Towards a diagnostic test for herbicide resistance in grasses
Aims and objectives
Black-grass (Alopecurus myosuroides Huds.) is a major problem weed in winter cereal crops in the UK. Its presence causes reduction in both crop quality and yield. Chemical control (by selective graminicides) has proved useful but the occurrence of herbicide-resistant biotypes has resulted in variable control in recent years. Although herbicide resistance in black-grass was first reported in Essex in the early 1980s, more than 750 cases, from 30 English counties, have now been reported. An important aspect of black-grass control is therefore determining whether poor control is due to resistance, so that suitable management measures can be adopted. Current tests for resistance either involve transplanting plants to a glasshouse, where herbicide spray trials are carried out, or collection of seed prior to crop harvest for plate-based growth analysis. These tests are both expensive and time-consuming. A better test would be cheap, quick and would ideally provide results before the application of post-emergent herbicides, so alternative strategies could be adopted where necessary.
This study has focused on an enzyme GST (glutathione S-transferase) that is more active in the resistant biotype Peldon. Raised activities have been demonstrated in other resistant biotypes and a correlation between GST activity and fenoxaprop resistance demonstrated. A GST polypeptide has been purified from a susceptible biotype (Herbiseed) and an additional GST polypeptide, found in Peldon only, has also been purified. Monoclonal antisera raised against the Peldon polypeptide have been used to develop an ELISA (enzyme-linked immunosorbent assay) for quick detection of GST abundance in black-grass plants. This has confirmed that resistant biotypes possess increased abundance of GST polypeptide as well as increased GST activity. This ELISA test has been used to assess plants surviving herbicide treatment and to predict field performance at sites where black-grass control has been poor. As the test is carried out on plants at 2-3 leaf stage and gives a result in 3 days, it can provide useful information prior to post-emergent herbicide application. Such a test will aid resistance diagnosis and allow resistance management strategies to be started earlier in the season. The authors are grateful to the HGCA for funding and Novartis CP UK for seeds of novel biotypes and for access to field sites of known agronomy and herbicide history.
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