Nematode RNAi nemesis

C&I Issue 6, 2019

Parasitic nematode worms infect almost all cultivated crops, inflicting roughly a 20% loss in annual yields. Now, scientists have discovered metabolites in soil bacteria that protect crops against nematodes.

Researchers in the Ukraine, and at the University of Sussex, investigated the use of biostimulants from metabolites of soil Streptomycetes to protect wheat against the cereal cyst nematode Heterodera avenae (Frontiers in Plant Science, doi: 10.3389/fpls.2019.00483). They found that the biostimulants boosted plant growth and development, and provided resistance against the nematode.

University of Sussex mathematician Konstantin Blyuss modelled the interaction between the bacterial metabolites, crop plants and nematodes and says that the metabolites or biostimulants work in two ways. ‘They target the nematode, turning off essential genes. In parallel, they also switch off some plant genes that facilitate entry of the nematode.’

The cereal cyst nematode CCN is a patch problem in UK cereals. ‘Pressure is probably increasing, mainly due to poor crop rotations where growers are not rotating crops in a field every season,’ explains Andy Evans, an agricultural pest scientist at Scotland’s Rural College in Edinburgh. Pesticide inputs kept nematode numbers in check, but most soil applied pesticides such as organophosphates are now withdrawn, and nematode populations are rising. ‘For some plant pathogenic nematode species in soil we have seen a 300% increase in populations over the last 15-20 years,’ says Evans.

Lab investigations revealed that the biostimulants, obtained from Streptomycetes, churned out interference RNA that complemented messenger RNA (mRNA) from plants and their nematode foes. By binding to the strands of plant or pest mRNA, this complementary RNAi causes them to be degraded, stopping the mRNA passing on instructions to make a protein, by so-called ‘gene silencing’.

Plants react to nematodes feeding on their roots by sending resources to root defence rather than investing in shoot and leaf growth, consequently plants become stunted with lower yields or uneven crop maturity. ‘There is huge potential for this strategy, but it needs to demonstrate efficacy in the field, and demonstrate no ‘trade-off’ in the crop such as reduced yields or crop quality,’ Evans explains. ‘They also need to figure out how best to apply this “technology”.’

How this RNAi technology will be regulated is another issue, he adds, questioning whether the approval process for chemical and biological pesticides will be appropriate.

Gene silencing is triggered when the biostimulants are applied to seeds.

Agro firm Bioinvest-Agro in Kiev is now producing products and selling them to small farming companies and large agribusinesses. ‘They have already been successfully used to grow wheat, rapeseed, soya, sunflower, corn as well as certain vegetables, such as cucumbers, tomatoes and peppers,’ according to Blyuss.

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