AMSEED American Seed Intelligence Platform
AMSeed · American Seed Intelligence Platform https://amseed.com/diseases/root-knot-nematode
pest

Root-Knot Nematode

Issue type
pest
Seedborne
No
Resistance code
N
Affects
Tomato, Cucumber, Watermelon

Symptoms

Stunted, wilt-prone plants that fail to respond to water and fertilizer; roots carry the diagnostic galls, swollen knots where juveniles feed. Damage concentrates in sandy soils and warm climates.

Management

The Mi gene (code N) makes resistant tomato hybrids the standard defense, with the caveat that Mi-mediated resistance weakens at sustained soil temperatures above ~82°F. Rotation to non-hosts like grasses and marigold cover-cropping reduce populations; heirlooms in infested sandy ground generally need grafting or containers.

Varieties with documented resistance

VarietyLevelCodeBasisDaysBreeding
Better Boy resistant N Breeder declared 70-75 F1 hybrid
Celebrity resistant N Breeder declared 70-72 F1 hybrid
Big Beef resistant N Breeder declared 70-73 F1 hybrid
Mountain Merit resistant N Independently observed 73-77 F1 hybrid
Amelia resistant N Independently observed 75-80 F1 hybrid
Lemon Boy resistant N Breeder declared 72-75 F1 hybrid
Mountain Fresh Plus resistant N Breeder declared 75-78 F1 hybrid
Damsel resistant N Breeder declared 70-75 F1 hybrid
Viva Italia resistant N Breeder declared 72-80 F1 hybrid
Super Marzano resistant N Breeder declared 70-80 F1 hybrid
Sweet Chelsea resistant N Breeder declared 65-70 F1 hybrid
Bush Early Girl resistant N Breeder declared 54-63 F1 hybrid
Better Bush resistant N Breeder declared 68-72 F1 hybrid
Bush Goliath resistant N Breeder declared 65-70 F1 hybrid
Beefmaster resistant N Breeder declared 80-85 F1 hybrid
SuperSteak resistant N Breeder declared 80-85 F1 hybrid
Park's Whopper resistant N Breeder declared 65-70 F1 hybrid
Champion resistant N Breeder declared 62-70 F1 hybrid
Crista resistant N Breeder declared 72-78 F1 hybrid
Red Snapper resistant N Breeder declared 70-75 F1 hybrid

This is the page where the difference matters most, because it is where a variety gets chosen for its resistance. Breeder declared means the claim comes from whoever breeds or sells the seed, which for most resistance genes is the only evidence that exists. Independently observed means an institution with no stake in the sale grew the plant and reported what happened.

Sources & References

Evidence: 2 sources, all independent references.

  1. Vegetable MD Online · Cornell University, Plant Pathology, University or Government
  2. Tomato Production and Cultivar Guides · University of Florida IFAS Extension, University or Government