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.