When you are going to buy tomato seeds or plants, you may find some special letters alphabet in the seed packet or plant level. These are the tomato disease resistance codes for that specific variety.
You may also find these tomato disease-resistant codes when searching for different garden blogs or e-commerce sites.
If you are a beginner gardener, you may often fall in confusion about identifying which code indicates which disease.
So, I suggest you get some primary knowledge about the disease resistance codes of tomatoes before buying tomato seeds or plants.
Tomato Diseases Resistance Codes
These codes are very useful information for choosing which tomato varieties to buy for your growing region. Sometimes you may find various codes for the same disease. Besides, different seed companies present the same disease code in different ways. So, it’s a little bit confusing.
These disease resistance codes are especially gardening lingo which represents the plant characteristics.
For example-
If you find a tomato seed packet or a plant label with a resistant code like VFFNSt after its name, those meats it resistant to Verticillium wilt, Fusarium Wilt (Races 1 and 2), Root-knot Nematodes, Stemphylium Grey Spot Leaf.
Typically, every single letter stands for a specific disease, but sometimes a group of letters stands for a particular disease or pest.
Besides you may also notice HR or IR codes which stand for:
- HR= High Resistance
- IR= Intermediate Resistance
Here I decipher and introduce the most common disease resistance codes for tomatoes.
A – Anthracnose
Scientific Name: Colletotrichum lagenarium
Type: Fungus
Causes and Symptoms:
- This disease mainly affects tomato fruits but also attack leaves, stems, and roots.
- Lesions appear on leaves and gradually create a yellowish circular spot.
- Black sunken water-soaked round spots appear on tomatoes.
- The disease flourishes in high moisture and humid weather condition when the temperature remains between 75-82° F.
Most Susceptible Regions:
Southern, mid-Atlantic, and mid-Western parts of the United States.
A / Aal / AS/ ASC – Alternaria Stem Canker
Scientific Name: Alternaria alternata f.sp. lycopersici
Type: Fungus
Causes and Symptoms:
- Primarily small brown or dark spots appear on stems.
- Gradually the cankers grow bigger to girdle the whole stem and kill the plants.
- The diseases can attack the base of the plant or other parts of the tomato plants.
- It can also attack tomato leaves and fruits.
Most Susceptible Regions:
All over the United States.
BS or (Pst/Pst: 0) – Bacterial Speck (Races 0)
Scientific Name: Pseudomonas syringae
Type: Bacterium
Causes and Symptoms:
- Brown spots are surrounded by yellow rings on the leaves.
- Leaf curling.
- Fruits may also affect severe cases.
- The disease spread out by seeds, human movement, garden tools, wind, and water.
Most Susceptible Regions:
The disease is favorable when the temperatures are 63-75° F with high moisture and humid weather condition all over the United States.
BW – Bacterial Wilt
Scientific Name: Erwinia tracheiphila
Type: Bacterium
Causes and Symptoms:
- Stunt the growth of the tomato plants.
- At the primary stage, particular leaves are wilting and drying.
- Suddenly the entire stems become wilting and drying out.
- Wilting occurs during the mid-day and recovers at night.
- After that, wilting spreads out all through the vines and ultimately kills the plants.
- The disease spreads through cucumber beetles.
Most Susceptible Regions:
Tropical and sub-tropical regions with high humidity and temperatures.
CRR – Corky Root Rot
Scientific Name: Pyrenochaeta lycopersici
Type: Fungus
Causes and Symptoms:
- Early planting when the temperature is down below 60° to 68°F is the main cause behind the diseases.
- Cork shape brown lesions develop in bands with lengthwise cracking on the larger stems.
- The tips of the damaged roots are pinched off.
- Plants grow up slowly.
- Reduces yields but doesn’t kill the plants.
Most Susceptible Regions:
All over the United States mostly in northern or cooler parts.
EB/AB – Early Blight (Alternaria Blight)
Scientific Name: Alternaria solani
Type: Fungus
- Causes and Symptoms:
- Small dark spots appear on the lower leaves.
- Circular brown spots can grow up on plant leaves.
- Larger spots create concentric rings like brown to yellow.
- Finally, the leaves drop off.
- Brown, sunken spots girdle the plant stems just above the soil line.
- Concentric leathery spots may appear on Fruits and finally drop off.
- Sunscald or fruit crack may also occur.
Most Susceptible Regions:
Warm regions of the United States, especially southern parts.
F/FF/FFF or (Fol: 1, 2, 3) – Fusarium Wilt (Races 1, 2 and 3)
Scientific Name: Fusarium oxysporum, Fusarium oxysporum f. sp. lycopersici
Type: Fungus
Causes and Symptoms:
- Diseases start from the roots and climb up to the stems.
- Lower leaves turn yellowing and browning.
- Plants stop growing and wilting.
- The plant produces little or no fruits.
- Finally, the entire plant becomes dry.
Most Susceptible Regions:
F- Warm regions all over the United States.
FF – Arkansas, Florida, New Jersey, and Ohio in the United States.
FFF- California, Florida, North Carolina, and South Carolina in the United States.
FOR – Fusarium Crown and Root Rot
Scientific Name: Fusarium oxysporum f. sp. radicis–lycopersici
Type: Fungus
Causes and Symptoms:
- Attacks mature plants.
- Gradually reduces fruit production and growth.
- Stunting, wilting, dry rot of the crowns.
- Yellowing the edges of the older leaves.
- Dry reddish-brown lesions may develop on stems above the soil line and the cortex of the taproot.
- Old plants may die.
Most Susceptible Regions:
All over California, especially greenhouses and cool soil temperatures.
LB – Late Blight
Scientific Name: Phytophthora infestans
Type: Oomycete, Water Mold, Fungus
Causes and Symptoms:
- Dark brown blotches on leaves turned into dry brown foliage.
- The lesions may also appear on tomato plant stems and fruits.
- The entire field may turn brown and wilted and create significant yield loss in a few days after the first lesions appeared.
Most Susceptible Regions:
The disease performs better when the temperatures are 60-70° F with high moisture and humid weather condition all over the United States.
LM or (Ff: A-E) – Leaf Mold (Races A, B, C, D, and E)
Scientific Name: Passalora fulva, Cladosporium fulvum, Fulvia fulva,
Type: Fungus
Causes and Symptoms:
- Greenish-yellow spots appear on the front sides of the leaves and turn brown.
- Leaves start wilting and dry off.
- Dark spots appear on blossoms and finally fall off.
- Diseases are spread by garden tools, human movement, wind, and water.
Most Susceptible Regions:
The disease prefers when the temperatures are 71-75° F with high moisture and humid weather condition all over the United States.
N or (Ma/Mi/Mj) – Root-Knot Nematode
Scientific Name: Meloidogyne spp., Meloidogyne arenaria, M. incognita, M. javanica
Type: Parasites
Causes and Symptoms:
- Leaves turn yellow and wilting and stop growing.
- Roots become galled and decayed.
- Performs better in warm soil with high moisture while temperatures rise up to 85 – 95° F.
Most Susceptible Regions:
Most warm regions with high soil moisture in the United States.
PM or (On) – Powdery Mildew
Scientific Name: Oidium neolycopersici, Oidium lycopersicum, Leveillula taurica, Oidium lucopersici
Type: Fungus
Causes and Symptoms:
- White powdery patches appear underside of the lower leaves.
- The upper side of the leaves appears yellow to brownish spots and shrinking.
Most Susceptible Regions:
Tropic and sub-tropic regions, particularly North, South, and Central America.
St or GLS – Stemphylium Gray Spot Leaf (Gray Leaf Spot)
Scientific Name: Stemphylium solani, S. lycopersici, S. floridanum, and S. botryosum
Type: Fungus
Causes and Symptoms:
- Brown to black specks appears on tomato leaves.
- Small round gray spots slowly develop on plant leaves surrounded by the yellow area.
- Leaves turn yellow to brown and drop off.
- Finally, the plants stop growing.
Most Susceptible Regions:
Warm regions, most commonly Southeastern parts of the United States.
T or TMV – Tobacco Mosaic Virus
Disease Name: Scientific Name: Tobacco mosaic virus, positive-sense single-stranded RNA virus (Tobamovirus)
Type: Virus – Potyvirus
Causes and Symptoms:
- It damages flowers, leaves, and tomatoes rather than kills them.
- Appear irregular yellow-green, light-green, or dark-green spots on leaves.
- Plants stop growing and produce fewer yields.
- Sunken brown ring spots may appear on tomatoes.
Most Susceptible Regions:
Found worldwide and throughout the United States. The disease may spread out through infected plant debris, using garden tools after using Tobacco products, or while smoking in the garden.
ToMV or (ToMV:0-2) – Tomato Mosaic Virus (Races 0, 1, and 2)
Scientific Name: Tobamovirus
Type: Virus
Causes and Symptoms:
- Leaves appear dark green to yellow spots, small in size, and curled.
- Yellow ring spots appear on tomato fruits and ripen unevenly.
Most Susceptible Regions:
Warm regions.
TSWV or SWV – Tomato spotted wilt virus
Scientific Name: Tomato spotted wilt virus (genus Tospovirus; family Bunyaviridae)
Type: Virus – Tospovirus
Causes and Symptoms:
Upper leaves change their color from yellow to brown ring spots
- Plants stop growing, and dark streaking appears on stems.
- Produces irregular shapes of fruits.
- Plants become wilted and finally die off.
- The virus may transmit by Thrips.
Most Susceptible Regions:
Found throughout the United States.
TYLCV – Tomato Yellow Leaf Curl Virus
Scientific Name: Begomovirusa (Tomato yellow leaf curl virus)
Type: Virus
Causes and Symptoms:
- Reducing leaf size, stunting, and yellowing.
- Leaves curling upwards.
- Infected plants don’t develop flowers.
- Fruits fall off earlier.
Most Susceptible Regions:
California and Florida.
V / Va / Vd – Verticillium Wilt (Races Va: 1 or Vd: 1)
Scientific Name: Verticillium dahlia, Verticillium albo–atrum
Type: Fungus
Causes and Symptoms:
- Soil-borne/seed-borne tomato disease.
- Spread through gardening tools, wind, and water.
- Wilting, yellowing of leaves, defoliation.
Most Susceptible Regions:
Most regions of the United States.
