Inoculating the roots of barley with beneficial bacteria can help fight off aphid pests, University of Liverpool research suggests.
The work, led by Dr Sharon Zytynska, saw barley treated with Acidovorax radicis or Bacillus subtilis, which can both effectively colonise plant roots.
Initially, the team carried out controlled pot experiments, finding that the root treatments suppressed populations of the English grain aphid, Sitobion avenae. Their genetic analysis showed that when aphids fed on the inoculated plants, the plants showed different defence responses to untreated controls.
During the course of this study, the team also discovered that the way in which crops are inoculated could be critical in ensuring the highest level of pest suppression. Using a natural polymer for controlled delivery of the bacteria to roots performed better than seed soaking, and the technique meant the bacteria was viable after storage at 4°C for eight months, which would likely make the approach more practical for farmers.
Following the successful aphid control in the lab, they tested the performance of the inoculated barley in the field. Again, they saw suppression of S. avenae, first in the aphid’s winged stage, then in the wingless stage. There was also an increase in barley yield from treated plots.
The activity of parasitoid wasps, an important natural enemy of aphids, also played a role in the suppression. Additional studies showed that the microbial changes both made parasitoid wasps change their behaviour to more readily select and lay their eggs inside aphids while also making the aphids themselves more susceptible to parasitism.
With clear results above ground, Zytynska’s team went on to analyse processes at the roots of the crop. They found that inoculation shapes the microbiome of the soil community — something they now will explore in further work.
“Inoculation can suppress aphid insect populations, and we see that it’s through induced plant defences,” Zytynska told an audience at the Royal Entomological Society’s Special Interest Group for Sustainable Agriculture. While changes to the root microbiome and plant chemistry appear to be crucial, “we can’t ignore more indirect benefits through increased natural enemy control,” she added.
The team’s work with sap-feeding aphids contrasts with some previous research, which largely focused on the effects of root inoculation on chewing insects like caterpillars. But the more muted results in those studies may have been the result of measuring the wrong things, Zytynska continued.
Those experiments tended to look at the size, reproductive success and lifespan of pests feeding on plants receiving bacterial root treatments, but now, a growing body of work is highlighting that pests feed less on the treated plants — a crucial factor in the success of any biological control approach.
