Tomatoes originated in the South American Andes cultivated as early as 700 AD. They have become one of the central ingredients in many diets on all continents. It is now the most popular plant grown in home and commercial gardens across the world.
There are two basic types of Tomatoes with literally hundreds of hybrids and heirloom varieties.
- Determinate varieties grow as a small bush and set all of their fruit early in the year.
- Indeterminate varieties grow as a vine. They bloom and set fruit as they grow.
Growers living in hot summer temperatures should plan for the fact that indeterminate varieties will stop setting fruit when night temperatures reach approximately 85 degrees f. In warmer climates growers can plan for setting a fall crop by propagating cuttings from from the mature vines in late summer. Then plan for a new vigorous crop of tomatoes in the fall.
Unfortunately fungus, bacteria and virus love tomatoes as much as we do so care must be shown in selecting the tomato varieties we grow that are resistant to the strains of disease most prevalent in our areas. Otherwise our effort could be in vain.
Indeterminate varieties resistant codes can be found on the plant label or seed packet
Below are the Disease Resistance Codes and a brief description of the major diseases:
V Verticillium Wilt
F Fusarium Wilt
FF Fusarium, races 1 and 2
FFF Fusarium, races 1, 2, and 3
T Tobacco Mosaic Virus
St Stemphylium (Gray Leaf Spot)
TSWV Tomato Spotted Wilt Virus
What do each of these codes really mean?
- “V” means the plant is resistant to the fungi that cause verticillium wilt, Verticillium albo-atrum and Verticillium dahliae. The fungi work their way up through the plant’s roots, clogging water-conducting tissue in the stem. They spreads a toxin that wilts leaves and prevents water from reaching branches and leaves, starving the plant. Yellow spots appear on lower leaves, followed by brown veins. Leaves then turn brown and fall off. Infection pattern often resembles a V-shape.
- "F," "FF," or “FFF” means the plant is resistant to Fusarium oxysporum fungi that cause fusarium wilt. First signs are yellowing and wilting on one side of the plant – a leaf, single shoot, branch, or several branches. Yellowing and wilting move up the plant as the fungus spreads, clogging water-conducting tissue in the stem and affectively starving the plant. Left unchecked, fusarium wilt can kill tomato plants well before harvest time. Unfortunately, some fusarium fungi have overcome the initial - “F” resistance attributes in designated tomatoes. Today, newer cultivars have been bred to be resistant to secondary fusarium strains – hence the “FF” and “FFF” designations.
- "N" means the plant is resistant to nematodes, parasitic round worms that often lie dormant in the soil. Nematodes can produce root galls on the plant up to an inch wide. Affected plants are weak, stunted, do not respond to fertilizer, and tend to wilt.
- "A"means the plant is resistant to the Alternaria alternata fungus that causes Alternaria stem canker. Brown or black cankers attack tomato stems, leaves, and fruit, often accompanied by streaks. Left unchecked, cankers can spread across the entire plant and kill it before harvest.
- "T" means that the plant is resistant to the Tobacco Mosaic Virus (TMV), which causes mottling and yellowing in tomato leaves, reduced tomato size and yield, and brown fruit.
"St" means the plant is resistant to Stemphylium or gray leaf spot, caused by the Stemphylium solani fungus. Affected plants develop brown to black spots, which progressively get bigger, turn gray, and drop out – leaving holes.
- "TSWV" means plants are resistant to the Tomato Spotted Wilt Virus. Symptoms vary from plant to plant, but can include yellow and brown rings on stems, brown streaks on p stems, dead leaf spots and tips, and severely stunted growth. Fruit may be discolored at maturity.
A brief video on shopping for tomato plants: