2020

AHRI researchers have show in this report that a single P450 gene in a cross-pollinated weed species L. rigidum confers resistance to herbicides of at least five modes of action across seven herbicide chemistries.

Weed risk assessment systems are used to estimate the potential weediness or invasiveness of introduced species in non-agricultural habitats. However, an equivalent system has not been developed for weed species that occur in agronomic cropland. Therefore, the Agricultural Weed Assessment Calculator (AWAC) was developed to quantify the present and potential future adverse impact of a weed species on crop production and profitability (threat analysis), thereby informing or directing research, development, and extension (RDE) investments or activities.

The aim of this study was to determine whether weed patches could be differentiated from the crop plants, based on height differences.

This study provides examples showing that target-site resistance to POST herbicides and non-target-site resistance to PRE herbicides can be overcome by offering direct evidence across many L. rigidum populations screened. Evolved resistance to binary herbicide mixtures in individual plants may require the accumulation of multiple traits (at least two genetic traits) conferring resistance to each herbicide component applied at the maximum recommended dosage.

This research reveals the complexity of the α-tubulin gene family in individuals/populations of the cross-pollinated weedy species L. rigidum, and highlights the need for better understanding of the molecular architecture of tubulin gene families for detecting resistance point mutations. Although TUA4 is a commonly expressed α-tubulin isoform containing most frequently reported resistance mutations, other mutant tubulin isoforms may also have a role in conferring dinitroaniline resistance.

Authors: Jinyi Chen, Zhizhan Chu, Heping Han, Eric Patterson, Qin Yu and Stephen Powles

Glyphosate is often tank-mixed with auxinic herbicide 2,4-D for grass and broadleaf weed control. In this paper, the authors examined the possible interaction of 2,4-D and glyphosate in barnyard grass, Echinochloa colona. The results showed that 2,4-D antagonizes glyphosate remarkably in glyphosate resistant populations but only marginally in susceptible populations. This antagonism is related to reduced glyphosate uptake and (to a lesser extent) translocation. As 2,4-D has multiple, unpredictable effects on other herbicides, care must be taken when tank-mixing herbicides with 2,4-D.

This Special Issue of Plants comprises papers that describe the current status and future outlook of herbicide resistance research and development in weedy and domestic plants, with topics covering the full spectrum from resistance mechanisms to resistance management.

This study provides evidence that trait(s) enabling efficient trifluralin metabolism in Lolium rigidum are purged from the population under prosulfocarb recurrent selection.

It is speculated that survival to prosulfocarb via a lack of metabolic herbicide activation, and survival to trifluralin conferred by enhanced herbicide metabolism, are mutually exclusive.

In this work AHRI researcher Dr. Mechelle Owen surveyed and quantified weed seed infestation of the crop seed that farmers would be planting. In Australia, farmers save their own crop seed (wheat, barley, pulse crops, non-hyrbid canola) for planting in the subsequent growing season. Farmers produce their saved crop seed on low weed burden crop fields, so as to minimise weed seed contamination. This survey was done in 2015. This is the third AHRI survey, with the first conducted in 1998 (Powles & Cawthray 1999) and a larger second survey in 2009 (Michael, Owen & Powles 2010). In this third survey in 2015, Mechelle Owen surveyed 81 crop seed samples, each of 10 kg crop seed (wheat, barley, canola, lupins).

Resistance to the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) in wild radish (Raphanus raphanistrum) appears to be due to a complex, multifaceted mechanism possibly involving enhanced constitutive plant defence and alterations in auxin signalling. Based on a previous gene expression analysis highlighting the plasma membrane as being important for 2,4-D resistance, this study aimed to identify the components of the leaf plasma membrane proteome that contribute to resistance. Key results included: two receptor-like kinases of unknown function (L-type lectin domain-containing receptor kinase IV.1-like and At1g51820-like) and the ATP-binding cassette transporter ABCB19, an auxin efflux transporter, were identified as being associated with auxinic herbicide resistance.