Chromosome doubling and fertility study of Alstroemeria aurea x A. caryophyllaea

Self-pollinations of a diploid (2n = 2x = 16) interspecific hybrid Alstroemeria aurea x A. caryophyllaea, resulted in no seeds. Backcrosses of the hybrid with parent A. aurea did not produce any seeds. In an attempt to restore the hybrid fertility, an efficient in vitro procedure has been developed and applied effectively in the chromosome doubling of the diploid hybrid. Forty-one percent of the treated plants were proven to be truly tetraploid by chromosome counts and stomatal measurements after applying 0.2 to 0.6% colchicine for 6 to 24 hours. Over 87.5% of these colchicine-induced tetraploids were stable and retained their tetraploidy after one year of growth. The fertility of the hybrid was not restored although the pollen stainability was increased from 0 to 12% after chromosome doubling. Cytological studies on the pollen mother cells (PMCs) of the sterile diploid hybrids revealed abnormal meiotic behaviors. In addition, aneuploid chromosome numbers, ranging from 2n = 1 to 2n = 18, were observed in over 45% of the PMCs examined. PMCs of the colchicine-induced tetraploids showed that meiotic chromosome pairings were normal in most cases (1.59 sub(I) + 15.07 sub(II) + 0.05 sub(III) + 0.03 sub(IV)). These results indicate that the sterility of this hybrid is not only caused by parental chromosome differences, but other complex fertility /sterility-regulating mechanisms are involved too.