Cytogenetic investigations in diploid and autotetraploid populations of Festuca pratensis

Cytogenetic investigations were conducted in diploid and induced autotetraploid population plants of a local Norwegian variety of Festuca pratensis, Huds. Meiotic investigation in 50 randomly selected diploid genotypes revealed that 42 % of the clones were heterozygous for paracentric inversions and 22 % for interchanges. In the autotetraploid C2-generation, 73 % of the clones had normal euploid chromosome number (2n= 28). Among the remaining aneuploid clones the chromosome number ranged from 26 to 30, 2n=27 and 2n=29 being the most common. At first metaphase quadrivalents were regularly formed, the mean number among euploid clones ranging from 1.73 to 3.33. The corresponding variation in the mean number of chiasmata was from 22.67 to 26.33. Generally, the quadrivalents disjoined regularly at first anaphase, and the major causes of aneuploid gametes were univalents and trivalents. The mean percentage of normal pollen grains and seed set was significantly higher in the eutetraploid clones than in the diploids. The aneuploid classes with 27 and 29 chromosomes had significantly lower fertility than the eutetraploid class. Between the aneuploid classes no significant difference appeared, but the figures indicate a more serious effect upon fertility of one missing than of one extra chromosome. The yielding capacity of diploids exceeded that of eutetraploids by 7 %, and the difference was highly significant. An even geater difference appeared between eutetraploids and aneupløids. Between the two aneuploid classes with 27 and 29 chromosomes, however, no significant difference could be detected.