April 8, 2024
Written by: Peter Newman
Can wild radish evade HWSC?
Every time I have given a presentation about harvest weed seed control (HWSC), without fail the question has arisen, will the weeds adapt to grow prostrate or shed their seeds to avoid HWSC?
The answer is, of course, YES, it’s possible.
And the second half of the answer is there are things we can do to avoid this happening, and despite our weeds having amazing ability to adapt, HWSC has a long future.
The next two editions of AHRI insight will tackle this issue for the common Australian weed, Wild Radish.
Dr. Mike Ashworth and Dr. Gayle Somerville from AHRI have recently published several papers in this area.
In this edition we’ll take a look at some modelling of the potential for wild radish to change its flowering time with HWSC use.
Next month we’ll show you a population of wild radish that sheds its pods.
Let’s start with the modelling.
In short, past research showed that wild radish could easily shift in flowering time when selected, however, a new model produced at AHRI predicted only small shifts in flowering time under field conditions, and these flowering time shifts only accrued when herbicidal use was not fully effective.
Why?
Diversity baby!
In 2015, we reported on a study conducted by AHRI researcher Mike Ashworth who selected for different wild radish flowering times. Following just five generations of selection in the glasshouse, Mike managed to ‘breed’ wild radish that flowered after just 29 days compared to the normal 59 days. You can read about it here: https://www.ahri.uwa.edu.au/wild-radish-paradox/
Now Mike has taken this study a step further to understand the potential for wild radish in the field to change its flowering time to evade HWSC. As the control of flowering time in plants is highly complex, involving lots of genes, Mike and Gayle produced a “simplified” model that recreated the flowering time shifts in the 2015 study.
Remember that the 2015 study deliberately ‘bred’ early flowering wild radish and is an overestimate of what is likely possible in the field.
On top of this AHRI added additional factors such a gene flow, seed production etc. to the model. This was a mind-bending job! The resultant model allows AHRI to cram in 10 or 20 years of weed control use into an afternoon to see what effect management will have on resistance development.
As a result, Mike and Gayle have recently published two papers.
Paper 1 shows that while there are likely hundreds of genes involved in flowering time adaptation, AHRI researchers were able to produce a model capable of describing the reduction in flowering time observed in the glasshouse study in 2015 where early flowering wild radish was selected.
Paper 2 tests the model developed in Paper 1 using a likely field scenario. This modelling output showed that while wild radish contains the genetic diversity to adapt its flowering time, in the field it was found that flowering time shifts were far less than expected. Just 12 days. This is far less than the 29+ days found in the glasshouse.
Paper 2 also showed that flowering time shifts only occurred in the model, when the effective herbicidal kill rate was reduced. Therefore, whilst HWSC is effective, don’t be complacent and think that HWSC is here to clean up for a bad weed control job. Keep the pressure on.
The results from this model is great news for HWSC, but remember that HWSC is highly effective and there are many more ways a weed population can evade (become resistant to) HWSC. So, keep an eye on your populations and report patches that persist despite your best HWSC efforts!
So, what does this mean?
1. HWSC is a powerful weed control technique but is not likely to affect flowering time as much as we think, and
2. Diversity still matters! Shifts in flowering time only occurred when we let a lot of survivors go to seed.
Summary
In short, we feared that HWSC would create very early flowering time wild radish populations. This work shows that this risk may not be as great as we thought. Early flowering can be caused by many factors. These include drying climate including late starts to the season and early finishes favouring early flowering individuals and excellent early weed control that shortens the growing season for anything that survives. Spray topping can also select for early flowering.
As early flowering increases the risk of early seed shedding, we may need to manage maturity timings. This can be done by diversity your herbicides and crop rotations to kill weeds at different times of the year. You want to keep the weeds on their toes!! Anything that is predictable feeds resistance.
Also, and importantly, the 2015 work showed that earlier flowering wild radish populations don’t grow as big as their late flowering counterparts, so HWSC and crop competition go hand in hand.
Papers
Check out these papers here:
Posted in: AHRI Insight, Herbicide evolution and technology