Components of rhizospheric bacterial communities of barley and their potential for plant growth promotion and biocontrol of Fusarium wilt of watermelon

Abstract

This work aimed to characterize antagonistic bacteria from the field-grown barley rhizosphere, and evaluate their potential for growth promotion and biocontrol of Fusarium wilt on watermelon caused by Fusarium oxysporum f. sp. Niveum (FON). Seven bacteria were isolated and screened for plant growth promoting and antagonistic traits. Based on the results of phenotypic characterization and 16S rRNA gene sequencing, the isolates were identified to be related to Bacillus methylotrophicus (DMK-1), Bacillus amyloliquefaciens subsp. plantarum (DMK-7-2), Bacillus cereus (DMK-12), Pseudomonas brassicacearum subsp. brassicacearum (DMK-2), Pseudomonas veronii (DMK-3), Paenibacillus polymyxa (DMK-8), and Ensifer adhaerens (DMK-17). All the isolates were positive for the production of indole-3-acetic acid (IAA) and ammonia (NH 3), while negative for the production of hydrogen cyanide (HCN). Six bacteria strains (except DMK-17) were able to phosphate solubilization. All the bacteria strains, except DMK-8, were able to produce iron siderophore complexes, and possessed the proteolytic activity. Greenhouse experiment indicated six strains can decrease diseased percentage caused by FON. All the isolates enhanced plant biomass, six strains increased root volume, six strains increased root system activity in greenhouse test. Inoculation of mixtures of seven plant growth promoting rhizobacteria could be more effective in plant growth promotion and biocontrol of Fusarium wilt in watermelon.

Paenibacillus polymyxa, a Jack of all trades

“…Volatiles and NRPs produced by P. polymyxa strains also contribute to the onset of induced systemic resistance (ISR) that primes the plant for subsequent pathogen infection (Du et al, 2017;Luo et al, 2018;Park et al, 2018;Jeong et al, 2019;Li and Chen, 2019). Another, often described, biocontrol mechanism of P. polymyxa is its capability to form tight biofilms around the roots of diverse hosts, defending them from interaction with pathogenic bacteria and fungi (Haggag and Timmusk, 2008;Timmusk et al, 2009;2019;Abd El Daim et al, 2015;Luo et al, 2018;Yi et al, 2019). Whereas mostly the amount of biofilm formation has been only correlated with the biocontrol level, some studies provide solid proof for their hypothesis that biocontrol by P. polymyxa is, at least partly, a result of biofilm formation.…”

“…Plant growth promotion, measured with parameters such as shoot and root lengths and biomass, has been described for canola ( Brassica napus ), kiwifruit ( Actinidia deliciosa ), pepper ( Capsicum annuum ), watermelon ( Citrullus lanatus ), rice ( Oryza sativa ), maize, potato ( Solanum tuberosum ), cucumber, tomato ( Solanum lycopersicum ), pine ( Pinus sp. ), barley, sesame ( Sesamum indicum ), Arabidopsis thaliana (thale cress) and the ornamental plants Syngonium , Aeschynanthus , Robinia and Lilium (Bent et al ., 2001; Maes and Baeyen, 2003; Erturk et al ., 2010; Phi et al ., 2010; Hahm et al ., 2012; Lamsal et al ., 2012; Anand et al ., 2013; Xu and Kim, 2014; Kwon et al ., 2016; Padda et al ., 2016; Puri et al ., 2016; Weselowski et al ., 2016; Abdallah et al ., 2019; Jeong et al ., 2019; Yang, 2019; Khan et al ., 2020). Although the physiological effects are well‐described, detailed insight into how the growth promotion happens is not always provided.…”

“…One way PGPR can support plant growth is by increasing the acquisition of nutrients, such as nitrogen, phosphate, or iron, a phenomenon designated biofertilization. Many, but not all, P. polymyxa strains contain nitrogen‐fixing genes by which they can convert atmospheric nitrogen into ammonia, a useful nitrogen source for the plant (Bent et al ., 2001; Maes and Baeyen, 2003; Erturk et al ., 2010; Phi et al ., 2010; Hahm et al ., 2012; Lamsal et al ., 2012; Anand et al ., 2013; Eastman et al ., 2014; Xu and Kim, 2014; Kwon et al ., 2016; Weselowski et al ., 2016; Xie et al ., 2016; Abdallah et al ., 2019; Jeong et al ., 2019; Yang, 2019; Khan et al ., 2020; Zhou et al ., 2020). Isotope labelling revealed that the P. polymyxa strain P2b‐2R was capable of fixing atmospheric nitrogen and providing it to his host plant, hence increasing the plant nitrogen content (Bal and Chanway, 2012a,b; Anand et al ., 2013; Padda et al ., 2016; 2017b; Puri et al ., 2016).…”

In Vitro Study of Biocontrol Potential of Rhizospheric Pseudomonas aeruginosa against Pathogenic Fungi of Saffron (Crocus sativus L.)

“…As a result, the rhizosphere of healthy plants usually contains a lot of PGPR. Yang's research indicated that seven PGPR from the field-grown barley rhizosphere could increase plant growth promotion and biocontrol of Fusarium wilt in watermelon [11].…”

“…Due to unique environment of rhizosphere soil, numerous microorganisms gather in this area, where they play a vital role in the life history of plants [7,8]. Numerous plant growth-promoting rhizobacteria (PGPR) capable of strengthening plant nutrient absorption and immunological function have been isolated from rhizosphere soil, and a number of these have been converted into microbial fertilizers with favorable results [9][10][11].…”