Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 17, 2013
Publication Date: February 1, 2013
Repository URL: http://handle.nal.usda.gov/10113/56569
Citation: Funnell-Harris, D.L., Sattler, S.E., Pedersen, J.F. 2013. Characterization of fluorescent Pseudomonas spp. associated with roots and soil of two sorghum genotypes. European Journal of Plant Pathology. 136 (3): 469-481. Interpretive Summary: Fluorescent Pseudomonas bacteria were collected from roots and associated soil of different sorghum cultivars and a wheat cultivar grown in two different soil types. The ability of the bacteria to produce compounds that inhibit fungi that cause diseases in sorghum was determined. Results indicated that both soil type and plant cultivar affected soil bacteria populations that can inhibit sorghum pathogens. Two bacterial isolates or strains found on the sorghum roots and associated soil inhibited the growth of five pathogens. These two isolates have potential as biological control agents for sorghum fungal pathogens.
Technical Abstract: Sorghum is used as bioenergy feedstock, animal feed, and food. Economical methods for disease prevention and control are valuable for producers. Fluorescent Pseudomonas spp. were isolated from sorghum roots and surrounding soil with the goal of finding isolates that significantly inhibited sorghum fungal pathogens. Fluorescent pseudomonads were collected from seedlings of sorghum cultivars RTx433 and Redlan and wheat cultivar Lewjain, grown in two soils. Lewjain is known to support growth of producers of the antibiotic, 2,4-diacetylphloroglucinol (2,4-DAPG). Isolates from all three plants were assessed for hydrogen cyanide (HCN) and extracellular protease production, and for a 2,4-DAPG gene, phlD. Both soil type and plant type affected HCN- and protease-production, but phlD was not affected. Subsets of phlD+ isolates were chosen to determine phlD genotypes and to conduct in vitro inhibition assays against sorghum pathogens. Most isolates from sorghum and wheat were genotype D, previously associated with superior root colonization. phlD+ sorghum isolates were co-cultured with five sorghum pathogens. One isolate from each sorghum line exhibited inhibition to all five pathogens but more Redlan isolates were inhibitory to the virulent pathogen, Fusarium thapsinum, than RTx433 isolates. Nearly all inhibitory isolates from either sorghum cultivar were from one soil type. This is consistent with what had been previously observed in field studies: that soil type played a significant role in determining characteristics of fluorescent Pseudomonas spp. isolated from roots or soil, but sorghum genotype also had a considerable effect.