Rhizobacteria activates (+)‐δ‐cadinene synthase genes and induces systemic resistance in cotton against beet armyworm (Spodoptera exigua)

Abstract

Gossypol is an important allelochemical produced by the subepidermal glands of some cotton varieties and important for their ability to respond to changing biotic stress by exhibiting antibiosis against some cotton pests. Plant growth-promoting rhizobacteria (PGPR) are root-colonizing bacteria that increase plant growth and often elicit defence against plant pathogens and insect pests. Little is known about the effect of PGPR on cotton plant-insect interactions and the potential biochemical and molecular mechanisms by which PGPR enhance cotton plant defence. Here, we report that PGPR (Bacillus spp.) treated cotton plants showed significantly higher levels of gossypol compared with untreated plants. Similarly, the transcript levels of the genes (i.e. (+)-δ-cadinene synthase gene family) involved in the biosynthesis of gossypol were higher in PGPR-treated plants than in untreated plants. Furthermore, the levels of jasmonic acid, an octadecanoid-derived defence-related phytohormone and the transcript level of jasmonic acid responsive genes were higher in PGPR-treated plants than in untreated plants. Most intriguingly, Spodoptera exigua showed reduced larval feeding and development on PGPR-treated plants. These findings demonstrate that treatment of plants with rhizobacteria may induce significant biochemical and molecular changes with potential ramifications for plant-insect interactions.

The Role of Plant-Associated Microbes in Mediating Host-Plant Selection by Insect Herbivores

“…Previous research suggests PGPR-mediated reduction of cucurbitacin C, which reduced beetle feeding damage, could also decrease attraction in foraging or ovipositing beetles [56]. In contrast, another study reported that cotton plants (Gossypium hirsutum) treated with PGPR had increased levels of the defense compound gossypol and increased expression of genes that regulate its production, resulting in decreased performance of beet armyworm larvae on PGPR plants [163]. As a generalist herbivore, beet armyworm may avoid PGPR-associated cotton plants with increased gossypol that reduce its performance.…”

Bacillusspecies in soil as a natural resource for plant health and nutrition

“…and conferred ISR in loquat trees against Colletotrichum acutatum (Wang et al ). Zebelo et al () showed that Bacillus spp. conferred protection in cotton against Spodoptera exigua through higher gossypol accumulation which was again related with the activation of genes involved in JA defence signalling network.…”

Does drought stress modify the effects of plant‐growth promoting rhizobacteria on an aboveground chewing herbivore?

“…Importantly, the effect of root‐associated microbes on herbivorous insects varies from positive (D'Alessandro et al ., ; Megali et al ., ) to negative (van Oosten et al ., ; Pangesti et al ., ; Zebelo et al ., ) and to date we do not fully understand the factors responsible for this variation. Biotic factors such as feeding guild and degree of specialization of the insects have been shown to affect the outcome of plant–microbe interactions.…”