Detecting herbicide resistance

Weed resistance to herbicide is a critical – and growing – problem for farmers of all types all over the globe.

It is no exaggeration to say that with some weeds, in some locations in the world, resistance has already reached alarming levels, and worsens by the hour. Over 25 weed species in Australia, for example, now have populations resistant to at least one herbicide ‘mode of action’ (MOA) group. In August, it was announced that there is ryegrass in Australia that is resistant to both glyphosate and paraquat herbicides.

Herbicide resistance is the inherited ability of an individual plant to survive a herbicide application that kills others of the same species. Often, resistant weeds can survive a herbicide application at rates that are much greater than the recommended rate. The over-riding factor in the creation of herbicide resistance is the repeated application of a specific MOA herbicide group.

Waterhemp is a weed affecting field crop farmers in North America and beyond that is showing alarming levels of resistance, to seven MOA. It’s a weed species that can cause yield losses upwards of 70% in corn. It is good news, then, that new genetic mapping advances have been announced for waterhemp at the University of Illinois, US. Identifying the genes involved in resistance is a crucial step in overcoming it.

In addition, it is exciting that researchers based in Singapore and the US have designed low-cost, real-time sensors, expected to transform the screening process for herbicide resistance when the technology is commercialized.

Sensor details

The sensors, which are known as ‘CoPhMoRe’ nanosensors, have been used for other purposes in the past (to detect arsenic for example) and have now been successfully used to detect two synthetic auxin plant hormones in real time, one a plant growth regulator and one a herbicide.

One of the hormones is NAA (1-naphthalene acetic acid), a hormone applied extensively to achieve goals such as the prevention of premature flowering and fruit dropping. The other is 2,4-D (2,4-dichlorophenoxyacetic acid), a common herbicide that has been used for many years around the world. Several types of weeds found in the US and beyond are resistant to 2,4-D.

This nanosensor detection method eliminates the existing methods of checking for herbicide resistance, which involve extensive extraction, purification and analysis. Existing methods also take a long time, because identifying which weeds are resistant (and therefore need to be analyzed) requires time for weed growth.

The scientists who created the sensors are from the Disruptive & Sustainable Technologies for Agricultural Precision (DiSTAP) Interdisciplinary Research of the Singapore-MIT Alliance for Research and Technology. They worked with local collaborators from Temasek Life Sciences Laboratory (TLL) and Nanyang Technological University.

The SMART research team has already successfully tested both sensors on a number of everyday crops including pak choi, spinach and rice across various planting mediums such as soil, hydroponic and plant tissue culture.

The team’s findings are explained in a paper titled ‘Nanosensor Detection of Synthetic Auxins In Planta using Corona Phase Molecular Recognition‘.

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Broader outlook

The 2,4-D nanosensor’s ability to detect resistance or susceptibility to this herbicide, is expected to be a game-changer in the understanding of resistance.

DiSTAP principal investigator Dr Rajani Sarojam explains in a press release that this ability “could be incredibly beneficial in revealing the mechanism behind how 2,4-D works within plants and why crops develop herbicide resistance.”