Abstract
The effects of microorganisms on plant-insect interactions have usually been underestimated. While plant growth-promoting rhizobacteria (PGPR) are known to induce plant defenses, endosymbiotic bacteria hosted by herbivorous insects are often beneficial to the host. Here, we aimed to assess whether PGPR-induced defenses in broad bean plants impact the pea aphid, depending on its genotype and the presence of endosymbionts. We estimated aphid reproduction, quantified defense- and growth-related phytohormones by GC-MS, and measured different plant growth and physiology parameters, after PGPR treatment. In addition, we recorded the feeding behavior of aphids by electropenetrography. We found that the PGPR treatment of broad bean plants reduced the reproduction of one of the pea aphid clones. We highlighted a phenomenon of PGPR-induced plant defense priming, but no noticeable plant growth promotion. The main changes in aphid probing behavior were related to salivation events into phloem sieve elements. We suggest that the endosymbiont Hamiltonella defensa played a key role in plant-insect interactions, possibly helping aphids to counteract plant-induced resistance and allowing them to develop normally on PGPR-treated plants. Our results imply that plant- and aphid-associated microorganisms add greater complexity to the outcomes of aphid-plant interactions.
Highlights
First defined by Hiltner in 1904, the rhizosphere is “the soil compartment influenced by the root”, rich in microbial activity [1]
We highlighted the phenomenon of plant growth-promoting rhizobacteria (PGPR)-induced plant defense priming
Bacillus amyloliquefaciens induced an induced systemic resistance (ISR) in broad beans, because the highest contents of Jasmonic acid (JA) were measured in aphid-colonized plants [9]
Summary
First defined by Hiltner in 1904, the rhizosphere is “the soil compartment influenced by the root”, rich in microbial activity [1]. The so-called rhizobacteria interact with each other and with the plant [2]. Rhizobacteria that exert beneficial effects on plant development are called plant growth-promoting rhizobacteria (PGPR) [3]. An “operational group Bacillus amyloliquefaciens” was proposed to include the soil-borne B. amyloliquefaciens and the plant-associated Bacillus siamensis and Bacillus velezensis [7]. This group of PGPR, hereafter termed “B. amyloliquefaciens”, has a direct effect on plant growth, improving the nutritional status of plants and modulating the production of phytohormones [8]
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