers. The root substrate was a mixture of 50% peat, 30% perlite, and 20% soil, adjusted to a pH 5.5. Plants were grown in a greenhouse with a temperature range of 15-32 °C, and were fertilized daily with 200 ppm N (Excel 15-5-15, Scotts Co. Marietta, Ga). After 8 weeks, roots were rated for disease incidence and root fresh and dry weights were determined. The data were analyzed using ANOVA with six blocks in a 22 × 4 factorial design, linear regression, and cluster analysis. Significant differences among the responses of the cultivars were found. The slopes of the regression equations, using the log10 of the inoculum level for the X axis, were more positive for disease incidence and more negative for fresh and dry root weights in the more susceptble cultivars. The cultivars were separated, by the cluster analysis, into three groups, less susceptible, moderately susceptible, and highly susceptible. Cultivars Marblestar and Galaxy Red were representative of less susceptible, `Pepride' and `Jolly Red' were representative of moderately susceptible, and `Snowcap' and `Success' were representative of highly susceptible cultivars.

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I-Chun Pan, Ya-Fen Lu, Pei-Jung Wen and Yen-Ming Chen

Poinsettia ( Euphorbia pulcherrima ) belongs to the spurge family (Euphorbiaceae). Its place of origin is southern Mexico to Northern Guatemala. This small deciduous tree can reach more than 3 m high and grows bright red bracts in winter ( Ecke et