Chromosome characteristics and behavior differences in Allium fistulosum L., A. cepa L, their F1 hybrid, and selected backcross progeny.

Mitotic and meiotic studies were performed on Allium fistulosum, A. cepa, their F1 hybrid, and ten selected backcross (BC)1 plants [(A. fistulosum x A. cepa) x (A. cepa)]. Each BC1 plant had at least one A. cepa isozyme allele (Pgi, Idh, or Adh). Chromosome morphology and behavior differed among plants. Meiocytes were observed with one, two, or three bridges and/ or fragments, indicating at least three paracentric inversions between A. fistulosum and A. cepa. Unusual crossing over and multivalent associations suggest that the 5F subtelocentric chromosome of A. fistulosum is involved in at least one translocation. The number of bridges and fragments and multivalent associations varied between the F1 hybrid and BC1 progenies. The F1 hybrid and all BC1 progenies were either sterile or had very little seed set. Fertility was not restored in any of the selected BC1 plants.