Enemies at play: Interactions between a fungal pathogen and an insect pest on wheat

23rd Mar 2015

Scientists from the University of Nottingham and Rothamsted Research, which receives strategic funding from the BBSRC, have found that exposure of wheat to both a fungal pathogen and an insect pest allows the fungal disease to thrive. The research, published in the journal of Applied and Environmental Microbiology, investigated the interactions between the grain aphid, Sitobion avenae (insect pest), and Fusarium graminearum (a fungal pathogen that causes Fusarium head blight disease) on wheat.

In a controlled environment, wheat was infested with aphids and inoculated with F. graminearum, together or separately, and disease progress was monitored using visual assessment and quantification of pathogen DNA and mycotoxin accumulation (mycotoxin is the toxic substance produced by the pathogen). Wheat exposed to both the insect pest and the fungal pathogen showed a two-fold increase in disease severity and a five-fold increase in mycotoxin accumulation compared to wheat which was only infected with the fungal pathogen. The longer the aphid pest infested the host wheat prior to pathogen infection the greater the build-up of DNA of F. graminearum.

Conversely, the reproductive rate and survival of the aphid pest on infected wheat was substantially reduced. Presence of the pathogen is detrimental to aphid fitness, while aphid infestation likely breaks down the defences of wheat against the pathogen. Thus, interactions between F. graminearum and grain aphids on wheat benefit the fungal pathogen at the expense of the insect pest.

Dr Toby Bruce from the Department of Biological Chemistry & Crop Protection, Rothamsted Research, said: “In a real field situation both disease and aphids often occur together which is why we need to know how they affect each other. Our current results indicate that Fusarium head blight spreads about twice as fast when aphids are on the wheat plants. However, the relationship doesn’t benefit both partners and the aphids actually do worse on diseased plants”. These findings have important consequences for Fusarium head blight management because they suggest that fields with aphid infestation are at a higher risk”.

Dr Rumiana Ray from the Division of Plant and Crop Sciences at the University of Nottingham said:“Fusarium head blight is a significant disease on all cereals causing yield, quality and safety losses for growers worldwide. The disease can be particularly severe when it is caused by F. graminearum which is considered the most aggressive FHB pathogen and a very potent mycotoxin producer. Our results indicate that aphids play an important role in disease epidemiology by facilitating the secondary spread of the pathogen, leading to more severe disease and greater mycotoxin accumulation. We need to better understand the host responses to the simultaneous attack by the pest and the pathogen and to determine the consequences of these pest/pathogen interactions in field so that we can devise improved strategies against FHB disease and mycotoxin contamination”.

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