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Farming

Varieties

How do we choose the perfect varieties?

Choosing which tomato variety/varieties to plant is probably one of the most critical decisions commercial producers make each year. This article discusses the various factors that can affect this decision, starting with a simple discussion about the two basic types of tomato varieties available in the marketplace, and a brief discussion about grafted plants.

Open-Pollinated Varieties
Tomato plants are predominately self-pollinated, so open-pollinated (OP) seed varieties are inbred lines that are very stable from one generation to the next. Any observed variation in an OP variety is most likely due to chance outcrossing to another variety, the frequency of which is very low if basic quality control methods (e.g., isolation) are used in seed production. It is possible, but even less likely, that a mutation in the last generation impacted an important trait.

What we today call “heirloom” varieties were, by definition, OP varieties developed over 50 years ago. These heirloom varieties were usually selected over dozens of generations by families or communities who saved seeds of their favorites types each year. Exceptional flavor was often a primary selection criterion—which is why most of our standards for flavor are based on old heirloom types, such as Cherokee Purple, Pink Brandywine, and Kellogg’s Breakfast. This reputation and a fondness for the history of these types often lead to a market premium at farm stands and farmers markets. Some popular heirloom tomato varieties produce fruit of virtually every combination of color, size, and shape. Heirloom varieties also vary in earliness, fruit yield, fruit quality, and plant health, but the two weaknesses common to many heirloom tomato varieties are low/medium fruit yield and poor fruit quality (e.g., cracking, splitting, and cat-facing).

Several more recently developed OP varieties are selected for good flavor, but also they may have improved fruit yield/quality and plant health. There are probably a dozen or more independent tomato breeders developing these types today, many of whom sell seed from their websites directly to consumers. Some of these have now been planted by hundreds of growers over a period of a decade or more, such as Green Zebra, Berkeley Tie Dye, and Blush—and perhaps these will become the next-generation heirlooms.

 

F1 Hybrids
An F1 hybrid results from crossing two inbred (OP) lines. All the processing types—and the vast majority of commercial fresh market tomatoes—are produced using F1 hybrid seed/plants. In tomatoes, as in all other hybrid crops, there is often “hybrid vigor,” or heterosis, in F1 hybrids that results in a significant increase in crop yield. In tomatoes, there is often heterosis for flavor too. Heterosis is defined as an F1 hybrid that performs better than either of its parents. F1 hybrids also allow an efficient method of combining traits from unrelated and complementary parents. For example, disease resistance is generally controlled by dominant alleles so that one parent with resistance to diseases A, B, and C, which is crossed to a second parent resistant to diseases D, E, and F, results in an F1 hybrid resistant to all six diseases.

A common critique for F1 hybrid tomato seed has been lack of flavor. Indeed, commercial tomato breeders have historically focused on plant health, fruit quality, and “transportation-friendly” types—with flavor taking a backseat in the breeding process (note exceptions, such as Sungold F1). Today, consumers demand better flavor, and most commercial tomato hybrid breeding programs use heirloom types as a key germplasm source and are selecting for a combination of flavor, fruit yield/quality, and plant health/disease resistance. The best newer hybrids rival heirlooms for flavor and have a significant increase in yield of marketable fruit and improved shelf life.

Grafted Plants
Tomato grafting has long been used for high-value greenhouse plants in Europe and is becoming more popular in the US. The rootstock generally provides resistance to root diseases and nematodes, and increased root vigor may also provide for increased fruit yield. The scion, or upper part of the grafted plant, is selected for fruit type, flavor, and quality. Grafted plants, mostly with heirloom scions, are available from several retailers. For those who want to do their own grafting, seed of various rootstocks is available from several seed companies, and many YouTube videos show various grafting methods (see references).

Here’s some general advice on deciding what to plant:
1) Plant what you can sell. Local and regional markets can vary widely in the relative market size and price premium for organic vs. conventional, and for popular heirlooms vs. non-heirloom OP and hybrid types. There also may be regional preferences for fruit size, shape, and color, and for fresh market vs. canning types. Specialty types (unconventional colors, stripes, shapes, and sizes) are hot in some urban markets and a tough sell in markets with a strong preference for red beefsteak-type tomatoes. If you’re expanding your market to include local restaurants, you may find them eager to use something “new and exciting,” with a different taste profile, color, and/or shape. Specialty types might also help differentiate your offering from other tomato sellers at farmers markets.

2) Plant a variety that is ideally adapted to your growing conditions or production system. If your production system depends on two crops a year and minimal staking, early determinate types probably make sense. Length of growing season, especially with open-field production, may limit your choices to early and mid-season types. Good plant health is critical for optimal fruit yield, so know what disease problems are prevalent in your area and look for varieties with tolerance or resistance. If you’re producing in a hoop house or greenhouse, an indeterminate type with resistance to ToMV, leaf mold, and powdery mildew might be ideal. Open-field production in an area prone to late blight would suggest a variety resistant to this pest. If you’re an organic grower, check with your organic certifier if you can’t find the desired variety as organic seed and you want to exercise the seed exemption (7 CFR §205-204).

3) For most market producers, yield of marketable fruit per unit area (open field or protected culture) will be an economic driver. Unfortunately, there is very little regionally relevant performance data comparing varieties. A new startup company called SeedLinked 1 enlists tomato growers to test and compare locally adapted varieties. The seed is supplied by regional seed companies. Growers collect performance data and observations on the varieties, and SeedLinked analyzes the matrix of data generated and shares data summaries with the participating growers. It allows growers to learn which varieties are and are not working in their region under similar crop management (e.g., open field vs. protected culture). Another method of getting relevant comparison information is to do it on your own farm by introducing at least a few new varieties each year to compare with your current favorites.

  1. https://www.seedlinked.com/recommended_varieties/[]
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