DIPLOIDIZATION IN MEGAGAMETOPHYTE-DERIVED CULTURES OF THE GYMNOSPERM LARIX-DECIDUA

Tested haploid embryogenic lines (n=12) of Larix dedicua Mill. initiat ed from megagametophyte tissue were maintained on half-strength LM med ium without growth regulators, The cultures were analyzed for ploidy l evel after 1-9 years. All lines tested were found to have doubled (2n= 24) their chromosome number at the end of the experiment, though there were a few lines that still gave occasional haploid counts. Flow cyto metric data of embryogenic tissue confirmed these results. Protoplasts were stained in ethidium bromide, and cultured human leucocytes and c hicken erythrocytes were used as internal standards. Haploid megagamet ophytes from immature seeds of L. decidua and known diploid culture li nes of a related hybrid (L. x eurolepis) were also analyzed by flow cy tometry, Haploid reference material had 12.3-13.6 pg DNA per cell, whe reas formerly haploid callus lines had an average of 25.0 pg DNA per c ell. The one exception was a known, genetically unstable line of L. de cidua (34.8 pg DNA per cell). The diploid cell line of L. x eurolepis had 27.6 no DNA per cell. The results show that spontaneous diploidiza tion of megagametophyte lines is relatively rapid and that both haploi d and dihaploid lines are embryogenic in larch.