Plant Pathogens: Fungi, Bacteria, Viruses & Soil Treatments

Posted on Jan 30, 2025 in Biology

Plant Pathogens Affecting Crops

Fungi Affecting Roots

  • Fusarium proliferatum: Affects asparagus.
  • Rhizoctonia solani
  • Sclerotinia sclerotiorum: Affects artichokes, sensitivity to pig slurry N.
  • Phytophthora cactorum: Affects strawberries and carrots.
  • New pathogen: Fusarium oxysporum in Spain (report to authorities).

Fungi and Bacteria Affecting Vascular System

  • Fusarium oxysporum fsp cyclaminis: Affects cyclamen in Madrid.
  • F. oxysporum fsp dianthi: Affects carnation in Almeria, related to sheep manure.
  • Fusarium wilt: Affects melon.
  • Peronospora tabacina: Mildew of pepper, parasitized whitefly by Encarsia formosa.

Viruses

  • Tomato spotted wilt virus: Affects artichokes, peppers, lettuce, thrips flowers. Similar molecule to the AIDS virus.
  • Potato virus Y: Affects pepper, purple veins on the underside, transmitted by aphids.
  • Mosaic virus: Seed-borne and contact transmission.
  • Spoon virus: More damage in tomatoes, transmitted by Bemisia tabaci (whitefly), leaflets shrink and curl.
  • PepMV satellite virus: Associated with meat 5.
  • False symptoms of virus infection: Eggplant by white spider (mite). Eggs visible. Use sulfur.

Other Soil Issues

  • Phytophthora capsici: Soil fungus, needs water to multiply, causes root and stem rot with over-watering.
  • Meloidogyne incognita: Root-knot nematode, causes lumps, hyperplasia, tissue swelling, root dysfunction, yellowing and stunting.

Soil Disinfection Methods

Steam Disinfection

  • Advantages: Broad action, immediate planting.
  • Disadvantages: Rapid recolonization, high energy consumption, phytotoxicity, high investment.

Mechanical Disinfection

  • Advantages: Green manure, field preparation.
  • Disadvantages: Resistant structures remain, high power consumption.

Fumigants

  • Chloropicrin: 50g/m2, toxic, requires trained staff.
  • Metam-sodium: 150g/m2, drip application.
  • Dazomet: Decomposes to methyl isothiocyanate, tablets need to decompose.
  • Propylene-oxide: Unauthorized, explosive, and carcinogenic. 600l/ha. Ineffective in strawberry trials.
  • Dimethyl disulfide: Ineffective, comparable to untreated control.
  • 1.3-dichloropropene + chloropicrin (Telone): Liquid, requires trained staff.
  • Proper soil preparation is crucial for fumigant penetration.
  • Use of plastic hoses and buried edges to prevent gas escape.
  • Irrigate 2-3 days before application and after to seal with water.
  • Seal with plastic for 21 days during the hottest period.
  • 1.3-dichloropropene also acts as a herbicide against purple purslane.
  • Produces similar results to BM, accepted as an alternative.
  • Limited use within a certain area.

Action on Charred Soil

  • Improves soil bulk density, increasing irrigation infiltration.
  • No change in soil electrical conductivity or salt concentration.
  • Slightly decreases pH in calcareous soils (pH > 8).
  • Increases organic matter.
  • No change in Na and Cl levels.
  • Increases K and Mg, improving production.
  • Increases N, dependent on C/N ratio.
  • Increases soluble Fe, preventing chlorosis.
  • Increases Cu and Zn.
  • Increases soluble P.
  • No change in B.
  • Biosolarization destroys allelopathic substances.

Antagonistic Fungi and Compost

Antagonistic Fungi

Trichoderma, Verticillium, Gliocladium, and others.

Compost

Incorporation of beneficial microorganisms. 4compost: Alperujo, mushrooms, cork, grape pomace.

Use compost and manage soils to multiply microbes, as used in biosolarization, increases and improves the soil, and controls diseases.

Compost Advantages

  • Low cost, reuse of agro-industrial waste.
  • High organic matter content.

Compost Disadvantages

  • Heterogeneity.
  • Potential pathogenic organisms for humans.
  • Salinity.