Modern wheat varieties bred to rely on fertilizers have greatly reduced the number of beneficial bacteria living on or around their root system, and reintroducing these microbes may offer a way to enhance sustainable food production.
Researchers at the UK’s Rothamsted Research have concluded that modern wheat varieties have been bred to rely on nutritional inputs to maintain yields and this is impacting soil health. The findings which have been published in the ISME Journal, also indicate that modern wheat varieties, grown with inorganic fertiliser, show ‘markedly fewer beneficial root bacteria compared to their unfertilised counterparts.’
The researchers explain that modern wheats have more complex genomes, with either four (tetraploid) or six (hexaploid) sets of chromosomes due to extensive crossing and interbreeding. Ancestral varieties have simpler genomes with just two sets of chromosomes. The team performed controlled experiments to compare plant growth-promoting rhizobacteria (PGPR) associated with the diploid, tetraploid and hexaploidy wheats grown in both fertilised and unfertilised soil.
The team found that fertiliser application reduced the abundance of PGPR in polyploid wheats by 45%, making their levels no higher than in unplanted soil. This reduction was not observed in diploid wild wheats, the ancestors of modern varieties. Further analysis showed that the reduced PGPR in polyploid wheats was largely driven by a reduced selection of beneficial bacteria in modern wheats, especially from the phylum Bacteroidota.
“Our study is unique in that we test the interaction of fertiliser application and plant genotype (ploidy level) and its impact on microbiome structure and function. We found beneficial Bacteroidota to primarily associate with the roots of fertilised diploid genotypes,” said Dr Tim Mauchline, a plant and soil microbiologist at Rothamsted.
Dr Tessa Reid, the study’s lead researcher, added: "Modern wheat varieties have been bred to thrive in high-input systems. This appears to have greatly reduced the number of beneficial bacteria living on or around their root system. If we were to move to lower input systems, we will need to work out how to boost the abundance of beneficial soil microbes, so that they provide the nutritional benefits currently delivered by inorganic fertilisers."
The outcomes from the Rothamsted study could help to shape future plant breeding programmes. "Plant-microbiome interactions must be factored into future breeding to enable the development of more sustainable wheat production systems which are less reliant on high levels of fertiliser input. To date this has not been the case," said Mauchline.
While the research focused on wheat, Mauchline added that Rothamsted’s experimental approach could be applied to other crops. "The experimental approaches we have taken can certainly be applied to other crops. It is difficult to say if the findings can be extrapolated to other crops, as not all crops are polyploid. However, there is previous literature that has demonstrated differences in the root microbiome structure of domesticated and wild crops, and this has been linked to the phylum Bacteroidota being more pronounced in wild species."
The team said that further research could involve carrying out ‘microbiome transplants,’ whereby beneficial root microbes that have been reduced through domestication, will be added to modern wheat varieties. Another strategy could be to reintroduce key genetic traits to modern wheat, from their ancestors, to boost colonisation of beneficial microbiota.
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