The chromosomal locations in wheat of genes conferring differential response to the wild oat herbicide, difenzoquat

Abstract

SummaryF2, monosomic analysis involving crosses between the monosomic series of a resistant wheat variety, Chinese Spring, and a susceptible variety, Sicco, has located a major gene locus, designated Dfql, on chromosome 2B of wheat which determines the differential response of these varieties to treatment with the wild oat herbicide, difenzoquat. The allele from Chinese Spring conferring resistance is dominant and studies of the responses of Chinese Spring single chromosome substitution lines and nullisomic–tetrasomic lines for chromosome 2B indicate that this allele actively promotes resistance to the herbicide. It is suggested that this gene may prevent inhibition of DNA synthesis in the apical meristem, which is the site of action of the herbicide (Pallett & Caseley, 1980).Other chromosomes were also implicated as carrying ‘modifier genes’ which affect the ratio of resistant: susceptible plants in F2 monosomic families, namely 1D, 2D, 3A, 3B, 5B and 5D. These chromosomes may affect the retention and translocation of the herbicide to the target site and hence the threshold of response.The simple inheritance of difenzoquat resistance indicates that it should be easy by conventional breeding techniques to transfer the resistance into susceptible varieties.

Why the evolution of resistance to anthropogenic toxins normally involves major gene changes: the limits to natural selection

“…However, for one class of adaptations, the development of resistance to toxic substances of anthropogenic origin, the evidence is that major gene evolution is overwhelmingly more common than polygenic inheritance. Resistance to insecticides (Wood, 1981), warfarin in rats, mice and humans (Greaves et al, 1976;Wallace & MacSwiney, 1976;O'Reilly et al, 1964) and industrial melanism in insects (Lees,198 1) have almost always shown major gene inheritance, and it is probable that heavy metal tolerance and herbicide resistance in plants is similarly inherited (Macnair, 1989;Snape et al, 1987;Jacobs et al, 1987). Mallet (1989) in discussing the evolution of insecticide resistance, remarked on how standard neoDarwinian theory would predict that adaptation should occur by the spread of many genes of small effect, and contrasted this prediction with the observed facts.…”

Herbicide response polymorphism in wild populations of emmer wheat

“…The resistant response of the species to difenzoquat was surprising in view of the fact that the cultivated tetraploids appear almost uniformly susceptible and the cultivated hexaploids are polymorphic. Presumably this resistance is due to the DfqI gene, previously identified on chromosome 2B (Snape et a!., 1987). This suggests that the 'wild type' state is of resistance and that susceptibility has developed during cultivation.…”

“…Difenzoquat [1,2-dimethyl-3,5-diphenylpyrazolium] is used to control wild oat species in wheat, barley and rye. Again, differential responses are exhibited within bread wheat and have been shown to be controlled by variation at a major gene locus on chromosome 2B (Snape et al, 1987). However, varieties of durum wheat appear to be almost uniformly susceptible to this herbicide and only one resistant variety has been found among a sample of world varieties (Leckie, 1989 The experiments were sown either in the autumn or late winter and sprayed with the appropriate herbicide in late spring when the majority of plants had reached the 4-5 leaf stage, and when weather conditions were appropriate.…”

“…This result is surprising in view of the almost uniform susceptibility previously observed in tests of cultivated durum wheat varieties (Leckie, 1989). It appears, therefore, that this wild species may be monomorphic for the resistance allele at the locus for response to difenzoquat located on chromosome 2B (Snape et a!., 1987). These results may imply that the allele for susceptibility to difenzoquat arose subsequently to the cultivation of tetraploid wheats and during the evolution or cultivation of bread wheats, that is during the last 9000-10,000 years (Zohary & Hopf, 1988).…”

The location and effects of genes modifying the response of wheat to the herbicide difenzoquat

“…The work of Snape et al (1987) established the presence of a major gene on chromosome 2B determining the difference in the responses of Sicco and Chinese Spring, with the resistance allele from Chinese Spring being dominant. It was also established that the allele from Chinese Spring actively promotes resistance, that is, susceptibility is due to the lack of the resistance allele.…”