The genetics of arsenate tolerance in Yorkshire fog, Holcus lanatus L.

Abstract

The genetics of arsenate tolerance in Holcus lanatus is investigated. Three tolerant plants from an abandoned arsenic mine, and three non-tolerant plants and one less tolerant plant (C9) from an uncontaminated site were crossed. Five polycrosses between plants from F1 crosses between mine and non-tolerants were set up. Four polycrosses between tolerant F2 progeny, and four polycrosses between non-tolerant F2 progeny, were established. A polycross involving the progeny of a single tolerant plant allowed to cross at random with a normal population was also established. The results are broadly compatible with a single-gene model for tolerance, with tolerance being dominant. The majority of F2 crosses segregated in to 3:1 ratios, and backcrosses gave 1:1 ratios. The crosses between C9 and non-tolerants gave 1:1 ratios, which suggests that the less tolerant C9 was heterozygous for tolerance. All crosses between non-tolerants gave all non-tolerant offspring. In one cross a major gene for albinism also segregated, and linkage of the tolerance gene to this gene (r.f. =35%) was demonstrated. A number of families produced progeny ratios incompatible with the simple major gene model. Possible causes of these anomalous crosses are discussed and it is suggested that the tolerance gene may show variable penetrance depending on the genetic background.

Reproductive biomass in Holcus lanatus clones that differ in their phosphate uptake kinetics and mycorrhizal colonization

“…Little difference between SPU and nonSPU plants has been found in the kinetics of P uptake by the low-affinity uptake system (Meharg & Macnair, 1990). Genetic studies have shown that suppression of the P-arsenate uptake carrier in H. lanatus is inherited and under the control of a major gene, with resistance being dominant (Macnair et al, 1992 ;Meharg & Macnair, 1992a).…”

“…A difference in flowering behaviour between SPU plants from mines and uncontaminated soils may be due to physiological differences other than SPU. However, an advantage of using non-mine SPU plants is that they are not in linkage disequilibrium with other traits selected for in mine environments (Macnair et al, 1992 ;Meharg & Macnair, 1992a), so it is more likely that the differences in flowering are due to P nutrition.…”

“…For other metals, such as Cu, Pb, Zn and Cd, there is usually a very low frequency of resistant plants on ' normal ' or uncontaminated soils, and not all ' normal ' populations of these species actually possess the resistant individuals (Symeonidis et al, 1985 ;Macnair et al, 1992). Resistance to arsenate in H. lanatus is exceptional.…”

Zinc tolerance and accumulation in metallicolous and nonmetallicolous populations of Arabidopsis halleri (Brassicaceae)

“…exposure to very high level of metals in soils) (Meerts & Van Isacker, 1997). Genetic variation in the degree of tolerance in species showing ecotypic tolerance is well documented (Macnair et al, 1992 ;Schat & Ten Bookum, 1992 ;Schat et al, 1993Schat et al, , 1996Smith & Macnair, 1998). Smith & Macnair (1998) have shown that in Cu-tolerant Mimulus guttatus the variation in Cu tolerance observed among the tolerant populations was due to a variation in modifier genes and not to the major tolerance gene itself.…”

Differences in the genetic basis of leaf dissection between two populations of Crepis tectorum (Asteraceae)

“…For instance, large differences between species or conspecific populations can have a relatively simple genetic basis (Prazmo, 1965;Macnair, 1977;Gottlieb, 1984;Doebley & Stec, 1991;Macnair et a!., 1992;Orr & Coyne, 1992;Dorweiler et a!., 1993), implying that evolutionary change sometimes occurs more rapidly than would have been the case if numerous loci were involved (Fisher, 1958;Lande, 1981Lande, , 1983. The rate of fixation should be greatest for dominant mutations because of the low frequency of individuals homozygous for rare alleles in large outcrossing populations (Haldane, 1924), although there is a potential for fixation of advantageous recessive alleles in (partially) self-fertilizing taxa (Charlesworth, 1992).…”