THE EFFECT OF ANEUPLOIDY ON KARYOTYPE ABNORMALITIES IN WHEAT PLANTS REGENERATED FROM SHORT-TERM AND LONG-TERM SOMATIC EMBRYOGENESIS

Somatic embryogenesis was initiated from immature embryo culture of Tr iticum aestivum stocks including disomic, ditelosomic and nullisomic-t etrasomic Chinese Spring wheats. Using chromosome counts of root tip c ells, tissue culture-induced variation was observed in the plants rege nerated after both short- (4 months) and long-term (14 months) culture , The analysis was performed in order to identify whether particular c hromosome arms increased or limited the frequency of chromosome number abnormalities. Short-term regenerants from the aneuploid genotypes pr oduced on average more plants (about 14%) with abnormal chromosome com plements than did the euploid Chinese Spring line (3.5%). Most of the abnormal aneuploid karyotypes proved to arise from unbalanced chromoso me number in the starting immature embryos. This also suggests that a limited range of abnormal chromosome complement did not affect regener ation, Compared with CS, ditelosomic lines such as DT 4BS, DT 6BL and DT 7DL possessed a highly significant increase in somatic chromosome n umber instability after short-term culture. The frequency of regenerat ed plants with karyotype abnormalities reached 80% after extended tiss ue culture time, in both the euploid and aneuploid lines, demonstratin g that abnormalities were induced during the in vitro culture process. After 14 months' culture, DT 1AL, DT 2AL and DT 7BL lines were more s table than CS. The experimental results suggest that regeneration thro ugh somatic embryogenesis does not ensure normality in chromosome comp lement. After long-term cultures, the regeneration capacity was unchan ged despite the fact that 80% of regenerated plants possessed abnormal chromosome complement.