Vegetative and reproductive characteristics of poinsettia altered by a graft-transmissible agent

Poinsettia (Euphorbia pulcherrima Willd. ex. Klotzsch) cultivars were divided into free-branching and restricted-branching groups. Auto and reciprocal grafts were made among three free-branching cultivars, Annette Hegg Brilliant Diamond (BD), Annette Hegg Topwhite (TW), and Annette Hegg Hot Pink (HP), and two restricted branching cultivars, Eckespoint C-1 Red (CR) and Eckespoint C-1 White (CW). When CR scions were grafted onto BD stocks, vegetative characteristics of branching pattern and leaf morphology of CR plants were altered when compared to the control graft combination CR/CR (scion/stock). Branching pattern was determined by pinching the scion above the 12th node and measuring axillary shoot length, diameter, and node number 30 days later. CR scions grafted onto BD stocks produced a plant very similar to BD plants when axillary shoot length and node number were compared. However, axillary shoot diameter and leaf morphology were intermediate between CR and BD plants. Changes were retained after two generations of serial vegetative propagation and are considered permanent. The reproductive characteristics of anthesis date, bract color, and cyathia cluster diameter were not influenced by the stock. CR/BD plants produced twice as many axillary inflorescences as BD/BD or BD/CR plants, while CR/CR plants did not produce any. All of the free-branching cultivars were able to alter the vegetative characteristics of all of the restricted-branching cultivars