Clonostachys rosea to control plant diseases

The fungus Clonostachys rosea was recognized as an aggressive parasite on other fungi already in the late 1950s. Research into its potential use in biological control of plant diseases soon followed. Today, there are several commercial products based on C. rosea available for biocontrol applications worldwide. Although its mycoparasitic ability has attracted a lot of interest, C. rosea is now viewed as an ecological generalist whose lifestyle also includes plant endophytism, rhizosphere competence and polyphagous ability. Protocols for producing high amounts of C. rosea spores are available for both solid state and liquid fermentation. Low temperature and low moisture content are key factors that influence the shelf life of C. rosea propagules. Products based on C. rosea can be delivered to flowers using bumble bees, applied by spraying or as seed dressing or by incorporation into the soil. Clonostachys rosea is today an established factor in sustainable plant protection strategies.

Experimental-Evolution-Driven Identification of Arabidopsis Rhizosphere Competence Genes in Pseudomonas protegens

Beneficial root-associated microorganisms carry out many functions that are essential for plant performance. Establishment of a bacterium on plant roots, however, requires overcoming many challenges.

An Overview of Metabolic Activity, Beneficial and Pathogenic Aspects of Burkholderia Spp

Burkholderia is an important bacterial species which has different beneficial effects, such as promoting the plant growth, including rhizosphere competence for the secretion of allelochemicals, production of antibiotics, and siderophores. In addition, most of Burkholderia species have demonstrated promising biocontrol action against different phytopathogens for diverse crops. In particular, Burkholderia demonstrates significant biotechnological potential as a source of novel antibiotics and bioactive secondary metabolites. The current review is concerned with Burkholderia spp. covering the following aspects: discovering, classification, distribution, plant growth promoting effect, and antimicrobial activity of different species of Burkholderia, shedding light on the most important secondary metabolites, their pathogenic effects, and biochemical characterization of some important species of Burkholderia, such as B. cepacia, B. andropogonis, B. plantarii, B. rhizoxinica, B. glumae, B. caryophylli and B. gladioli.

Plant cell wall polysaccharides induce colony expansion of soil-derived Flavobacterium spp.

SummaryFlavobacterium is a genus, belonging to the Bacteriodetes phylum, characterized by a unique gliding motility. They are often abundant in root microbiomes of various plants, but the factors contributing to this high abundance are currently unknown. In this study, we evaluated the effect of various plant-associated poly- and mono-saccharides on colony expansion of two Flavobacterium strains. Both strains were able to grow on pectin and other polysaccharides such as microcrystalline cellulose. However, only pectin, a major component of plant cell walls, substantially enhanced colony expansion on solid surfaces in a dose- and substrate-dependent manner (but did not occur on pectin monomers). On pectin, flavobacteria exhibited a bi-phasic behavior, with an initial phase of rapid expansion, followed by growth within the colonized area. Proteomic and gene expression analyses revealed significant induction of carbohydrate metabolism related proteins when flavobacteria were grown on pectin, including selected SusC/D, TonB-dependent glycan transport operons. Our results suggest an unknown linkage between specific glycan associated operons and flavobacterial colony expansion. This may be associated with their capacity to rapidly glide along the root and metabolize plant cell wall carbohydrates, characteristics that are crucial to rhizosphere competence.Originality-Significance StatementThis study reveals unique data linking plant glycan metabolism and bacterial motility, providing insight into bacterial-root associations and rhizosphere competence. Specifically, it explores mechanisms associated with pectin-stimulated colony expansion in root-associated Flavobacterium strains. We determined that expansion of colonies on pectin was biphasic in nature, characterized by rapid proliferation followed by biomass accumulation. We demonstrate by proteomic and gene expression analyses that expansion of Flavobacterium on pectin strongly induces TonB related transporters, which seemingly play a role in motility in addition to the uptake and metabolism of plant-associated glycans.

Rhizosphere competence of native Rhizobium rhizogenes strain and its use in management of crown gall

Native Rhizobium rhizogenes strain UHFBA-212 [141/1A (NCBI: KC488174)]was isolated from rhizosphere soil of peach nursery plant of wild peach collected from Himachal Pradesh. In addition to this,159 isolates were also collected and were screened in vitro for their biocontrol potential against Agrobacterium tumefaciens. Out of these strain, UHFBA-212 showed maximum zone of inhibition i.e. 4.16 and 3.57cm without and after exposure to chloroform against C58.Sequence analysis (16SrDNA) of the strain showed nucleotide homology similar to Rhizobium sp. Amplification of total genomic DNA of the strain with Vir D2 andipt primers didn’t showed amplification with these virulence genes suggesting the absence of tumorigenic factors. In the field conditions, maximum population (329.33x106 cfu/g of soil) was observed in antibiotic resistant mutant of R. rhizogenes strain K84 applied on cherry rootstock Colt followed by 285.33 (x 106 ) cfu/g of soil in UHFBA-212 after 9 months at the time of uprooting of plants when applied alone as root dip. Minimum incidence of crown gall (2.00%) was observed in strain UHFBA- 212 co inoculated with strain C58 as seed treatment on behmi seeds. The data on population indices in rhizosphere and incidence of crown gall further suggested that for better management of disease R. Rhizogenes isolates should be either equal or more in population than that of A. tumefaciens isolates. Strain UHFBA-212 controls crown gall as effectively as strain K84 and can be exploited against tumorigenic isolates under field conditions.

Rhizosphere Competence of Wild-Type and Genetically Engineered Pseudomonas brassicacearum Is Affected by the Crop Species

2,4-Diacetylphloroglucinol (2,4-DAPG)-producing Pseudomonas brassicacearum Q8r1-96 is a highly effective biocontrol agent of take-all disease of wheat. Strain Z30-97, a recombinant derivative of Q8r1-96 containing the phzABCDEFG operon from P. synxantha (formerly P. fluorescens) 2-79 inserted into its chromosome, also produces phenazine-1-carboxylic acid. Rhizosphere population sizes of Q8r1-96, Z30-97, and 2-79, introduced into the soil, were assayed during successive growth cycles of barley, navy bean, or pea under controlled conditions as a measure of the impact of crop species on rhizosphere colonization of each strain. In the barley rhizosphere, Z30-96 colonized less that Q8r1-96 when they were introduced separately, and Q8r1-96 out-competed Z30-96 when the strains were introduced together. In the navy bean rhizosphere, Q8r1-96 colonized better than Z30-97 when the strains were introduced separately. However, both strains had similar population densities when introduced together. Strain Q8r1-96 and Z30-97 colonized the pea rhizosphere equally well when each strain was introduced separately, but Z30-97 out-competed Q8r1-96 when they were introduced together. To our knowledge, this is the first report of a recombinant biocontrol strain of Pseudomonas spp. gaining rhizosphere competitiveness on a crop species. When assessing the potential fate of and risk posed by a recombinant Pseudomonas sp. in soil, both the identity of the introduced genes and the crop species colonized by the recombinant strain need to be considered.