Tomato growers often notice a series of letters following the names of tomato varieties on plant labels or seed packets. These codes indicate genetic resistance to certain diseases or pests that can affect tomato crops. For example, “Early Girl—V,F,N,TMV” and “Chef’s Choice Pink—F,N,A,TMV” display such codes.
According to the University of California Agriculture and Natural Resources (UC ANR), these resistance markers do not mean complete immunity but can help plants tolerate specific pathogens. This tolerance allows many resistant varieties to reach maturity and produce fruit even when exposed to disease pressures. Most hybrid tomatoes carry one or more resistance codes, while heirloom varieties rarely have them. Newer varieties continue to be developed with broader resistance.
Some common disease and pest resistance codes include:
– A: Alternaria stem canker, affecting mostly coastal tomatoes.
– F/FF/FFF: Fusarium wilt strains 1, 2, and 3.
– V: Verticillium wilt.
– LB: Late blight.
– EB: Early blight.
– T/TMV: Tobacco mosaic virus.
– ToMV: Tomato mosaic virus.
– TSWV: Tomato spotted wilt virus.
– N: Nematodes.
These diseases and pests are significant threats because most have no cure once a plant is infected. Where treatments exist, they are often not fully effective. Planting resistant varieties remains the most reliable option for many gardeners.
Each code refers to a specific pathogen or pest. For instance, nematodes are microscopic roundworms that attack plant roots, leading to swelling on roots and stunted growth above ground. Fungal diseases like fusarium and verticillium wilts block water flow in plants and cause yellowing leaves. Viral infections such as tobacco mosaic virus lead to leaf discoloration and reduced fruit quality.
If symptoms of these issues appear in a garden, identifying the problem can help plan for future planting of resistant varieties. UC ANR recommends consulting resources like the University of California Integrated Pest Management website for more details about disease spread and symptom identification (https://ipm.ucanr.edu/home-and-landscape/tomato/index.html).
UC Agriculture and Natural Resources enhances lives across California by sharing science-based practices through research and outreach initiatives (https://ucanr.edu/). The organization maintains nine Research and Extension Centers as living laboratories throughout diverse ecosystems in California (https://ucanr.edu/) and operates offices in all 58 counties (https://ucanr.edu/). It is affiliated with the University of California system (https://ucanr.edu/) and applies university expertise to support local communities (https://ucanr.edu/). Glenda Humiston serves as vice president of UC Agriculture and Natural Resources (https://ucanr.edu/).
For over a century, UC ANR has provided resources in nutrition, food networks, youth education, farming practices, environmental conservation, wildfire protection, and more through collaborations statewide (https://ucanr.edu/).
For further assistance on tomato diseases or selecting resistant varieties suitable for Contra Costa County conditions, local gardeners can contact the Help Desk of UC Master Gardeners of Contra Costa County.