Optimizing Biocontrol Activity of Paenibacillus xylanexedens for Management of Hairy Root Disease in Tomato Grown in Hydroponic Greenhouses

Abstract

Hairy root disease (HRD) caused by rhizogenic Agrobacterium biovar 1 strains affect tomato, cucumber, eggplant, and bell pepper grown in hydroponic greenhouses and can cause considerable yield losses worldwide. Recently, Paenibacillus xylanexedens strains (ST15.15/027 and AD117) with antagonistic activity against rhizogenic agrobacteria were identified. In this study, we present results of greenhouse trials of two consecutive growing seasons (2019 and 2020) to examine the potential of these two biocontrol organisms (BCOs) under practical conditions. BCO-treatment at a 107 colony forming units (CFU)/mL density resulted in a considerable reduction of the HRD infestation rate, confirming the biocontrol potential of the two P. xylanexedens strains. Results revealed that a single BCO strain (ST15.15/027) performed equally well as the mixed inoculum of both strains. The same level of biocontrol activity was even achieved when the BCO inoculum density was reduced to 105 CFU/mL. qPCR analysis further showed that Paenibacillus was still present in rockwool substrate near the end of both trials, indicating that they persist well in a rockwool environment and that application at the start of the trial is sufficient to protect tomato plants until the end of the trial. Altogether, these results are highly valuable for further optimization and exploitation of P. xylanexedens as a biocontrol product for the control of HRD in hydroponic greenhouses.

Evaluation of sequence-based tools to gather more insight into the positioning of rhizogenic agrobacteria within the Agrobacterium tumefaciens species complex

“…Another objective in this study was to shed more insight into the taxonomy of strains causing HRD. Interestingly, while HRD was originally associated with pathogenic R. rhizogenes (former biovar 2) strains, in recent studies it was observed that on (hydroponically grown) Cucurbitaceae and Solanaceae plants the causative agent is generally Agrobacterium biovar 1 harbouring a root-inducing plasmid [5, 6, 73, 107].…”

“…The diversity of this genus is also exemplified by the diverse effects it exerts on plants, with several Agrobacterium spp. being beneficial or non-pathogenic, while other species induce severe plant diseases, such as crown gall disease or hairy roots disease (HRD) on a wide range of host plants, often resulting in a considerable decrease in yield and associated economic losses [4][5][6][7].…”

Geographically Disperse, Culturable Seed-Associated Microbiota in Forage Plants of Alfalfa (Medicago sativa L.) and Pitch Clover (Bituminaria bituminosa L.): Characterization of Beneficial Inherited Strains as Plant Stress-Tolerance Enhancers

“…Thus, the strains Bacillus cereus , Bacillus nealsonii , Priestia megaterium , Pantoea agglomerans , Enterobacter ludwigii , Stenotrophomonas maltophilia , Paenibacillus pabuli , Paenibacillus peoriae and Paenibacillus polymyxa are highly recognized as growth promoters in different plant species [ 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 ]. Others, such as Enterobacter hormaechei , Atlantibacter hermannii , Paenibacillus amylolyticus , Paenibacillus tundrae and Paenibacillus xylanexedens , have less support in the literature, but have also been reported as beneficial or characterized as potentially beneficial due to their abilities, such as phytohormone production or the solubilization/mobilization of inaccessible nutrients [ 89 , 90 , 91 , 92 , 93 , 94 ]. On the other hand, most of these strains have been defined as enhancers of plant response and tolerance to stresses such as drought ( B. cereus , P. megaterium , E. ludwigii , P. agglomerans, P. amylolyticus and S. maltophilia ), salinity ( B. nealsonii , P. agglomerans , E. ludwigii and S. maltophilia ), high/low temperature ( B. cereus , P. tundrae and P. xylanexedens ), or heavy metals ( B. nealsonii ).…”

Endophytic Paenibacillus polymyxa LMG27872 inhibits Meloidogyne incognita parasitism, promoting tomato growth through a dose-dependent effect

“…RS BABA-induced resistance has previously been described to be effective in tomato against M. incognita ( Devran and Baysal, 2018 ) and M. javanica ( Oka et al, 1999 ). Paenibacillus polymyxa displayed antimicrobial activity against many other plant pathogens, such as hairy root disease, caused by rhizogenic Agrobacterium in tomato ( Vanlommel et al, 2020 ; Vargas et al, 2021a , b , and antifungal activity in peanuts ( Arachis villosa ) ( Costa et al, 2021 ) and hemp ( Cannabis sativa ) ( Mahmoud and Jabaji, 2021 ). Other P. polymyxa varieties such as NMA1017 have shown to exert biocontrol activity against Rhizoctonia solani on maize ( Zea mays ) in vitro , while pot experiments with bean ( Phaseolus vulgaris ) exhibited the growth of fungal pathogens such as R. solani and Pythium ultimum ( Chávez-Ramírez et al, 2020 ).…”