Pesticide Resistance Strategies and Tactics for Management (1986) / Chapter Skim
Currently Skimming:
Modes and Genetics of Herbicide Resistance in Plants
Modes and Genetics of Herbicide Resistance in Plants
Pages 54-73
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 54... ...
Warnings about the possibility of weeds evolving resistance were issued soon after the phenoxy herbicides were introduced (Abel, 1954~; however, as no confirmed cases of resistance to phenoxy herbicides occurred, the warnings were ignored even after the first triazine-resistant weeds appeared. In Europe and the United States triazine resistance has become a serious problem: at least 42 species have resistant biotypes.
|
From page 55... ...
, evolved in South Carolina, after about 10 years of tr~fluralin use as the sole herbicide in monoculture cotton. Dose response curves vary among separately evolved resistant biotypes.
|
From page 56... ...
The potential economic risk is great: while it now costs cat $12/ha to treat sensitive weeds with atrazine, if all major corn weeds become resistant the alternative treatments would cost cat $125/ha (Ammon and IrIa, 1984~. A second problem involving resistant weeds is "problem soils." Repeated applications of herbicides can create problem soils when soil-applied herbicides can no longer control susceptible weeds.
|
From page 57... ...
In our model (Gressel and Segel, 1978, 1982) the factors governing the rates of evolution of herbicide-resistant weeds, including the effects of the seed bank, are expressed in the equation: Nn = No (1 + faln~n, where Nn is the proportion of resistants in a population in the nth year of continued treatment of a herbicide, and No is the initial frequency of resistant individuals in the field before herbicide treatment.
|
From page 58... ...
would become apparent in the field only when more than 30 percent of the plants are resistant. The scale on the right indicates the increase in resistance from any unknown initial frequency of resistant weeds in the population; whereas the scale on the left starts from a theoretically expected frequency of a recessive monogene character in a diploid organism.
|
From page 59... ...
The phenoxy herbicides have a much lower selection pressure because their shorter soil persistence allows late-season weed germination. Even without this late-season germination the actual effective selection pressure of the phenoxies is lower than the triazines.
|
From page 60... ...
cP 1.5= 1.0 m .c 0.5 0 c FIGURE 3 Special properties of most evolved atrazine-resistant weeds. A: Lack of increased chlorophyll fluorescence due to treatment with atrazine.
|
From page 61... ...
An interesting development for managing resistance is the use of a tridiphane, an herbicide "extender" that inhibits GST in the Poaceae; thus, much lower levels of atrazine need to be used (Lamoureux and Rusness, 1984~. Lowering the triazine levels should decrease the rate at which dicots evolve triazine resistance (i.e., the slopes in Figure 2 would be less acute)
|
From page 62... ...
Until triazine resistance occurred the phenyl-ureas were believed to have a totally identical binding site with the triazines (Pfister and Arntzen, 1979; Arntzen et al., 1982~. Triazine-resistant biotypes, however, were found to have different cross-tolerances to the various phenyl-urea and uracil herbicides (Table 21.
|
From page 63... ...
So far all triazine-resistant weed biotypes are susceptible to diuron, even if not to other phenyl-urea herbicides, but this need not continue (Table 21. There is probably a spectrum or continuum of binding sites that can be mutated in organisms that gives varying crossspecificities of herbicides affecting photosystem II.
|
From page 64... ...
There are even cases, studied only in tissue culture, of possible gene duplications (Gressel, in press [al)
|
From page 65... ...
The selection pressure of triazine treatments enriches for triazine-resistant plants (which are almost always less fit than the wild type) and stabilized resistance in the population.
|
From page 66... ...
Adequate long-term recommendations are needed for weed control along these roadways and the new areas where resistant biotypes continually appear. The involvement of a peculiar protein in membranes of the plastics (thylakoids)
|
From page 67... ...
67 :~ .~ ca In o 4 o 4 C~ ._ Cal Pa .s o .e o ._ o IS: EM ._ Cal o · _ Cal Cal ._ Cal .s ¢ Cal [L)
|
From page 68... ...
LESSONS FROM BIOTECHNOLOGY There are compelling commercial reasons for biotechnologically conferring cost-effective herbicide resistance to crop species (Gressel, in press [a]
|
From page 69... ...
Chlorsulfuron and other sulfonyl-urea herbicide-resistant mutants are easily obtained and regenerated to resistant plants (Chaleff and Ray, 19841. Resistance in tobacco is from a single dominant gene that modifies aceto-lactate synthase, the sole enzyme target of this group.
|
From page 70... ...
1981. Rapid detection of triazine resistant weeds using chlorophyll fluorescence.
|
From page 71... ...
1984. Chloroplast-coded atrazine resistance in Solanum nigrum: psbA loci from susceptible and resistant biotypes are isogenic except for a single codon change.
|
From page 72... ...
1976. Dichloracetamide antidotes enhance thiocarbamate sulfoxide detoxification by elevating corn root glutathione content and glutathione-S-transferase activity.
|
From page 73... ...
1982. Nucleotide sequence of the gene for the M,32,000 thylakoid membrane protein from Spinacia oleracea and Nicotiana debueyi predicts a totally conserved primary translation product of M,38,950.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.