CULTURE OF OVULES CONTAINING IMMATURE EMBRYOS OF EASTERN COTTONWOOD IN VITRO I

--Hybrid ovules containing immature embryos were excised from capsules on cut branches of eastern cottonwood (Populus deltoides Bartr.). Ovules in the less than 21-days post-pollination age-class produced callus only when cultured on a modified Murashige and Skoog medium. Single shoots developed from 35% and callus developed from 39% of ovules 21 to 40-days post-pollination. Ovules in the older than 40-days post-pollination age-class produced only single shoots. Adventitious leaves formed on hypocotyls and cotyledons of some single shoots. ABBREVIATIONS perlite located in the bottom of the pot. The pot is then placed in 5 cm of water. Floral buds are BAP = 6-benzylaminopurine; ECM = embryo forced in mid or late winter. After pollination, culture medium_ MS = Murashi_e and Skoog high 4 to 16 weeks are required for eastern cottonwood mineral salts; PVP = polyvinylpyrrolidone; SPM = capsules to mature viable seed. Due to this long shoot proliferation medium, maturation period, capsule mortality can be high and some crosses produce few or no seeds (Farmer The genus Populj_sscontains some of the most 1976). For instance, at the University of productive pulpwood, lumber, and fuelwood species Illinois in 1984, 44 poplar crosses were attempted in the temperate zone. Eastern cottonwood (_. but only II produced seedlings. Mortality could deltoides Bartr.) may supply part of the predicted occur at any stage of seed maturation. increase in the need for fiber (Dickmann and Stuart 1983). In _924, a hybridization program to In order to circumvent the capsule mortality develop _ast-growing poplar hybrids for the United associated with greenhouse crossing, Kouider et Sta_es was initiated (Schreiner 1937). Subseal. (1984) developed a tissue culture system to quently other breedin_ programs have been estabrescue immature embryos of eastern cottonwood. In fished to produce improved poplar types, the genus Populus, many tissue culture systems have been investigated (Durzan and Campbell 1974, Poplar hybridization is commonly performed in Bonga and Durzan 1982). In most studies, the a greenhouse where cut branches from selected explant tissues have been apical and axillary buds trees cas be forced to flower and then crossed (Bawa and Stettler 1972, Berbee and Hildebrandt u_der controlled conditions. At the University of 1972, Chalupa 1974, Lester and Berbee 1977, Illinois. the method "du Plancon en Pots" (Joennoz Whitehead and Giles 1977, Christie 1978, Chalupa and Vallee 1972) has been used. This method con1979, and Kim etal. 1981). Other explants have sists of inserting several female branches down included cambial stem sections (Mathes 1964, through 15 cm of a rooting medium into 5 cm of Mathes and Einspahr 1965, Wolter 1968, Ahuja 1983), root-segments (Winton 1968, 1970a, 1970b), leaf sections (Bychenkova and David 1978, Wei-lun et al. 1980, Ahuja 1983), and adventitious roots IA paper presented at the Fi_tn _L_I ('Briandand Venverloo 1973, Ahuja 1983). Hardwood Forest Conference held at the University o:f lllinois, Urbana, IL on April 15-17, 1985. This research was initiated to expand and further develop an in vitro system to rescue immature 2Spaeth Fellow, Department of Forestry; embryos of eastern cottonwood. Our objectives Associate Professor of Horticulture, Department of were: (I) to determine the minimum age at which Horticulture; Associate Professor of Forest ovules containing immature embryos could be Genetics, and Associate Professor of Forestry, rescued reliably and (2) to document the in vitro Department of Forestry, University of Illinois, regeneration capacity of ovules from variou---sageUrbana,IL 61801USA. classes.