Calendula officinalis—A Great Source of Plant Growth Promoting Endophytic Bacteria (PGPEB) and Biological Control Agents (BCA)

Abstract

The application of beneficial bacteria may present an alternative approach to chemical plant protection and fertilization products as they enhance growth and resistance to biotic and abiotic stresses. Plant growth-promoting bacteria are found in the rhizosphere, epiphytically or endophytically (Plant Growth Promoting Endophytic Bacteria, PGPEB). In the present study, 36 out of 119 isolated endophytic bacterial strains from roots, leaves and flowers of the pharmaceutical plant Calendula officinalis were further identified and classified into Bacillus, Pseudomonas, Pantoea, Stenotrophomonas and Rhizobium genera. Selected endophytes were evaluated depending on positive reaction to different plant growth promoting (PGP) traits, motility, survival rate and inhibition of phytopathogenic fungi in vitro and ex vivo (tomato fruit). Bacteria were further assessed for their plant growth effect on Arabidopsis thaliana seedlings and on seed bio-primed tomato plantlets, in vitro. Our results indicated that many bacterial endophytes increased seed germination, promoted plant growth and changed root structure by increasing lateral root density and length and root hair formation. The most promising antagonistic PGPEB strains (Cal.r.29, Cal.l.30, Cal.f.4, Cal.l.11, Cal.f.2.1, Cal.r.19 and Cal.r.11) are indicated as effective biological control agents (BCA) against Botrytis cinerea on detached tomato fruits. Results underlie the utility of beneficial endophytic bacteria for sustainable and efficient crop production and disease control.

Compatible Consortium of Endophytic Bacillus halotolerans Strains Cal.l.30 and Cal.f.4 Promotes Plant Growth and Induces Systemic Resistance against Botrytis cinerea

“…Both B. halotolerans Cal.l.30 and B. halotolerans Cal.f.4 are natural endophytes isolated from Calendula officinalis , as recently described by Tsalgatidou et al, 2023 [ 16 ]. Routinely, both strains were inoculated in 5 mL liquid nutrient broth (NB) medium and incubated overnight with shaking on an orbital platform (200 rpm) at 30 °C.…”

“…Bacterial strains Cal.l.30 and Cal.f.4 were studied for their in planta compatibility by the root colonization of A. thaliana seedlings and the plant growth effect, as mono- and co-cultures. A. thaliana seeds were surface sterilized and grown on solid half-strength Murashige and Skoog (½ MS) medium (Duchefa Biochemie, Haarlem, The Netherlands) supplemented with 0.5% ( w / v ) sucrose and 0.8% ( w / v ) bacteriological agar (Sigma, Burlington, MA, USA) as previously described by Tsalgatidou et al, 2023 [ 16 ], until further use.…”

“…The growth effect on A. thaliana morphological characteristics was determined after bacterial mono- (Cal.l.30 and Cal.f.4) and co-culture (Cal.l.30 + Cal.f.4) inoculation at 3 cm distance from root tips, as previously described by Tsalgatidou et al, 2023 [ 16 ]. Both bacterial strains, each containing ~10 8 CFU/mL (OD 600 = 0.5), were equally combined, creating a 1:1 mixture, and an aliquot of 10 μL cell suspension was inoculated.…”

“…The aim of this study was to combine the novel endophytic B. halotolerans strains Cal.l.30 and Cal.f.4, two promising biological control agents, and evaluate their plant growth-promoting and plant protection abilities as mono- and co-cultures. Cal.l.30 and Cal.f.4 were selected ahead of other isolates due to their ability to combine direct plant growth effect and strong antimicrobial activity against several plant pathogens with the secretion of novel secondary metabolites [ 16 , 17 ]. Strains were tested for their compatibility under in vitro conditions and their co-colonization capacity on A. thaliana roots.…”

The seed microbiomes of staple food crops

“…Of most importance, seed‐borne endophytes can regulate overall plant fitness through versatile plant growth‐promoting traits, such as nitrogen fixation, producing phytohormones, secretion of siderophores and enzymes and alleviating plant stress responses (Tsalgatidou et al, 2023 ). Some seed endophytic bacteria, such as Bacillus spp., Lysinibacillus spp.…”