Cytogenetic studies on natural hybrids between ryegrass and meadow fescue

Summary

• 1. Sixty-five plants of the natural intergeneric hybridFestuca loliacea Curt. from ten different populations were studied for morphology. Of the 55 analysed for chromosome number 24 were diploids and the rest triploids.

• 2. Seven diploid and eight triploid plants were investigated for chromosome behaviour in meiosis from the microsporocytes. Chromosome associations at pachytene, M I and ana I revealed cytologically detectable structural differences involving inversions, duplications, deficiencies and translocations in the parental genomes. Two triploids were asynaptic. Abnormal chromosome segregation, lagging of univalents, bivalents and trivalents, precocious division of the laggards, formation of chromatin bridges and fragments were observed at ana I. A high percentage of the microspores at tetrad stage had micronuclei; degeneration of microspores was seen to occur soon after this stage.

• 3. Pollen fertility for the diploids ranged from 0 to 11.9 per cent and that for the triploids less than 1 per cent to 27.9 per cent. In the triploid with two interchanges, it was the highest, being 93.3 per cent. Seed set was obtained only on open-pollination with the ryegrass parent. The back-cross plants included aneuploids with 2n=19, 20, 22 and 25 chromosomes, along with 2n=14 and 21 types.

• 4. It is concluded that the chromosomal structural rearrangements have played an important role in the origin and divergence of the basic genomes of the two parental species.