Abstract
Since the discovery that entomopathogenic fungi can live inside plants as endophytes, researchers have been trying to understand how this affects mainly plants and herbivores. We studied how inoculation of Vicia faba L. (Fabales: Fabaceae) plants with Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Ascomycota: Hypocreales) (strain GHA) either via the seeds or leaves influenced the nymph production of two successive generations of Aphis fabae Scopoli (Hemiptera: Aphididae). While we did not find any difference in nymph production for the first generation of aphids, second-generation aphids on both seed- and spray inoculated plants produced significantly higher numbers of nymphs than aphids on uninoculated plants. This emphasizes the importance of two (or multi-) generational experimentation. Beauveria bassiana was recovered from 26.0, 68.8 and 6.3% of respectively seed-, spray inoculated and control plants, thus, demonstrating its ability to live as an endophyte in V. faba. The confirmation that plants inoculated with entomopathogenic fungi can have a positive effect on pest insects makes careful consideration of these multi-trophic interactions imperative.
Highlights
Today we know that plants associate with a wide array of mutualistic symbiotic microorganisms, which play a vital role for plants, as they act as the first line of defense against invading pathogens [1], provide nutrients [2], and protect plants from abiotic stress [3, 4]
Results of endophytic B. bassiana having a negative effect on herbivores rarely focus on more than one generation [21], and as insect immunity is influenced by successive exposures to the same pathogen, observing longer-term effects on pest insects, when possible, is important [22, 23]
It is for instance well documented that sub-lethal doses of pesticides can stimulate aphid reproduction [24, 25] and that the effect can be enhanced in transgenerational experimentation [26]
Summary
Today we know that plants associate with a wide array of mutualistic symbiotic microorganisms, which play a vital role for plants, as they act as the first line of defense against invading pathogens [1], provide nutrients [2], and protect plants from abiotic stress [3, 4]. One group among these microbes, the entomopathogenic fungi, has previously escaped the attention of scientists. Discovered roles of entomopathogenic fungi include endophytism [5, 7], plant disease antagonism [8], plant growth promotion, and rhizosphere colonization [9, 10].
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