Herbicide resistance case study blackgrass Alopecurus myosuroides Huds

Black-grass is an autumn-germinating annual grass that is a major weed of winter cereal crops in many countries (Figure 12.7). Its presence can result in yield reductions of up to

Figure 12.7 Black-grass in a field of wheat. On the left side the field is free of black-grass. On the right the black-grass population is approximately 500 plants m-2. Yield will be seriously reduced in the part of this trial where black-grass has been allowed to remain (photograph courtesy of J.P.H. Reade).

Figure 12.7 Black-grass in a field of wheat. On the left side the field is free of black-grass. On the right the black-grass population is approximately 500 plants m-2. Yield will be seriously reduced in the part of this trial where black-grass has been allowed to remain (photograph courtesy of J.P.H. Reade).

44% (Moss 1987) and in some cases results in total crop loss. Black-grass is capable of producing a very high number of seeds that remain viable in the soil for up to seven years. In the early 1980s poor herbicidal control of black-grass was reported at a farm in Peldon, Essex, UK where the PS II-inhibiting herbicide chlorotoluron (CTU) was routinely used for weed control. Subsequent studies demonstrated that the Peldon biotype was resistant to CTU (Moss and Cussans, 1985). Little or no reduction in photosynthetic rate was noted when field-rate CTU (3,500 g a.i. ha-1) was applied to the Peldon biotype in vivo (Sharples et al., 1997; Figure 12.8).

Since the early 1980s many further cases of herbicide resistance to different herbicides have been reported in black-grass. By 1999, as many as 750 herbicide-resistant populations had been identified in the UK alone (Moss et al., 1999). Herbicide resistance in black-grass has also been reported in Belgium, France, Germany, Israel, The Netherlands, Spain, Switzerland and Turkey (Heap, 2009). Many of these cases involve cross- or multiple resistance, and in the UK herbicide resistance due to enhanced metabolism is considered endemic.

A number of studies have attempted to identify the mechanisms responsible for herbicide resistance in black-grass. GST activity in the herbicide-resistant biotype Peldon is approximately double that in herbicide-susceptible biotypes (Reade et al., 1997). Study of further biotypes demonstrating resistance to fenoxaprop-ethyl and clodinafop-propargyl showed correlation between the level of herbicide resistance and level of GST activity (Reade et al., 1997). GST activities were found to be raised in a number of black-grass biotypes that had previously been characterised as possessing enhanced metabolism resistance, but not in biotypes that had been characterised as possessing target site resistance or that were herbicide susceptible (Cocker et al., 1999 ; Reade and Cobb, 2002). Field studies have further demonstrated that subpopulations of black-grass that have survived herbicide treatment have higher GST activity and abundance than the untreated 'parent' populations (Reade et al., 1999 ; Figure 12.9), which implies that the individuals with lower GST activity and abundance have been removed by the herbicide treatment. Studies

Susceptible

Resistant

-WA^VWj

Resistant

2 110

I 100

u 90

o 80

0 5 10 15 20 25 30 35 40 45 50 55 Chlorotoluron (kg a.i. ha-1)

Figure 12.8 (a) CO2 uptake of susceptible (o, •) and resistant (- ■) black-grass over a 24-h time period. Plants were initially treated with distilled water (•, ■) or chlorotoluron added at the amount recommended in the field (3.5 kg a.i. ha-1; o, □). A dark period is indicated by the shaded area on the x-axis. (b) The effect of increasing amounts of chlorotoluron (kg a.i. ha-1) on the fresh weight of susceptible (•) and resistant (□) black-grass, 2 weeks after herbicide treatment. The calculated doses to cause a 50% reduction in fresh weight were 0.93 and 39.3 kg ha-1, respectively, giving a resistance factor of 42. Reproduced from Sharples et al. (1997, with permission from the Annals of Botany and Oxford University Press).

0 5 10 15 20 25 30 35 40 45 50 55 Chlorotoluron (kg a.i. ha-1)

Figure 12.8 (a) CO2 uptake of susceptible (o, •) and resistant (- ■) black-grass over a 24-h time period. Plants were initially treated with distilled water (•, ■) or chlorotoluron added at the amount recommended in the field (3.5 kg a.i. ha-1; o, □). A dark period is indicated by the shaded area on the x-axis. (b) The effect of increasing amounts of chlorotoluron (kg a.i. ha-1) on the fresh weight of susceptible (•) and resistant (□) black-grass, 2 weeks after herbicide treatment. The calculated doses to cause a 50% reduction in fresh weight were 0.93 and 39.3 kg ha-1, respectively, giving a resistance factor of 42. Reproduced from Sharples et al. (1997, with permission from the Annals of Botany and Oxford University Press).

suggest that the increased GST activity in resistant biotypes is not due solely to increased abundance of a GST present in both susceptible and resistant plants, but is also due, in part, to the presence of a GST not detected in susceptible biotypes. Cummins et al. (1997) identified GSTs with molecular weights of 27kDa and 28kDa in addition to a 25-kDa GST in resistant biotypes: the susceptible biotype only had the 25-kDa GST. Reade and Cobb (1999) purified a 30-kDa GST from resistant black-grass that was absent from susceptible black-grass. This GST, the identity of which was confirmed by polypeptide sequencing (Reade and Cobb, 2002), showed different kinetic properties to the one found in both susceptible and resistant biotypes.

CTU did not induce GST activity in either biotype (Sharples et al., 1995) but treatment with the herbicide safeners benoxcor, flurazole and oxabetrinil did increase GST activity

All plots, prior to treatment

Untreated

All plots, prior to treatment

Untreated

ELISA response

ELISA response

ELISA response

Fenoxaprop-ethyl

ELISA response

Clodinafop-propargyl

Fenoxaprop-ethyl

Clodinafop-propargyl

<D 6-

<D 3-

1

<D 2 Fr 0

<D 1 -Fr 0

r

ELISA response

Isoproturon

ELISA response

ELISA response

Isoproturon

ELISA response

c 4e

CT 2-e1

ELISA response

Figure 12.9 GST abundance in the field, measured by ELISA using monoclonal anti-A myosuroides GST antiserum. (a) Prior to herbicide treatment; (b-e) 25 days after treatment. Arrow indicates plants giving a low ELISA response (b) that are absent from treated plots (c,d,e). (Reproduced from Reade and Cobb, 2002.)

in susceptible but not in resistant biotypes (Sharpies, 1996). This is interesting, as studies in wheat (Triticum aestivum L.) have indicated that some herbicide safeners do increase glutathione conjugation of herbicides (Tal et al., 1993, 1995; Edwards and Cole, 1996). GST activity in black-grass increases from winter to spring, which corresponds to a drop in the efficacy of the herbicides fenoxaprop-ethyl and clodinafop-propargyl with respect to black-grass control (Milner et al., 1999, 2001).

Cytochrome P450s have also been implicated in herbicide resistance in black-grass. Kemp and Caseley (1987) and Kemp et al. (1988) used the P450 inhibitor 1-aminoben-zotriazole to demonstrate that P450s played a role in metabolism of both chlortoluron and isoproturon in a resistant black-grass biotype. Hall et al. (1995) also showed that inhibitors of P450 activity reduced tolerance to chlortoluron and reduced herbicide metabolism in a resistant black-grass biotype, although this was not the case for fenoxaprop (Hall et al. 1997). Cell culture studies by Menendez and De Prado (1997) also suggest a role for P450s in chlortoluron metabolism. It is tempting, therefore, to interpret these findings as demonstrating a role for P450s in chlortoluron metabolism, but not in fenoxaprop metabolism, in black-grass. GST activity in resistant black(grass biotypes has been identified against fenoxaprop, fluorodifen and metolachlor (Cummins et al., 1997).

Interestingly, Brazier et al. (2002) have also identified O-glucosyltransferase in a resistant black-grass biotype, raising the possibility of a third mechanism of enhanced metabolism resistance in this species.

Was this article helpful?

0 0
Detoxify the Body

Detoxify the Body

Need to Detoxify? Discover The Secrets to Detox Your Body The Quick & Easy Way at Home! Too much partying got you feeling bad about yourself? Or perhaps you want to lose weight and have tried everything under the sun?

Get My Free Ebook


Post a comment