The Christmas Flower II

During the middle 1950s, poinsettia breeding programs were initiated at several institutions, including the Pennsylvania State University, the University of Maryland, the USDA Research Center at Beltsville, Maryland, and by a number of commercial horticulture firms including Azalealand in Lincoln, Nebraska; Paul Ecke Ranch in Encinitas, California (Fig. 4); Mikkelsen’s in Ashtabula, Ohio; Earl J. Small of Pinnellas Park, Florida; Yoder Brothers in Barberton, Ohio; Zieger Brothers in Hamburg, Germany; and Thormod Hegg & Son in Reistad, Norway. Dr. Robert N. Stewart, of the Agricultural Research Service of Beltsville, Maryland, used his genetic training to segregate desirable characteristics such as stiff stems, larger bracts, new colors, and lasting qualities. He contributed much in determining the character of mutation forms in poinsettias, and his cooperative efforts have been extremely helpful to the commercial hybridizers.

Fig. 4. Field production of poinsettia stock plants in Southern California in the mid-1930s (click image for larger view).

With the introduction of the cultivar Paul Mikkelsen in 1963 (Fig. 5), poinsettias entered a new era. This cultivar, with stiff stems and foliage retention characteristics, provided the trade with the first longer-lasting cultivar of commercial importance. Annette Heggä Red was introduced in Norway in 1964. This cultivar was quickly followed by a number of sports. The Hegg cultivars introduced an entirely new type of multi-flowered plant to the trade because of their ability to produce from five to eight blooms from a pinch, and because of their ease of production.

Fig. 5. Paul Mikkelsen poinsettia (click image for larger view).

Fig. 6. Winter Rose the first cultivar with incurved bracts and foliage (click image for larger view).

In 1988 Eckespoint® Lilo was introduced. This was the of the first dark leaf poinsettia cultivars that were early flowering, recovered quickly after unsleeving, and had excellent foliage retention for the consumer. This cultivar required certain cultural techniques to insure good branching. In 1992, Eckespoint® Freedom™ was introduced. Eckespoint® Freedom™ contained the best characteristics of Eckespoint® Lilo while branching more consistently for the producers. Today there are over 100 poinsettia cultivars grown commercially, with one cultivar, Eckespoint® Freedom™ representing over 50% of the red market worldwide and 70-75% of that market consisting of poinsettias with red bracts. One final revolution to poinsettia cultivars was the introduction of Eckespoint® Winter Rose™ Dark Red in 1998 (Fig. 6). This cultivar was the first introduction in the “curly” family with dark red incurved bracts and deep dark green incurved foliage. (Adapted from Ecke, et al., 1990. The Poinsettia Manual [20].)


Today, poinsettias may be found in many different colors (Fig. 7) as well as product forms from mini poinsettias to large specimen trees and every size in between. Testifying to its success and popularity, the poinsettia is not only the most popular holiday flower, it is the number one flowering potted plant in the United States, with over 65 million plants sold nationwide in 2000 (61).

Fig. 7. Plum Pudding, the first poinsettia with purple bracts (click image for larger view).

Diseases

Several diseases affect production of poinsettia, including foliar diseases such as Botrytis gray mold, powdery mildew, Alternaria blight, Xanthomonas blight, Erwinia blight, Phytophthora blight, and root diseases such as Pythium, Phytophthora and Rhizoctonia root rot. Powdery mildew is a fairly recent disease problem in poinsettia production that can develop explosively late in the crop production cycle. Scab caused by Sphaceloma poinsettiae, normally a disease problem only in states like Florida and Hawaii with subtropical climates, has been introduced nationwide the past couple of seasons with infected rooted cuttings from propagators in Central America. On the other hand, black root rot caused by Thielaviopsis basicola, a soilborne pathogen, was a serious disease of poinsettia in the 1950s and early 60s until the floriculture industry moved to soilless potting mixes. Since the 1920s poinsettias in the industry have exhibited a free-branching morphotype so that cultivars develop multiple branches from a single pinch resulting in many blooms. Recently, a phytoplasma etiology was described that explained the free branching habit (47,48).

Foliar Diseases

Gray mold. Botrytis cinerea (teleomorph Botryotinia fuckeliana (de Bary) Whetz.) can cause brown spots to form on poinsettia flower bracts (Fig. 8) and leaves. The bract damage is easily confused with bract burn (Fig. 9) caused by calcium deficiency, an imbalance among potassium, calcium, and magnesium or by an ammonium-calcium antagonism. The fungus readily invades tissue damaged in any way, including that caused by bract burn. After the true flowers have fully developed, Botrytis attacks and covers them with the typical smoky, gray spores. Poinsettias are particularly susceptible to gray mold late in the season when it can cause significant damage to the aesthetic quality of plants. Gray mold development also occurs during crop shipment if infections have occurred in the production greenhouse. Large, light brown to tan, slightly sunken cankers (Fig. 10) form when older stems are invaded through wounds on large branches or through cracked branch crotches. Defoliation and death of branches occur above cankers that girdle stems.

	Fig. 8. Brown spots on poinsettia bracts caused by Botrytis (click image for larger view).		Fig. 9. Bract burn due to calcium deficiency (click image for larger view).

Fig. 10. Stem cankers caused by Botrytis infection (click image for larger view).