INITIATION OF SOMATIC EMBRYOGENESIS IN WHITE SPRUCE (PICEA-GLAUCA) - GENETIC-CONTROL, CULTURE TREATMENT EFFECTS, AND IMPLICATIONS FOR TREE BREEDING

The degree of genetic control and the effects of cultural treatments o n somatic embryogenesis (SE) in white spruce were investigated with ma terial derived from six-parent diallel crosses, including reciprocals. Thirty zygotic embryos from both immature and mature cones of each fa mily were cultured in media with either 2,4-D or Picloram immediately after the collection of cones and after 2 months of cold storage. Ther e were significant differences in SE initiation between immature and m ature explants, and fresh and cold-stored seeds, but there was no sign ificant differences with culture media effect. Significant variances d ue to families and to family x treatment interactions were found. The mean percentage of explants that initiated SE in each family ranged fr om 3.3% to 54.6%, with an overall average of 30.5%. The partitioning o f family variance revealed that 21.7% was due to general combining abi lity effects, 3.5% was due to maternal effects, and 5.5% was due to re ciprocal effects, but that the specific combining ability (SCA) was ne gligible. Variance due to interactions of family x treatments collecti vely accounted for 32.6%, while the remaining 37.8% of variation was a ccounted for by random error. However, when comparing the responses ob tained with the treatment combinations, the SE response for freshly ex cised immature embryo explants showed comparatively large SCA variance , whereas the SCA variance was very small in the other treatment combi nations.