CYTOTAXONOMIC STUDIES IN HOLCUS

Abstract

With Plate 3 and 6 figures in the text) SUMMARY Studies have been made of the relative frequency and distribution in parts of Britain of the chromosome races oi Holcus mollis {zn = 28, 35, 42, 49). These show that the pentaploid is the most common race and that the distribution of the races as a whole is a reflection of varying degrees of adaptability to moisture content of the soil.Chromosome studies at meiosis and mitosis show that the tetraploid is an allopolyploid and that the hexaploid is derived from it. The pentaploid appears to be derived from a hybrid of H. lanatus {zn =14) and H. mollis {2n = 28).The hybrid nature of the pentaploid is confirmed by the discovery of natural triploid hybrids (2« = 21) from which it is presumed to have been derived by backcrossing to the tetraploid parent.With the exception of the tetraploid, the races of H. mollis reproduce almost exclusively by vegetative means. The tetraploid is fertile but is also likely to reproduce mainly by rhizomes.The success of the pentaploid is attributed to its hybrid vigour in both growth and adaptability to soil moisture. In addition its spread is favoured by the fact that its tetraploid parent does not offer much seed competition in the colonization of new areas. There is no competition from the H. lanatus parent which has different ecological requirements.It is considered feasible that the vigorous pentaploid could eventually supersede the other races of H. mollis.

The cytology of Caltha palustris: Cytogenetic relationships

“…Nor is this the only fertile and successful uneven polyploid. Pentaploid (2n = 35) and particularly heptaploid (2n = 49) Holcus mollis are fertile (Jones, 1958). Successful crosses involving the pentaploid Agrostis stolonjfera (2n = 35) with two TABLE 8 Chromosome pairing at meiosis in the 2n= 56 tace of Caitha palustris L.…”

Population biology of intraspecific polyploidy in grasses

“…Over its range, D. glomerata has a very wide variety of cytotypes, genotypes and phenotypes, occurring as single or multiple cytotype populations (Lumaret 1988b;Lumaret & Barrientos, 1990). The diploid:tetraploid:pentaploid complex of Holcus mollis X H. lanatus likewise has regional differences superimposed on the local populations that contain varying combinations of cytotypes (Jones, 1958;Richard et al, 1995). Others that have not been as intensely studied are likely to be very complex as well, e.g.…”

“…Other important points in the population ecology of intraspecific polyploidy are illustrated in Holeus (Jones, 1958;Richard et al, 1995), Anthoxanthum (Hedberg, 1967), Daetylis (Lumaret 1988b), and Panieum (Hultquist et al, 1996(Hultquist et al, , 1997, where in all cases there are inconsistencies in the breeding relationships and behaviour of cytotypes (such as hybridization range. This is understandable given the recurrent formation of auto-and allopolyploids, and backcrossing within the complex.…”

“…However, in a surprising number of species, some individuals with odd-numbered ploidy levels, e.g. pentaploids in Holcus mollis (Jones, 1958;Jones & Carroll, 1962), triploids in Dactylis glomerata (Zohary & Nur, 1959;Borrill, 1978), enneaploids (9x) in Andropogon gerardii (Norrmann et aI., 1997) have good fertility, linking the ploidy series into an evolutionary whole (Jackson, 1976;Lumaret, 1988a;Thompson & Lumaret, 1992).…”

“…Cytotypes of selected members Sutherland, 1986Myers, 1947Myers, 1947Myers, 1947Myers, 1947Hickman, 1993Sutherland, 1986Jones, 1958Richard et al, 1995von Bothmer & Jacobsen, 1986KankanpiUi et aI, 1996 Myers, 1947Myers, 1947Myers, 1947Sutherland, 1986Myers, 1947Sutherland, 1986Myers, 1947Myers, 1947Myers, 1947Myers, 1947Hickman, 1993Sutherland, 1947Myers, 1947Myers, 1947Sutherland, 1988Myers, 1947Sutherland, 1986Burton, 1942Myers, 1947;Quarin et al, 1982 Burton, 1942Myers, 1947Myers, 1947Myers, 1947Myers, 1947Myers, 1947Myers, 1947Sutherland, 1986…”