Phylogenetic diversity of bacterial endophytes of Panax notoginseng with antagonistic characteristics towards pathogens of root-rot disease complex

Abstract

Endophytes play an important role in protection of host plants from infection by phytopathogens. Endophytic bacteria were isolated from five different parts (root, stem, petiole, leaf and seed) of Panax notoginseng and evaluated for antagonistic activity against Fusarium oxysporum, Ralstonia sp. and Meloidogyne hapla, three major pathogens associated with root-rot disease complex of P. notoginseng. From 1000 endophytic bacterial strains evaluated in vitro, 104 strains exhibited antagonistic properties against at least one of these three pathogens. Phylogenetic analyses of their 16S rRNA gene sequences showed that these 104 antagonistic bacteria belong to four clusters: Firmicutes, Proteobacteria, Actinobacteria and Bacteroidetes/Chlorobi. Members of the Firmicutes, in particular the Bacillus spp., were predominant in all analyzed tissues. The root was the main reservoir for antagonistic bacteria. Of the 104 antagonists, 51 strains showed antagonistic activities to one pathogen only, while 43 and 10 displayed the activities towards two and all three pathogens, respectively. The most dominant species in all tissues were Bacillus amyloliquefaciens subsp. plantarum and Bacillus methylotrophicus, which were represented by eight strains with broad antagonistic spectrum to the all three test pathogens of root-rot disease complex of P. notoginseng.

Molecular characterization of microbial communities in the rhizosphere soils and roots of diseased and healthy Panax notoginseng

“…In the future, we should pay more attention to this genus, for species of Pseudomonas acted as one predicted pathogen causing root-rot disease of P. notoginseng. However, root-rot disease was reported to be caused by number of pathogens including bacteria and fungi (Ma et al 2013), and other common microbial pathogens such as Lonsdalea species can't be ignored, which was also more abundant in rhizosphere soils of diseased plants.…”

“…Generally, P. notoginseng is shade cultivated without tillage and is allowed to grow for at least 3 years to develop roots. The long growth period, shaded and humid planting conditions provided suitable environment for the development of several diseases, such as black spot, grey mould, round spot and root rot (Ma et al 2013). Of these diseases, the root-rot disease complex (RRDC) is the most destructive disease affecting P. notoginseng during the whole growth period and could decrease the biological yield by 5-20 %, sometimes exceeding 70 %.…”

Phylogenetic analysis of endophytic bacterial isolates from leaves of the medicinal plant Trichilia elegans A. Juss. (Meliaceae)

“…Bacillus is a Gram-positive, spore-forming, rod-shaped genus with high tolerance to adverse ecological conditions. Previous studies have shown that endophytic bacteria of the genus Bacillus are present in: Coffea arabica L. (Vega et al, 2005), sunflower (Forchetti et al, 2007), cotton (Misaghi and Donndelinger, 1990), potato (Sessitsch et al, 2004), strawberry (Dias et al, 2008), Panaxnoto ginseng (Ma et al, 2013), and citrus plants (Araujo et al, 2001). Among the bioprospection factors, the endophyte Bacillus stands out for phosphate solubilization and auxin production (Dias et al, 2008) and activity against Fusarium oxysporum, Ralstonia sp, and Meloidogyne hapla (Ma et al, 2013).…”

Isolation and Characterization of Endophytic Bacteria Associated with Roots of Jojoba (<i>Simmondsia chinensis</i> (Link) Schneid)

“…This result is considered as positive for siderophore production, showing the capacity to improve iron nutrition in plants, because siderophores are responsible of chelating and transport 3 , and the ability to fix nitrogen 11 . Similarly, four strains that produced siderophores also showed the ability to inhibit the growth of fungi which was likely due to sequestration of iron by bacteria limiting growth of pathogenic fungus 15 . Isolation of microorganisms that have the ability to inhibit growth of pathogenic fungi could be an alternative to reduce economic losses in agriculture 11 .…”

“…Percentage inhibition (PI) was calculated using the formula PI = (DC -DT)/DC  100%, where DC and DT represent the colony diameters of Alternaria sp. on the control and treatments respectively 15 . Jojoba is a shrub found in arid zones with rainfall of 80-120 mm/year, temperature ranging from -5C to 54C and soils with pH 5-8 (ref.…”