Ipm03_larkinbcimpact

BIOCONTROL FUNGI FOR CONTROL OF PLANT PATHOGENS: A WHOLE DIFFERENT BIOCONTROL GAME ROBERT LARKIN USDA-ARS, New England Plant, Soil, and Water Lab Orono, ME

Biocontrol of plant pathogens and disease is fundamentally different from biocontrol of weeds, insects, or other animals. Emphasis is placed on disease control rather than pathogen control, and in some cases the pathogen is not targeted at all. Thus, very different characteristics are involved, and this biocontrol only rarely resembles the traditional approach of using debilitating pathogens or parasites to destroy a target organism. These characteristics have important implications on the potential impacts of these biocontrol agents and approaches.

Biocontrol Fungi for Control of Plant Pathogens I. Introduction II. Distinctive Characteristics III. Organisms Used IV. Approaches Used V. Impacts

Distinctive Characteristics of Biocontrol of Plant Pathogens  Diverse mechanisms of action  Competition  Antibiosis  Parasitism/Predation  Induced Resistance

 May not directly attack target pathogen  Protection of specific infection sites  Inhibition or suppression of activity  Induce defense responses

 Limited access to pathogen (soilborne)  Soil incorporation  Short-term survival in soil

Biocontrol Fungi Used

Control of

 Trichoderma spp. Seed, stem, root rots,  harzianum, virens Pythium, Rhizoctonia,  hamatum, atroviride, koningii Fusarium, many others

 Coniothyrium minitans

Sclerotinia spp.

 Fusarium oxysporum (nonpath.strains)

Fusarium wilt

Others Gliocladium catenulateum Ampelomyces quisqualis Candida oleophila Sporidesmium sclerotivorum

Paecilomyces lilacinus Phlebia gigantea Pythium oligandrum Penicillium spp.

Approaches to minimize inundative applications  Site-specific applications  Seed Treatments  Transplant treatments  In-furrow application

 Strain selection and enhancement  Rhizosphere competence – T. harzianum  Antibiotic production – T. virens  Efficacy at reduced inoculum rates – F. oxysporum

 Manipulation of environment (favorable for biocontrol)  Rotations, amendments, nutrients  Solarization

Effect of inoculum density of two different biocontrol strains on control of Fusarium wilt

Wilt incidence (%)

100

CS-20 Fo47

80 60 40 20 0 1

10

100

1,000

10,000 100,000

Biocontrol CFU/g soil Larkin and Fravel, 1996

Approaches to minimize inundative applications  Site-specific applications  Seed Treatments  Transplant treatments  In-furrow application

 Strain selection and enhancement  Rhizosphere competence – T. harzianum  Antibiotic production – T. virens  Efficacy at reduced inoculum rates – F. oxysporum

 Manipulation of environment (favorable for biocontrol)  Rotations, amendments, nutrients  Solarization

Impact of Biocontrol Fungi

(unintended effects)

From Cook et al., 1996 (Biological Control 7:333)  Displacement of nontarget organisms

 Allergenicity (humans, animals)  Toxigenicity  Pathogenicity

Impacts Displacement of nontarget organisms  Beneficial organisms  Changes in soil microbial characteristics  Population dynamics  Functional attributes  Structural attributes

 BCA recovery  high root colonization  low soil populations

Soil Microbial Characteristics Current Research - Biocontrol of Rhizoctonia solani (stem canker and black scurf) on Potatoes  Trichoderma harzianum (T-22)  Trichoderma virens (Gl-21)  Pathogen inoculum (85 kg/ha ) prior to planting.  Biocontrol - In-furrow application at planting.  Other treatments:  Bacterial agents (Bacillus subtilis, Burkholderia cepacia)  Chemical seed treatment (Evolve)  Chemical/biological treatment (Evolve/Bcep)  Nontreated & Path-treated control

 Soil microbial characteristics assessed at end of season (post-harvest)

CFU/g soil (x10 4 ) CFU/g soil (x106 )

Soil bacteria and pseudomonas populations after biocontrol treatments (end of season) ) 50

Bacteria

40 30 20

T.har

10

T.vir

0

120 100 80 60 40 20 0

a

Pseudomonas ab ab ab b

Evolve No Path Path

CFU/g soil (x106 )

Soil fungi and Trichoderma populations following biocontrol treatments (end of season) 60 40

T.har

20

T.vir 0

CFU/g soil (x106 )

Fungi

3 2.5

a

ab

2 1.5 1 0.5 0

Evolve

Trichoderma ab b

ab

No Path Path

Soil microbial activity following biocontrol treatments (end of season) 0.6 Optical Density

a

0.55 0.5

ab

ab

ab

bc bc c c

0.45 0.4

Microbial activity

T.har T.vir Evolve Ev/Bcep B.subtilis B.cepacia No Path Path

Soil Microbial Characteristics (after one field season – potato crop)  Functional attributes

 Substrate utilization assays  no consistent effects  chemical- lower for some substrate groups  Structural attributes  FAME profiles  no overall effects  no major shifts in microbial communities  no change in biomarkers

Impacts  Allergenicity (humans & other animals)

 no direct evidence (none found)  dusts in manufacturing, application  Toxigenicity (nontarget)  plants (phytotoxins)  other microorganisms  Pathogenicity other crop plants other microrganismsmycoparasites

CONCLUSIONS  Biocontrol of plant pathogens is distinctly different from traditional biological control , involving different mechanisms, effects, and approaches, resulting in different challenges and different types of potential impacts.  Most probable impacts are on nontarget root and soil microbes and plants. Most effects observed on and around roots. Few residual effects observed in soil.  Rigorous strain selection, site-specific application, and move towards inoculative or augmentive applications can limit potential nontarget impacts.  Overall, long-term and/or adverse effects appear minimal. Although much more information needed.