Advanced “double binding” properties which research has confirmed lead to clear benefits against disease have been revealed for new fungicide IZM (isopyrazam) as UK approval is sought to extend its use into wheat.

Paul Varney: In developing IZM, scientists were able to build advanced properties into its chemical structure

IZM, from Syngenta, is already used successfully in barley in the broad-spectrum fungicide Bontima (isopyrazam + cyprodinil), launched in spring 2010.

Now, Syngenta is seeking to obtain UK approval for IZM in a different fungicide for disease control in wheat. Approval is hoped for in time for use during 2011.

“IZM is a next-generation member of the much-heralded SDHI group of fungicides and works by shutting down fungal energy production,” says company cereal fungicide expert Paul Varney. “However the significant thing with IZM is that it is from a specific ‘benz-pyrazole’ branch of SDHI chemistry.

“Within this, in developing IZM, our scientists were able to build advanced properties into the structure of the molecule, with the breakthrough coming because IZM essentially consists of two parts. A ‘pyrazole’ part binds it to the target site in the fungus, while the other part, containing the ‘benz’ element, is attracted to waxes and lipids.

“It is this benz-pyrazole structure which gives IZM its advanced double binding properties whereby it not only binds strongly to the fungus – making it highly potent against disease – but also to the leaf wax – where it provides long-lasting and durable protection.

“We knew from early evaluations that the product looked special, now research has added to this. Field trials in wheat have shown excellent control of the major diseases of Septoria tritici and yellow and brown rusts, extended green leaf retention and repeatedly high yield responses,” he confirms.

According to Syngenta fungicide biochemist Dr Andy Corran, IZM works in the energy production ‘factories’ within fungal cells, the mitochondria, to block the activity of the critically-important enzyme succinate dehydrogenase (SDH). Hence succinate dehydrogenase inhibitors, or SDHIs.

“The key thing about IZM is that it binds very tightly into this target site,” stresses Dr Corran, “fitting a bit like a hand in a glove.

“Laboratory testing comparing SDHI chemistry has shown that a very low concentration of IZM was needed to have an inhibitory effect on the mitochondria of Septoria.

“This partly explains its high potency, but also the SDH enzyme is located in a membrane, and membranes are very rich in lipids. Because of the lipid-loving nature of the other part of the IZM molecule, the belief is that it has a high affinity for this part of the fungal cell, so is able to concentrate there. You could think of it as sort of seeking out its target,” he adds.

Turning to the second double binding aspect of IZM, binding to leaf wax, Syngenta head of biokinetics David Bartlett says research has shown that most of the IZM applied to a leaf remains tightly bound into the surface, where it forms a stable, protective barrier against disease attack.

“The combination of the lipid-loving part of the molecule which is highly attracted to the leaf wax, plus good stability to ultraviolet light, and the relatively slow breakdown of IZM, all contribute to its long-lasting protection,” he explains. “Importantly, IZM also shows good resistance to wash-off by water.

“Interestingly, although most IZM does remain on the surface, some of it is still able to enter the leaf. From here it can pass to the opposite surface, and we have shown that it is also able to redistribute systemically inside the leaf in the plant’s water stream to control disease remote from the point of application. In this way it can help protect areas where spray droplets may not reach.”

According to Paul Varney, the development of benz-pyrazole chemistry is an exciting prospect for wheat. “Because IZM belongs to the benz-pyrazole chemical group it is also active against strobilurin and triazole-resistant strains of disease. Overall it has shown broad-spectrum activity against a range of diseases, potent activity and long-lasting control.”

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