Reproductive Characteristics of Hexaploid Alfalfa Derived From 3x ✕ 6x Crosses1
- S. E. Smith,
- R. P. Murphy and
- D. R. Viands2
Fertility and cytology were studied in hexaploid alfalfa (Medicago spp., 2n=6x=48) derived from 3x ✕ 6x crosses. The 3x and 6x parents originated from Medicago saliva ssp. sativa L. (4x), M. sativa ssp. caerulea Schmalh. (2x) and M.falcata L, (2x). A higher percentage of hexaploid plants was produced in 3x ✕ 6x crosses where the 6x parent was derived from a presumably spontaneous hexaploid than in those crosses where the 6x parent was produced by colchicine treatment. AH hexaploids derived from 3x ✕ 6x crosses were less fertile than tetraploid checks, but modest improvements in fertility were observed after two cycles of recurrent selection for hexaploidy. However, selection for hexaploidy had no significant effect on chromosomal stability. Hexaploid plants had a higher percentage of pollen mother cells (PMC) with laggards and more laggards within those PMC's than did tetraploids. When laggard frequencies were standardized relative to ploidy, no difference was observed between 6x and 4x materials for the mean number of laggards present in those PMC's having laggards. Hexaploid meiotic irregularity was positively associated with low fertility. The possibility was discussed that low levels of heterozygosity may be associated with meiotic irregularity and reduced fertility in the hexaploids studied.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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