USE OF PROTOPLAST, CELL, AND SHOOT TIP CULTURE IN AN ELM GERMPLASM IMPROVEMENT PROGRAM

Abstract

An elm germplasm improvement program was established using three distinct approaches: (1) development of protoplast regeneration protocols with the goal of attempting somatic hybridization between Ulmus americana and disease resistant hybrids; (2) evaluation of the extent of somaclonal variation in plants regenerated from protoplasts; and (3) selection in vitro of variants from Ulmus americana callus lines exposed to toxin and culture filtrates of Ceratocystis ulmi. Plants were regenerated from protoplasts of the Dutch elm disease resistant hybrid Ulmus x 'Pioneer', but repeated attempts to regenerate Ulmus x 'Homestead' failed. Somaclonal variation has been described in a population of plants regenerated from 'Pioneer' elm protoplasts and this variation can be fixed in clones through asexual propagation. Ulmus americana selections with field level resistance to Dutch elm disease demonstrate resistance in vitro, as evidenced by callus growth on media containing culture filtrates of Ceratocystis ulmi. Attempts to select variants of previously susceptible Ulmus americana clones have been frustrated by the inability to regenerate plants from callus of adult phase Ulmus americana.