Microbe-induced plant resistance against insect pests depends on timing of inoculation, but is consistent across climatic conditions

To cope with abiotic and biotic stressors, plants have developed
mutualistic associations with beneficial soil microbes, but little is
known about how extreme abiotic conditions impact microbe-induce
resistance to insect herbivores. Extreme temperatures are often
accompanied by extremes in plant water availability, which together reduce
plant growth and change plant physiology. There are potential consequences
for increasing plant susceptibility to biotic stresses, and this poses a
real challenge for plant productivity. We evaluated how the effects of
beneficial soil bacteria (Acidovorax radicis N35e) on barley plant growth
and resultant resistance against aphid infestation (Sitobion avenae) were
impacted by a single heatwave event across a plant water availability
gradient. We also tested if timing of bacterial inoculation (before or
after the temperature treatment) affected bacteria-plant interactions on
aphids. We found that heatwaves affected plant biomass allocation from
aboveground to belowground tissues. Inoculation with A. radicis led to
reduction of aphid numbers, but depended on timing of inoculation, and led
to stronger resistance when inoculations occurred closer to aphid
infestation. Remarkably, microbe-induced resistance against aphids was
consistent across heatwave and water availability treatments. This study
provides evidence that beneficial plant-bacteria interactions may
represent a potential solution for sustainable agricultural practices to
enhance plant growth and response to insect pests under climate change.
Future field trials should investigate the consistency of beneficial
effects reported here for a better understanding of multispecies
interactions in the context of global change.