Embryogenesis and genetic stability in long term megagametophyte-derived cultures of larch

Embryogenic cultures derived from megagametophytes of Larix decidua were maintained for up to 17 years. A few lines were divided into sub-lines, which were maintained in the same manner as the others. Embryogenic tissue was grown on 1/2 strength LM medium supplemented with glutamine and casein hydrolysate at constant temperature and light regimes. Chromosome counts were conducted at various times. DNA content was assessed by flow cytometry. Embryogenesis was monitored with each transfer and records of all appearances of green mature embryos were kept. Chromosome number was found to vary. DNA content and chromosome number, both of which had doubled a number of years after initiation, stabilized around 24 chromosomes for most cultures. A few lines showed substantial increases in chromosome number. One of these lines lost vigour and died. Another line showed a further doubling of DNA content. No lines were embryogenic over the entire period. Embryogenicity was lost completely in some lines, but in others the loss was temporary, as periodic restoration of embryogenesis was observed.