Organic and Sustainable Farming 11:00-12:30 Capturing the Organic Market

2:00-3:00 Organic Pest Management

4:30-5:30 Alternative Soil Management

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Soil Health and Disease Suppression in organic versus conventional plant production

Prof. Dr. Ariena van Bruggen Emerging Pathogens Institute and Plant Pathology Dept. University of Florida in Gainesville, FL

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Outline:

  Organic and conventional crop management, soil quality and soil health

  Root disease suppression in organic compared to conventional soil

  Root diseases in crop mixtures versus pure stands   Nematode suppression in organic soils   Suppression of human pathogens in organic soils   Reasons for pathogen suppression in organic soils   Conclusions

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Differences between conventional and organic management Conventional   synthetic pesticides

  synthetic fertilizers

  short rotation

  rarely cover crops

  rarely plant mixtures

  sometimes biological control

(fungi, bacteria) applied

  sometimes soil disinfestation

Organic

  natural and mineral pesticides

  organic amendments

  longer rotation

  frequently cover crops

  more frequently plant mixtures

  rarely biocontrol applied

  rarely soil disinfestation

(by heat)

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Differences between conventional and organic management: agrobiodiversity

  Differences in plant diversity in time and space can have a major influence on plant diseases

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Org - Conv Org - Conv

Photographs by Frans Smeding

Differences between conventional and organic soils

Conventional   pesticide residues   high NO3 and P2O5 contents   low organic matter content   poor structure   lower microbial diversity and activity   lower soil animal diversity and numbers   conduciveness to root diseases

Organic   no pesticide residues   low NO3 and P2O5 contents   higher organic matter content   sometimes better structure   higher microbial diversity and activity   higher soil animal diversity and numbers   suppressiveness to root diseases

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Soil quality and soil health

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Quality: mainly physical and chemical characteristics Health: mainly biological characteristics; diversity, ability to withstand stress

  Left: old grassland, no fertil.   Right: reseeded, fertilizer

  Left: good quality soil, crumbly   Right: poor quality soil, blocky

Photo’s on the right by Jan Bokhorst

Tomato corky root severity in organic, low-input and conventional plots in California

  ORG, LOW and CONV 4-yr rotations, CONV2 a 2-yr rotation   Effects of rotation and of management were significant

Corky root

0

4

8

12

16

20

Year 8 Year 9

Lesi

ons/

root

sys

tem

ORG LOW CONV CONV2

EPI Van Bruggen et al., unpubl.

Tomato root rot by Pythium in organic, low-input and conventional plots in California

0

10

20

30

40

1997 1998

% ro

tted

tips/

root

sys

tem

Pythium root rot

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  ORG, LOW and CONV 4-yr rotations, CONV2 a 2-yr rotation   Effects of rotation and of management were significant

Year 8 Year 9

Van Bruggen et al., unpubl.

Take-all disease on barley in conventional and organic soils

BARLEY 0% INOCULUM

0

2

4

6

C-C C-S O-C O-S

DIS

EASE

RA

TIN

G

BARLEY 0.5% INOCULUM

0

2

4

6

C-C C-S O-C O-S

DIS

EA

SE

RA

TIN

G

Hiddink et al., 2005

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  Less disease in organic than in conventional soil

  Pseudomonas fluorescens was not responsible for disease suppression in organic soils

Relation between take-all disease on triticale and bacterial diversity in conventional, transitonal and organic soil

0

2

4

6

C-L CO-S O-S

Dis

ease

ratin

g

0

50

100

85 90 95 100Relative diversity index

Rel

ativ

e di

seas

e

Hiddink et al., 2005

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  Greater microbial diversity in organic soil

  was associated with less take-all disease

Effects of plant diversity on root diseases

0.0

20.0

40.0

60.0

80.0

100.0

2001 2002 2003

% D

isea

sed

root

s

TriticaleTriticale-clover

0.0

1.0

2.0

3.0

4.0

5.0

2001 2002 2003

NO

3 m

g/kg

soi

l TriticaleTriticale-clover

Take-all disease severity on triticale alone or in a mix with clover

Soil NO3 content in a triticale crop or in a mix with clover

Hiddink et al., unpubl.

EPI Hiddink et al., unpubl.

Effects of plant diversity on root diseases

0.010.020.030.040.050.060.070.080.0

2001 2003

% D

iseased p

lants B.SPROUTS

MIX

Clubroot incidence on Brussels sprouts grown alone or in a mix with barley

Hiddink et al., unpubl.

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Effects of soil heating by steam on relative survival of J2 juveniles of root knot nematode (Meloidogyne incognita) in organic greenhouse soils

Berkelmans et al., unpubl.

EDECDCDCDCCC

BAB

ABABAAA

00,10,20,30,40,50,60,70,8

N M E Q B I X Y S G D O F C LGreenhouse soils

J2 s

urvi

val (

unpa

st/p

ast)

Steamed in past Never steamed

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  Root knot nematode larvae were more suppressed in nonsterilized soil

  Slow-growing predatory nematodes did not come back in steamed soil

Effects of soil heating by steam on root knot nematode index (RKI) in pots inoculated with J2 of M. incognita

Berkelmans et al., unpubl.

00,5

11,5

22,5

33,5

44,5

55,5

control L O M S F I

Farmers

RK

I (m

ed

ian

)

A

B BC

D C

C BC

Steamed in past

Never steamed

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  Root knot nematode index was lower in nonsterilized soil

  Slow-growing predatory nematodes did not come back in steamed soil

Risk of human pathogens in food production systems

Most cases/outbreaks linked to animal products

Increased association between food-borne diseases and fresh vegetables

manure

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Franz et al., 2008

Klerks et al., 2007

Salmonella

Reservoirs: cows pigs chickens Salmonella low medium high E. coli O157:H7 high low low Campylobacter low medium high

Survival of E.coli O157:H7 in manure and soil

Risk of human pathogens in food systems

Time (days)

0

1

2

3

0 20 40 60 Time (days)

log

CFU

/gdw

org/sand conv/sand org/clay conv/clay

0

1

2

3

4

5

6

7

log

CFU

/gdw

GMH

GH

SH

GML

GL

SL

0 20 40 60

EPI Franz et al., 2005

  E. coli O157:H7 declined faster in fibrous manure from cows on a high fiber diet (with straw) than on a low fiber diet (with corn silage)

  E. coli O157:H7 declined faster in organic than in conventional soil

Internalization of Salmonella in tomato plants

  Salmonella declined faster in leaves of plants in organic than in conventional soil

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BSL II greenhouse

0 1 2 3 4 5 6 7 8 9

One-week post inoculation

Two-week post inoculation

log

CFU

/gdw

Salmonella Typhimurium inside inoculated leaflets. Green=sand; Red=conventional soil; Yellow=organic soil

Gu et al., 2011

Internalization of Salmonella in tomato plants

  Salmonella declined faster in organic soils   Decline rates were higher at higher bacterial diversity and Ca and Mg

concentrations in soil

Correlation of decline rates with bacterial diversity and soil nutrients

EPI Gu et al., 2012

Internalization of Salmonella in tomato plants

A trichome (leaf hair) and a stomate (leaf opening) with Salmonella cells

The tip of a leaflet with hydathode; Salmonella cells inside leaf and conducting vessels

Water droplets emerging through hydathodes (openings) on the margins of leaflets

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Salmonella enters a leaf through stomates or hydathodes (different kinds of openings for movement of gas and liquid)

Gu et al., unpubl.

Internalization of Salmonella in tomato plants

Conducting tissues: xylem on left and phloem on right (in box)

Phloem cells with Salmonella cell inside

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Salmonella moves from leaves into stems (phloem) and fruit

Gu et al., 2011

Internalization of Salmonella in tomato plants

contaminated fruits control fruits

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Salmonella inside tomato fruits on leaf-inoculated plants

Gu et al., 2011

Internalization of Salmonella in tomato plants

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Gu et al., 2012

  1 Number of plants with internally contaminated leaves   2 Number of fruits that were internally contaminated, 9 fruits on 1 plant   3 Number of fruits that were internally contaminated, 5 fruits on 1 plant,

2 fruits on another plant.

Reasons for pathogen suppression in organic soils

  In the soil and rhizosphere   Greater diversity of microbiota (bacteria, fungi, nematodes etc.) ->

a greater chance of the presence of antagonists and predators   Root exudates consumed by abundance of microbes -> no

rhizosphere effect -> pathogens cannot find roots   Fewer nutrients and substrate available for pathogens to grow

  In the plants   Lower nitrogen levels, higher Mg and Ca levels -> sturdier plants   Greater induced resistance throughout the plants   Better soil structure, drainage, water-holding capacity -> less

stressed plants

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Similarity of microbial communities in rhizosphere versus bulk soil from organic and conventional farms ‚‚3ˆB‚‚BRR‚R2ˆBBRR‚BBBRR‚BRBBRRBR‚BBRRRRR1ˆBBBBRBR‚BBBBBR‚BBBRBBRRRR‚BRRR0ˆRRR‚RRRR‚RRRB‚RB‐1ˆRRRRBRR‚RBBR‚R‚B‐2ˆB‚‚BBBB‚B‐3ˆ‚‚BB‚‐4ˆBB‚B‚B‚‐5ˆ‚B‚‚‐6ˆ‚Šƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒ‐6‐4‐202468

R Conventional Rhizosphere samples B Conventional Bulk Soil samples R Organic Rhizosphere samples B Organic Bulk Soil samples

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Bacterial composition 1

Bac

teria

l com

posi

tion

2

Van Diepeningen et al., 2006

Each dot is a soil sample

Conclusions

  Usually: root disease severity is lower in organic than in conventional farms

  Frequently: a positive correlation of root disease severity with N availability, and a negative correlation with microbial activity and diversity

  Usually: soil sterilization has a long-term negative effect on natural pathogen and nematode suppression

  Commonly: enteric pathogens are suppressed in fibrous manure and well aerated (organic) soil

  Rarely: enteric pathogens can enter through roots or leaves, move inside the plant and contaminate a plant internally

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Conclusions

  Survival and movement of Salmonella in tomato plants is less in organic than conventional soil

  Greater bacterial diversity in plants grown in organic soils may lead to greater resistance to internal colonization of Salmonella as well as plant pathogens

  It is important to maintain soil health by diverse cropping systems, addition of organic matter to soil, and avoidance of any kind of soil sterilization (soil solarization and biological soil disinfestation are ok)

  It is important to prevent contamination with human pathogens: properly composted manure, clean water

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Acknowledgements

  University of California Davis: all people of the SAFS project, especially Howard Ferris, Kate Scow, Sean Clark

  Wageningen University: Aad Termoshuizen, Wim Blok, Gerbert Hiddink, Anne van Diepeningen, Robert Berkelmans, Eelco Franz, Michel Klerks, Oscar de Vos

  University of Florida: Ganyu Gu, Juan Cevallos-Cevallos, Ellen Dickstein

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