Chromosome Stability and Fertility of a Nitrous Oxide‐Derived Tetraploid Population of Red Clover¹

Abstract

The first and sixth generations of a randomly mated, autotetraploid red clover (Trifolium pratense L.) population (2n=28) derived by treatment with nitrous oxide were examined to determine changes in male and female fertility. Characters measured were chromosome pairing, pollen stainability, and seed set. Approximately equal numbers of aneuplolds (2n−1, 2n+1, 2n+2) were observed in each generation tested. These aneuploids produced less stainable pollen and seed than did euploids in greenhouse crosses, but under field cage conditions, only 2n=27 genotypes produced fewer seeds per head than the euploid genotypes (2n=28). However, clones with 27, 28, and 30 chromosomes produced lighter weight seeds than clones with 29 chromosomes. It was concluded that six generations of random mating were ineffective in changing meiotic configurations, pollen stainability, and seed yield. Although not directly compared in this study, aneuploids appeared to be produced in about the same frequency in nitrous‐oxide and colchicine‐derived tetraploid populations. Aneuploids apparently are not a major factor in the low seed yields of tetraploid red clover. It is suggested that direct selection for high seed yield may be more effective than selection for absence of aneuploids.

Sexual polyploidization in red clover

“…Pollen fertility was also not improved, as percentages of sterile grains were still high from the second to the last generation analyzed. Similar results were found by Giri et al (1983) in somatic tetraploids of red clover; percentage of aneuploids was similar and high even after six generations, what led the authors to suggest that selection for seed production may be more efficient than selection against aneuploids.…”

Nitrous oxide (N2O) induces 2n gametes in sterile F1 hybrids between Oriental × Asiatic lily (Lilium) hybrids and leads to intergenomic recombination

“…A notable advantage of using a gas for treatment is that the toxic effects, if any, can be mitigated by simply removing the tissue from the gas chamber, a process that can not be accomplished when tissues are treated with solutions. For the purpose of somatic chromosome doubling, N 2 O has been successfully applied in some plant species such as Crepis capillaries; Phalaris canariensis (Östergren, 1954, 1957) Melanrium (Nygren, 1955); wheat and barley (Tsunewaki, 1962;Dvorak et al, 1973); clover (Giri et al, 1983) and Psathyrostachys juncea (Berdahi and Barker, 1991). In many of these cases, in addition to inducing polyploids, N 2 O treatment also led to aneuploid production.…”