DNA detective work is helping to better understand and map the movement of key weed species in a bid to improve management and direct future research.

Using a genotyping by sequencing approach, research has found that two of Australia’s most-prolific weeds are highly mobile, while a third weed shows more evidence of local movement.

Ryegrass and feathertop Rhodes grass populations are genetically very similar, indicating high levels of movement. In contrast, fleabane populations are genetically different, indicating that local-scale movement is more important. The University of Queensland’s Dr James Hereward and his team have been undertaking population genetic studies. The work is a key component of area-wide weed management.

"Understanding how far and how quickly a weed species can spread is important in planning an area-wide weed management program,” Dr Hereward says.

"Highly mobile weeds more rapidly become shared problems, especially as increasing numbers of weed species are becoming resistant to key herbicides such as glyphosate.”

The study investigated these weed species based on their high potential for mobility, herbicide resistance occurrence and grower concerns. It considered fleabane and annual ryegrass in the New South Wales Riverina region, fleabane in Victoria’s Sunraysia region and feathertop Rhodes grass in Queensland’s Darling Downs region.

The work was part of the GRDC-supported Area Wide Management project, which looked at cross-sector collaboration and its ability to make inroads into weed control challenges across private and public land.

Movement

Finding out more about weeds genetically helps to better understand their movement and has ramifications for resistance.

For example, the genetic data for annual ryegrass and feathertop Rhodes grass shows levels of outcrossing that point to an ability to ‘stack’ different herbicide resistance mechanisms. Outcrossing is a normal, natural occurrence where genes can be transferred to another plant of the same species.

Dr Hereward says that high levels of outcrossing can also enable a weed species to acquire resistance more rapidly to multiple herbicide modes of action. For both weeds, herbicide resistance can also be spread by the movement of pollen as well as seeds.

For fleabane, the genetic data indicated high levels of inbreeding, which is consistent with its reputation for self-pollination. However, the populations’ genotypic diversity does indicate that outcrossing occurs at very low rates.

This was a surprising result, Dr Hereward says. “We expected fleabane to be one population and highly mobile. Instead, its genetics are more driven by what was in the field the year before. We did also find evidence for long-distance dispersal of fleabane in the data.”

Ramifications

Dr Hereward says the key takeaway is that all three weeds are mobile.

"Their high mobility within these regions will lead to the rapid spread of herbicide resistance genes across the landscape. It highlights the importance of early detection and the elimination of herbicide-resistant populations.

"Coordinated efforts to control herbicide survivors and eliminate resistant populations across land uses would have area-wide community benefits by reducing the spread of herbicide resistance, especially at the regional scale.”

Area Wide Management project

The recently completed Area Wide Management project explored the potential to make inroads into the ever-evolving challenge of weed control across private and public land.  It investigated and demonstrated the agronomic, economic and social benefits of tackling the problem of mobile weeds on a cross-industry scale. Three main regions were looked at: Queensland’s Darling Downs, New South Wales’s Riverina and Victoria’s Sunraysia.

More information: James Hereward,  [email protected]; Area wide management for cropping systems weeds podcast