Facilitation of Sclerotinia sclerotiorum infestation by aphid feeding behaviour is not affected by aphid resistance in oilseed rape
Description
The relationship between aphids and Sclerotinia stem rot in oilseed rape is rarely examined because they are often studied alone. We have observed a significant correlation between the number of aphids and the occurrence of Sclerotinia stem rot in our field studies. The electropenetrography (EPG) was used to evaluate the effects of Breveroryne brassicae (Linnaeus) on two oilseed rape cultivars while acquiring, vectoring, and inculcation of Sclerotinia sclerotiorum Lib. (de Bary) ascospores. The results showed that aphid feeding followed by dropping ascospore suspension significantly increased the incidence of S. sclerotiorum. Aphids were capable of adhering to ascospores and carrying them to the healthy plants, causing disease. The results of the EPG analysis indicated that aphid feeding behaviour was significantly altered in all leaf tissue levels following infection with S. sclerotiorum. Aphids initiated their first puncture significantly sooner, began probing mesophyll cells earlier, increased significantly the frequency of both brief probing and intracellular puncturing, and had a significantly shorter pathway duration. On infected aphid-susceptible cultivars, aphids secreted more saliva, but reduced ingestion compared to aphids feeding on non-infected oilseed rape. Additionally, S. sclerotiorum can directly impact aphid feeding behaviour through ascospores. Aphids carrying ascospores started to puncture cells earlier, with a significant increase in the frequency and duration of short probes and cell punctures, shortened pathway durations, increased salivation, and reduced ingestion compared to aphids not carrying ascospores. On aphid-susceptible cultivars, aphids carrying ascospores delayed the onset of puncture, but on resistant cultivars shortened the onset of puncture. It is clear that there is a mutual interaction between aphids and S. sclerotiorum. The impact of S. sclerotiorum on aphid feeding behaviour is directional, favouring the spread of the fungus, which is altered by cultivar resistance to aphids.