AMPHIDIPLOID INDUCTION FROM DIPLOID ROSE INTERSPECIFIC HYBRIDS

A high priority in rose (Rosa spp.) breeding research is the transfer of disease resistance, especially to black spot (Diplocarpon rosae Lib .), from wild diploid Rosa species to modern rose cultivars. To this e nd, amphidiploids (2n=4x=28) were induced with colchicine from fi ce i nterspecific diploid (2n=2x=14) hybrids involving the black spot resis tant diploid species R. wichuraiana Crep, R. roxburghii Thratt., R. ba nksiae Ait., R. rugosa rubra Hart., and R. setigera Michaux. Two appli cation procedures (agitation of excised nodes in colchicine solution o r tissue culture of shoots on medium with colchicine), five colchicine concentrations (0.0, 1.25, 2.50, 3.76, and 5.01 mmol), and five durat ions (2,3,5,8, and 10 d) were used. After colchicine treatment, the ma terials were cultured in vitro and the surviving explants were examine d for the ''gigas'' characteristics typical of doubled diploids. Chrom osome counts of morphologically suspect genotypes confirmed 15 amphidi ploids among 1109 plants that survived colchicine treatment. Although the effect of colchicine treatment varied some among interspecific hyb rids, 2.50 mmol for 48 h of node agitation or 1.25 mmol for at least 5 d of shoot culture were optimal.