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The genus Dactylis (Poaceae) in Poland in relation to its Eurasian distribution
Abstract
The genus Dactylis L. is a polyploid complex which consists of 16 diploids (2n = 14), 7 tetraploids (2n = 28) and 2 hexaploids (2n = 42), distributed mostly in Central Europe and also in Asia and North Africa. In Poland it is represented by one species Dactylis glomerata L., within which three subspecies as well as their hybrids have been distinguished: subsp. glomerata (2n = 28), subsp. aschersoniana (Graebn.) Thell. (2n = 14) and subsp. slovenica (Dom.) Dom. (In = 28).
Two diploid subspecies of Dactylis glomerata L. are recognized to be present in Italy. D. glomerata subsp. aschersoniana is present in mesic mixed broadleaved forests of Friuli (North-eastern Italy); its occurrence in other parts of the territory is questioned. D. glomerata subsp. reichenbachii is an endemic of Pinus sylvestris woods of Alto Adige. Furthermore, diploid individuals have been observed irregularly scattered through Northern Italy. Such individuals are morphologically very variable, and do not deserve a particular taxonomic treatment. Biological and evolutionary relationships within the species are discussed. An analytical key to the italian entities of Dactylis is given.
A partir d'une étude morphologique de populations de dactyle, l'auteur décrit un taxon nouveau sur le littoral atlantique.
1. A survey has been made of chromosome numbers in natural populations of Dactylis. Diploids (2n=14), tetraploids (2n=28) and hexaploids (2n=42) have been found in our material, and B-chromosomes have been noted, particularly in diploid plants. In the F.A.O. collections accession numbers are given wherever interesting chromosome numbers have been found. 2. Chromosome pairing has been studied in each of the chromosome number groups, and in diploid x diploid, and tetraploid x tetraploid hybrids. The gross similarity of the chromosome sets in Dactylis has been demonstrated. Minor genetic and (or) chromosomal differences have been found between tetraploid populations. 3. Chromosome pairing in the natural hexaploids is regular but variable. 4. Interchange heterozygotes have been observed and analysed in the three chromosome groups. 5. Chromosome breakage and reunion is frequent in plants derived from seed which has lost much of its germination capacity.
The average cross fertility is low and influenced by genotype, rather than by the taxonomic position of the parents. A few genotype combinations were reasonably fertile. On the average, crosses were more successful with the tetraploid as the female parent.
Chromosome counts on the progeny of crosses between diploid and tetraploid races ofDactylis show that tetraploid hybrids are produced as well as the expected triploids. The relative proportions of 4x and 3x hybrids vary greatly in different crosses, and the data suggest that parental geno-type influences the result. Overall, the frquencies of 3x and 4x hybrids are about equal, with no indication of a difference between the reciprocal 2x×4x and 4x×2x cross-combinations except perhaps in the case of diploids and autotetraploids of the same subspecies. Rare triploid hybrids are found in crosses between diploid subspecies ofDactylis. The mechanisms by which a diploid plant could donate two genomes to its offspring are discussed in relation to theDactylis situation, and the evolutionary significance of 4x hybrids formed in this way is considered.