Modern botanical science has given us hundreds of hybrid tomato varieties. Some are bred to grow faster or taste better, but the best quality of hybrid tomatoes is their disease resistance.
Modern botanical science has given us hundreds of hybrid tomato varieties. Some are bred to grow faster or taste better, but the best quality of hybrid tomatoes
is their disease resistance.
Many tomatoes are bred to resist specific diseases, which can really help a gardener grow healthy plants. When you see a tomato plant tag with a combination of capital letters like VFN following its name, those letters stand for the disease strains that the plant is resistant to.
Here's what those letters mean:
- “V” means the plant is resistant to the fungi that cause verticillium wilt, Verticillium albo-atrum and Verticillium dahliae. These fungi invade the plant through its roots, harming tissue in the stem that allows water transfer. They spread a toxin that 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.
- "F," "FF," or “FFF” means the plant is resistant to fusarium wilt, caused by the fungi, Fusarium oxysporum. The first signs of infection are yellowing and wilting on one side of the plant–a leaf, single shoot, branch, or several branches. Yellowing and wilting gradually move up the plant as the fungus spreads, clogging water-conducting tissue in the stem and and starving the plant. Left untreated, fusarium wilt can kill tomato plants before harvest time. Unfortunately, some fusarium fungi have overcome the initial “F” resistance attributes in disease-resistant tomatoes. Today, newer hybrid tomato cultivars have been bred to be resistant to these stronger fusarium strains, hence the “FF” and “FFF” designations.
- "N" means the plant is resistant to nematodes, parasitic worms that often lie dormant in the soil. Nematodes can hurt the plant from its roots. Affected plants are weak, stunted, do not respond to fertilizer and often wilt.
- "A" means the plant is resistant to the Alternaria alternata fungus that causes Alternaria stem canker. These cankers appear as wet, open lesions on the plant. Brown or black cankers attack tomato stems, leaves and fruit, often accompanied by streaks. Left untreated, cankers can consume the entire plant and kill it before harvest.
- "T" means that the plant is resistant to 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, also known as 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 slightly from plant to plant, but generally include yellow and brown rings on stems; brown streaks on stems; dead leaf tips; and severely stunted plant growth. Fruit may also be discolored when it matures.
Planting disease-resistant tomatoes isn't a requirement, but it can make things easier. Although the diseases can be treated when caught, resistant tomatoes will never have the problems in the first place.