The Effects of Biostimulants on Induced Plant Defense

Abstract

The search for innovative and alternative methods for chemical control to manage pests is an increasingly growing reality. The use of biostimulants such as plant growth promoting rhizobacteria (PGPR) and humic acids (HA) has been shown to improve many agronomic characteristics of plants while increasing yield. These biostimulants also alter the production of secondary metabolites with consequences for insect herbivores. Here we review the role of biostimulants such as PGPR and HA in promoting and eliciting plant defenses. The cascading effects of using these biostimulants on insect herbivores and their natural enemies are discussed in this context. Synergism between biostimulants are also discussed. The potential role of these products in augmenting agricultural productivity is highlighted as is further need for additional research. This review highlights the potential of this tool to enhance integrated pest management in agricultural production systems, reduce the use of pesticides, and increase the efficiency of fertilization while supporting healthier more pest-resistant plants.

Humic Substances in Combination With Plant Growth-Promoting Bacteria as an Alternative for Sustainable Agriculture

“…The individual use of these biostimulants in biocontrol has already been established in the literature; however, there have been few reports on the mechanisms involved in the interaction of these biostimulants on the protection of plants against pathogens (Glick, 2015;Jindo et al, 2020;Pereira et al, 2021). We hypothesize that HSs and PGPB can use different approaches to contribute to the plant's defense mechanisms, such as (1) combined application of these biostimulants is capable of altering secondary plant metabolism and pathways related to stress responses, providing the plant with greater tolerance to biotic stress.…”

“…These microorganisms also play a relevant role in biological control. PGPB induce biochemical and plant defense responses, causing induced systemic resistance (ISR; Pereira et al, 2021). In addition to synthesizing compounds that inhibit the growth of pathogens, they can also induce greater production of allelochemicals and change the composition of exudates in plants, contributing to a reduction in pest development (Bashan et al, 2014;Pankievicz et al, 2021).…”

“…The priming effect of HA in corn was generate a decrease in negative impacts of stressors on this plant (Canellas et al, 2020). The action of HSs on the protection of plants against pathogens was documented, and studies have shown that HSs can increase the plant defense system against harmful microorganisms, directly acting in the inhibition of these organisms or inducing the growth of microorganisms with antagonistic action to the pathogen, thus allowing greater protection for the plant (Jindo et al, 2020;Pereira et al, 2021).…”

Organic matter in the pest and plant disease control: a meta-analysis

“…Indirectly, the effect of HS can be associated with the effects of other organic matter sources, such as V, C and teas in the control of pests and diseases in plants, since HS are ubiquitous in all natural organic material. HS can indirectly induce the plant's defense system against harmful microorganisms by inhibition mechanisms or by promoting the growth of microorganisms antagonists of pathogens, thus allowing greater protection for plants [88]. We found in the literature one evidence highlighting the relationship between plant defense mechanism and HS.…”

“…De Hita et al [131] reported the increase of SA and JA in cucumber plants, 24 and 72 h after HA foliar application, respectively, indicating a possible effect on the activation of SA and JA signaling pathways as plant defense response. Based on the evidence found in literature, humified organic matter may be involved with RAS [17,88,119,120,131], but further studies are needed to prove it.…”