Isolation and Screening of Extracellular PGPR from the Rhizosphere of Tomato Plants after Long-Term Reduced Tillage and Cover Crops

Abstract

Plant growth promoting rhizobacteria provide an innovative solution to address challenges in sustainable agro-ecosystems, improving plant growth as well as acting as agents of biocontrol. In this study autochthonous bacteria were isolated from the rhizosphere of processing tomato plants (Solanum lycopersicum L.) cultivated with conservation agriculture practices (i.e., reduced tillage and cover crops), and evaluated for both growth-promoting activities (PGPAs), and antagonistic potential against the phytopathogenic pest Sclerotinia sclerotiorum. Considering the several activities of PGPR, we decided to structure the screening with a hierarchic approach, starting from testing the capability of fixing nitrogen. The obtained bacteria were processed through the molecular typing technique rep-PCR (Repetitive Extragenic Palindromic) in order to discriminate microbial strains with the same profiles, and identified via 16S rDNA sequencing. Thirty-eight selected isolates were screened in vitro for different activities related to plant nutrition and plant growth regulation as well as for antifungal traits. Isolated bacteria were found to exhibit different efficiencies in indoleacetic acid production and siderophore production, phosphate solubilization and biocontrol activity against the widespread soil-borne plant pathogen S. sclerotiorum. All the 38 bacterial isolates showed at least one property tested. With a view to detect the suitable candidates to be developed as biofertilizers, the selected isolates were ranked by their potential ability to function as PGPR. Thus, consortium of native PGPR bacteria inoculants may represent a suitable solution to address the challenges in sustainable agriculture, to ensure crop yield and quality, lowering the application of chemicals input.

Integrated Genomic and Greenhouse Assessment of a Novel Plant Growth-Promoting Rhizobacterium for Tomato Plant

“…PGP rhizobacteria strain UC4115 was isolated from the rhizosphere of Solanum lycopersicum L., cultivated with conservation agriculture practices (i.e., reduced tillage and cover crops), in a commercial field situated in Gabbioneta-Binanuova (45 • 12'03.0" N; 10 • 12'27.8" E), Cremona, Po Valley (Northern Italy), following the method described by Guerrieri et al (2020). Briefly, to isolate the rhizosphere bacteria, root samples were shaken vigorously to remove not tightly adhering soil.…”

“…According to Guerrieri et al (2020), the extracted DNA was amplified with 16S rRNA, using the universal primers P1 (5 ′ -GCGGCGTGCCTAATACATGC-3 ′ ) and P6 (5 ′ -CTACGGCTACCTTGTTACGA-3 ′ ) (Di Cello and Fani, 1996). Sanger sequencing of PCR products was carried out at GATC Biotech (Ebersberg, Germany).…”

“…The PGP traits of K. variicola UC4115 and A. brasilense Sp7 were assessed following the methods described by Guerrieri et al (2020). Briefly, for qualitative estimation of tri-calcium phosphate solubilization, the strains were spot inoculated on GY/Tricalcium phosphate medium (Ambrosini and Passaglia, 2017), and incubated at 30 • C. After 7 days of incubation plates were observed for development of a clear halo zone around the colony, the halo's diameter was evaluated according to Ambrosini and Passaglia (2017).…”

“…The genus Klebsiella , is one of the common genera detected in the rhizosphere system (Podile and Kishore, 2006 ), and the species Klebsiella variicola strains have been found to naturally colonize the rhizosphere of tomato plant (Guerrieri et al, 2020 ; Sunera et al, 2020 ). In particular, the plant growth-promoting (PGP) capacity of distinct strains of K. variicola were confirmed in glasshouse experiments as well as in field trials, both in terms of yield increase and product quality improvement (Kim et al, 2017 ; Yang and Yang, 2020 ).…”

Selected Plant-Related Papers from the First Joint Meeting on Soil and Plant System Sciences (SPSS 2019)—“Natural and Human-Induced Impacts on the Critical Zone and Food Production”

“…Guerrieri et al [ 39 ] highlighted the potential of bacteria isolated from the rhizosphere when processing tomato plants after long-term reduced tillage and cover crop soil management in terms of both their growth-promoting activity and biocontrol of the fungal phytopathogen Sclerotinia sclerotiorum . It must be noted that plant growth-promoting rhizobacteria (PGPR) are gaining increasing relevance among biostimulants to reduce the application of agrochemicals in the framework of sustainable agriculture and tackle crop yield losses due to ongoing climate change [ 40 , 41 ].…”