association of pseudomonas fluorescens - plant … new zealand institute for plant & food...

The New Zealand Institute for Plant & Food Research Limited

S.F. Chng, M.G. Cromey, A. Stewart, S. Dodd and M.V. Jaspers, Sean Bithell

Association of Pseudomonas fluorescenswith take-all suppressive soils in

New Zealand


Take-all

•Gaeumannomyces graminis var. tritici or Ggt•Root disease of autumn-sown wheat in NZ


Take-all

Blackening of the roots and stem bases of wheat plants

Take-all patch with whiteheads


Take-all

•Chemical control impractical•Fungus relies on host remains for survival•Commonly controlled by:

» avoiding growing susceptible hosts in the same field for > 2 seasons.

» continuous growing wheat to induce Take-all decline (TAD).


Take-all decline

•A naturally occurring take-all suppressive phenomenon


Pseudomonas fluorescens

•Buildup of Pseudomonas fluorescens during wheat monoculture•P. fluorescens implicated in development of take-all decline (TAD)


Successive sowing of wheat

•Controlled environment experiment•Four soils in 2nd to 4th yr of wheat•High Ggt DNA concentrations (pg/g soil) and high disease incidence •Sown with wheat•Maintained in a growth chamber for 4 weeks•Population of P. fluorescensassessed. •Process repeated every 4 weeks for seven times.


P. fluorescens

Successive sow ing of w heat

1 2 3 4 5 6 70

1

2

3

4

5

6

7

8

Num

bers

of P

seud

omon

as fl

uore

scen

sC

FU/g

root

s


In suppressive soils

•Another controlled environment study, which identified take-all suppressive soils•Soils exhibiting characteristics of take-all suppression•The microorganisms that might be associated with the different forms of suppression in the rhizosphere characterised using denaturing gradient gel electrophoresis (DGGE)•Forms of suppression

» Specific » General


Bacterial populations in the rhizosphere

General bacterial population Actinomycota

•Consistent between pot reps within a soil•Varied between soils with different forms of suppression


Specific microbes

• Differentiating specific form of suppression from general form of suppression– Pseudomonas fluorescens and P.

putida, Nocardioides oleivorans, Gibberella zeae and Penicillium allii


Chertsey ‘cereal break’ trial

•Effects of different hosts before wheat on take-all and Ggt DNA concentrations (SARDI)•Four cereal species: wheat, barley, triticale and rye•+/- Ggt inoculation•Fallow as a control•Four reps •Total = 40 plots•Take-all severity, pre-sowing and post-harvest Ggt DNAconcentrations were assessed.


Results (back-transformed means)

Year 2008/09 2009/10

CerealsGgt

inoculation TAI

Post- harvest Ggt DNA(pg/g soil)

TAI in sub. wheat

Post-harvest Ggt DNA(pg/g soil)

Barley - 0.5 14 0.4 1.2

Ryecorn - 0 170 25.7 32.0

Triticale - 0.9 120 29.5 16.6

Wheat - 1 161 8.8 14.3

Fallow - 8 1.7 2.5

Barley + 7.7 368 0.2 5.7

Ryecorn + 0 851 13.2 38.1

Triticale + 3.7 517 18.7 53.2

Wheat + 9.6 49 0.8 14.0

Fallow - 5 0.4 2.0


)

Barley Rye Triticale Wheat Fallow

105

106

107

108

109

1010Not InoculatedInoculated

Pseudomonas fluorescens

Num

bers

of P

seud

omon

as fl

uore

scen

sC

FU /g

root

s


Where to from now

•The importance of other micro-organisms on take-all suppression in the last study is yet to be confirmed (waiting for results on 454 sequencing).

•All these results have collectively suggest the likely association of P. fluorescens with take-all suppressive soils in New Zealand.

•Current research investigates the microbial population shift, residue breakdown and Ggt DNA /inoculum concentrations over time and their effects on disease suppression.


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association of pseudomonas fluorescens - plant … new zealand institute for plant & food...

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