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Australian Herbicide Resistance Initiative (AHRI)

Proof of Concept

Fluridone Seeds

What has pure research ever done for us?

In 1974, physicist John O’Sullivan developed a mathematical tool to detect black holes. He didn’t find the black holes, but nearly twenty years later while working at CSIRO in Australia, he used this research to develop Wi-Fi. CSIRO went on to receive royalty payments of hundreds of millions of dollars for this unexpected consequence of early, pure research.

AHRI researcher Dr Danica Goggin works at the pure research level and she has also made an unexpected discovery. Danica was using an aquatic herbicide, Fluridone, to break dormancy and stimulate ryegrass germination. This is not new, however, she found that it also killed the ryegrass. Further research revealed that Fluridone stimulated germination in eight weed species including wild radish and brome grass. Fluridone was not tolerated by wheat, canola, common beans or chickpeas, but lupins and field peas grew normally.

We must keep in mind that this is pure research and is still at the laboratory proof of concept stage. It may not be as big as Wi-Fi, however pure research to evaluate an aquatic herbicide in a field situation to stimulate a 90% weed germination and then kill nearly 100% of the weeds is a classic example of where investment in pure research is necessary.

Once in a while unexpected things happen with potentially exciting consequences.

What is fluridone and how does it break dormancy?

To say that Danica Goggin is understated about her excellent research is an understatement! It’s our job to ‘talk up’ her research to ensure that the messages are heard. It was her observations in the laboratory that led to the discovery that fluridone may have a place in Australian agriculture.

Danica was using fluridone to break the dormancy of annual ryegrass, as many seed researchers have done in the past. However, Danica noticed that the ryegrass that germinated was bleached which led her to explore the herbicidal properties of fluridone.

1264_fluridone_seeds_resized

Figure 1.Fluridone treated annual ryegrass displaying signs of bleaching.

Weed germination on agar

Under controlled conditions, germinating weed seeds on agar, fluridone increased germination from a control level of 10 to 40% to over 90% for a range of weed species.

Bar chart of germination at 42% by crop species

Figure 2.Effect of Fluridone (-F & +F) on seed germination (%) under controlled conditions on agar for a range of weed species 42 days after imbibition.

Annual ryegrass germination on various soil types

Fluridone is tightly bound to organic matter which would make it less available in soils with high organic matter. Fluridone had a greater stimulation of germination on river sand or sandy loam than potting mix.

1266_Figure_2_germination_by_soil_type

Figure 3.Effect of Fluridone (-F & +F) on the cumulative germination (%) of annual ryegrass for fluridone treated potting mix (A), River sand (B) or Sandy loam (C).

Herbicidal activity

Fluridone killed nearly 100% of ryegrass seedlings on low organic matter soils. Lower ryegrass seedling mortality was observed for Fluridone treated potting mix. Fluridone appears to have herbicidal activity on many grass species of weed as well as a few dicot species, however, this is an anecdotal observation at this stage and is yet to be confirmed with detailed research.

1267_Figure_3_shoot_dry_mass

Figure 4.Herbicidal effect of Fluridone as demonstrated by annual ryegrass seedling biomass (g) for Fluridone (-F & +F) treated potting mix, River sand or sandy loam soil.

Crop tolerance

Fluridone was not tolerated by wheat, Canola, Chickpea or Common bean. However, lupin and field pea tolerated Fluridone with 100% seedling survival. Some patchy bleaching of the cotyledons of lupin and field pea was observed. These plants recovered from this phyto-toxicity and went on to grow normally.

1268_Figure_4_plant_survival

Figure 5.Survival of crop plants sown into Fluridone treated sandy loam soil.

Field testing

The efficacy of Fluridone under field conditions could not be assessed owing to the lack of rainfall at the field trial site in April 2013.

Richard Devlin from Living Farm has conducted some pro-bono trial work this year with Fluridone. The results of this research are not yet available; however it is encouraging to hear that Richard observed the herbicidal effect of Fluridone in the field. More on this later in the year.

How does Fluridone break dormancy in weed seeds?

Seed dormancy has been studied by scientists for decades, yet there are still many aspects that are poorly understood. In fact, a recent scientific paper on the issue was titled “Germination – still a mystery”. Here is a summary of what we do understand, in very simple terms

  1. Abscisic acid (ABA) is known as the dormancy hormone. Its role in dormancy is not fully understood. We know that the amount of ABA in a seed is definitely an important part of seed dormancy
  2. ABA is produced as a product of Carotenoid production.
  3. Carotenoids are like sunscreen. They protect the plant chlorophyll from the sun. Without sunscreen the plant gets burnt or bleached.
  4. Fluridone, and other PDS inhibiting herbicides, stop sunscreen (carotenoid) production. PDS is an important enzyme in carotenoid production. Group F herbicides inhibit the PDS enzyme. No PDS enzyme = no carotenoid production = bleached plants.
  5. No carotenoid production = noABAproduction = no dormancy.

ABA_synth

Figure 6.Diagram depicting the synthesis of carotenoids and their importance as ‘sunscreen’ to protect plant chloroplasts from being bleached by excess sunlight. ABA (Abscisic acid) is synthesized by the breaking of the carotenoid carbon chain into smaller pieces and one of these is oxidised into ABA.

ABA synth plus herbicide

Figure 7.Diagram showing how a PDS inhibiting herbicide such as Fluridone (Group F) stops carotenoid production leading to excess sunlight bleaching the Chloroplast resulting in plant mortality. The inhibition of carotenoid production also stops ABA production which in turn removes seed dormancy.

When a seed first matures on the parent plant it has high ABA levels. This ABA level can slowly degrade through time until a point where the ABA levels are very low and the seed is no longer dormant.

When a seed in the soil first imbibes moisture, the seed fires up new ABA production. This ABA is produced and degrades, is produced and degrades, and so on until the hormonal balance in the seed finally tips towards germination. Adding Fluridone to the seed as it imbibes moisture for the first time stops ABA production in its tracks and allows the seed to germinate immediately.

Future possibilities

One of the current limitations of using Fluridone as a herbicide is how tightly it is bound to organic matter. It may be possible to adjust the formulation of Fluridone to make it more effective in soil.

This early research showed that lupin and field pea demonstrated some tolerance to Fluridone. Future research could focus on finding more crops that are tolerant to Fluridone.

Summary

It is very early days in the investigation of the use of Fluridone as a germination stimulant and herbicide, and it is possible that Fluridone will never be registered as a soil applied herbicide in its own right. However, sharing the results of pure research such as this may just be enough to inspire activity to develop something new for weed control. It is an understatement to say that we desperately need it!

 

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