1. Disease Management by Biocontrol

2. Biocontrol of Heterobasidion annosum by Phlebiopsis gigantea
H. annosum > root and butt rot of conifer (Heterobasidion root rot)
> infect freshly cut pine stump and then spread into the roots.
> through root contact > spreads into roots of standing trees
Root and butt rot

3. > stump surface is inoculated with oidia of P
> stump surface is inoculated with oidia of P. gigantea immediately after the tree is felled > Phlebiopsis occupies stump and spread into the lateral roots.
> competes for food and space with Heterobasidion, and exclude the pathogen.

4. Biocontrol of Chestnut Blight / Canker with Hypovirulent strains of the pathogen
- Hypovirulence > pathogen strain which has become avirulence
> Chestnuts blight fungus - Cryphonectria parasitica.

5. Chesnut blight > is controlled naturally through inoculation of cankers with hipovirulent strains of the same fungus
France and Italy
> the hipovirulent strains carry virus-like double stranded RNAs > limits the pathogenicity of the virulent strain

6. Biocontrol of Soilborne Pathogens by Hyperparasitism / Mycoparasitism
- Hyperparasitism - parasitism on another parasite.
mycelium, resting spores, or sclerotia of pathogenic soil fungi (Pythium, Phytophthora, Verticillium, Rhizoctonia, and Sclerotium) >> are invaded and parasitized or lysed by several non-pathogenic fungi.
- example > hyperparasitism involves the mycoparasitic Trichoderma spp. on Rhizoctonia solani

7. SEM - surface of a hyphae > Rhizoctonia solani (pathogen) after mycoparasitic Trichoderma hyphae were removed. Holes >> Trichoderma hyphae penetrated the R. solani. Erosion of the cell wall > activity of cell wall degrading enzymes from Trichoderma
Mycoparasitism by a Trichoderma strain (yellow) on Pythium (green) on the surface of pea seed.

8. Biocontrol of Soilborne Pathogens with Mycorrhizae
Mycorrhizae > fungi that have symbiotic association with the roots of plant.
> colonize roots intercellularly (ectomycorrhizae) or intracellularly (endomycorrhizae)

9. Endo (VAM)
Ecto

10. Mycorrhizae obtain organic nutrients from the plant
benefit the plant > promoting nutrient uptake and enhancing water transport
sometimes providing the plant with protection against several soilborne pathogens.
- Mycorrhiza > provide considerable protection to pine seedlings from Phytophthora cinnamomi, to tomato and Douglas fir seedlings against F. oxysporum.

11. Biocontrol using Trap Plants
Trap plants > to protect other plants from attack by insect > aphids which are vectors for virus diseases.
- Corn (tall plant) planted around field of smaller plants (pepper or melon) >> incoming aphids carrying viruses that attack pepper or melon will first stop and feed on the corn >> the virus are non persistant - their virulence were lose before they could invade the host

12. Trap Plants

13. Application of Biocontrol Agent
Application will depend on the type of pathogen and the environmental conditions.
Can be used as:
> Soil treatment
> Seed treatment
> Foliage spray/paint

14. Examples of Biocontrol Agent

15. Bacillus subtilis GB03 (Gram positive)
target pathogens > fungi that attack plant roots – Rhizoctonia, Fusarium, Alternaria, Phytophthora >> root and seed rots, seedling diseases
Mechanism of biocontrol > B. subtilis colonizes plant roots and promote growth
> also produce volatiles > induce systemic response and antibiotics
Application – seed treatment (mix the bacteria with seeds)

16. Pseudomonas syringae ESC-10 and ESC-11
(Gram positive)
Target pathogens :
> postharvest pathogens – Botrytis cinerea, Penicillium spp., Mucor pyroformis, Geotrichum candidum;
> potato pathogen – Fusarium sambucinum, Helmintosporium solani

17. Mechanism of biocontrol :
competition > primary mechanism
produce antibiotic > syringomycin (minor role)
Application:
Commodities > harvested and cleaned > solution containing P. syringae is applied > spraying or dipping the produce in the solution

18. Trichoderma harzianum KRL-AG2 (T-22)
Target pathogens : soilborne pathogens
Cylindrocladium, Fusarium, Pythium, Rhizoctonia solani, Sclerotinia, Thielaviopsis basicola >> damping-off, root rot
Mechanism of biocontrol:
mycoparasite > rapidly colonize plant roots > out-competing pathogens for nutrients and space
promote plant growth

19. Application :
T. harzianum > formulated as granule
> mixed with seed or incorporated into soil
> mixed with water and applied as a drench

20. Muscodor albus QST 20799
non-spore forming fungus
Target pathogens > bacteria, fungi, nematodes >> various diseases of field, greenhouse, stored crops, cut flowers
Mechanism of biocontrol:
produce volatile organic compound > antimicrobial
Application > incorporated into soil
> added to containers

21. Agrobacterium radiobacter strain K1026
(Gram negative)
Target pathogens :
Agrobacterium tumefaciens, A. radiobacter
> crown gall of fruits (apricot, cherry, peach) and nuts (almond, pecan, walnut)
Mechanism of biocontrol:
- produce bacteriocin agrocin 84 > antimicrobial activity
- competes with crown gall pathogen for nutrients and attachment sites on plant roots

22. Application :
- cells of A. radiobacter (produced in culture medium) > suspended in nonchlorinated water > applied to seeds, seedlings, cuttings, roots, stems and as soil drench