KARYOTYPE ANALYSIS AND OPTIMIZATION OF MITOTIC INDEX IN PICEA-MARIANA(BLACK SPRUCE) PREPARATIONS FROM SEEDLING ROOT-TIPS AND EMBRYOGENIC CULTURES

The effect of hydroxyurea and colchicine solutions on mitotic index wa s investigated in embryogenic suspensions and in seedling root tips of Picea mariana. Hydroxyurea treatment and 0.6 per cent colchicine solu tion significantly increased the quantity of mitotic cells which were mostly in the metaphase stage. The highest mitotic index was observed in cells of embryogenic suspensions. The embryogenic lines were cytolo gically stable and their utilization for karyotype studies and techniq ue development holds great potential. The arm ratios and relative chro mosome length values showed the same trends between embryogenic cultur es and seedling root tips and among the five black spruce populations studied. This study shows that the black spruce karyotype is asymmetri c and semi-advanced, as in Larix and Abies. Three pairs of chromosomes are of the sm-type with submedian centromeres. One pair is median-sub median (msm), six pairs are m-type having median centromeres and two p airs are metacentric or M-type.