How to Read Disease Resistance Codes in Seed Catalogs and Seed Packets

ByStephen Albert

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Seed catalogs and seed packets often list short codes after a variety name—such as V, F1, or PM. These codes tell you what diseases the variety can tolerate, resist, or avoid. Understanding them helps you choose crops that will thrive in a regenerative garden with fewer inputs and better long-term health.

What “Resistance” Really Means

Disease resistance does not mean a plant will never get sick. It means the plant can:

  • Tolerate infection with minimal damage,
  • Slow or limit disease spread, or
  • Recover more quickly under stress.

This fits perfectly with regenerative principles: fewer interventions, fewer chemicals, and plants that stay productive in real-world conditions.

Two Types of Resistance

HR – High Resistance

  • The plant can strongly limit disease development.
  • Symptoms may appear but typically stay mild.

IR – Intermediate Resistance

  • The plant slows disease progress but may show moderate symptoms under pressure.

Both types help reduce crop loss—HR simply offers a stronger buffer.

Common Disease Resistance Codes by Vegetable

Below are the codes you’ll see most often across seed catalogs:

Tomatoes

  • V – Verticillium Wilt
  • F / F1 / F2 – Fusarium Wilt Races 1 or 2
  • N – Root-knot Nematodes
  • T / TMV / ToMV – Tobacco Mosaic Virus
  • LB – Late Blight
  • EB – Early Blight
  • TSWV – Tomato Spotted Wilt Virus
  • Cl – Cladosporium leaf mold

A tomato listed as VFN is resistant to verticillium, fusarium (race 1), and root-knot nematodes.

Cucumbers

  • PM – Powdery Mildew
  • DM – Downy Mildew
  • ALS – Angular Leaf Spot
  • CMV – Cucumber Mosaic Virus
  • Sc – Scab

A cucumber marked PM, DM, CMV has broad resistance to the big three diseases of humid climates.

Squash & Pumpkins

  • PM – Powdery Mildew
  • WMV – Watermelon Mosaic Virus
  • ZYMV – Zucchini Yellow Mosaic Virus
  • PRSV – Papaya Ringspot Virus
  • CMV – Cucumber Mosaic Virus
  • Sc – Scab

Many modern hybrids stack multiple virus resistances—helpful in summer squash where virus pressure is high.

Melons

  • PM – Powdery Mildew (look for races, e.g., PM 1, PM 2)
  • FW – Fusarium Wilt
  • Gsb – Gummy Stem Blight
  • PRSV / ZYMV / WMV / CMV – Viral diseases common in cucurbits

Peppers

  • TMV – Tobacco Mosaic Virus
  • PVY – Potato Virus Y
  • TEV – Tobacco Etch Virus
  • X – Bacterial Leaf Spot (various races, e.g., X10–X5)
  • CMV – Cucumber Mosaic Virus

Beans

  • BCMV – Bean Common Mosaic Virus
  • BCTV – Beet Curly Top Virus
  • Cl / C – Anthracnose
  • U – Rust

Lettuce

  • DM – Downy Mildew (specific races listed, e.g., DM 1–35)
  • TB – Tipburn tolerance
  • LMV – Lettuce Mosaic Virus

Brassicas (Broccoli, Cabbage, Kale)

  • F – Fusarium Yellows
  • Xcc – Black Rot (Xanthomonas campestris)
  • DM – Downy Mildew
  • WR – White Rust

How to Use Resistance Codes When Choosing Varieties

  1. Match known problems in your garden.
    If you regularly see powdery mildew on squash, choose varieties with PM resistance.
  2. Stack resistances for resilience.
    A tomato with VFN + LB offers protection against both soilborne and airborne pathogens.
  3. Use them to reduce inputs.
    Resistant varieties need fewer sprays, fit regenerative practices, and stay productive under stress.
  4. Look for local matches.
    Pick resistances that target diseases common in your climate.

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.

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