Sustainable Practices for Vegetable Production in the South
Dr. Mary Peet, NCSU
Home

Tomato

BOTANY

Plant Characteristics

Tomatoes are short-lived perennials cropped as annuals. Although killed by frost outdoors, in greenhouses, plants can be cropped for 24 months or longer.

Growth habits: determinate vs. indeterminate. The primary shoot of a young tomato plant produces 5 to 10 leaves, then produces a flower cluster. Each flower cluster is referred to as a 'hand'. In indeterminate cultivars, the shoot continues to grow upward and flower clusters appear to develop to the side of a main shoot or main stem. In greenhouses, main stems are sometimes allowed to grow indefinitely and can reach 10 to 20 feet in length. In order to make harvest easier, older leaves are pic ked off and the bare stems lowered to the ground. Only the youngest 6 to 7 feet of plant growth, which includes the developing fruit clusters, are trained upright. In this training system, that vegetative side shoots or suckers which form in leaf axils are removed.

Although indeterminate plants appear to have a single main stem, this is actually not the case. The growth of the primary shoot ends with the formation of the first flower. Upward growth continues because the last leaf initiated before the flower cluste r (which actually grows to occupy a position above the cluster) produces a side shoot. This side shoot produces three more leaves before it terminates in a flower cluster. The process of initiating new growth from a side shoot of the last leaf initiated before the flower cluster continues indefinitely, giving the appearance of a mainstem with a flower cluster between every three leaves.

In determinate cultivars, the process differs in that the side shoot above the first flower cluster produces 0 to 2 leaves and a flower cluster but no further vegetative shoots. This ends the upward growth of the plant, making the apparent main stem much shorter. Many side shoots arise from the primary shoot, giving the plant a bushy appearance, but each eventually terminates in a flower cluster. The simultaneous growth of many flower clusters promotes earliness and concentrates fruit maturity compared to indeterminates. Shoots of semideterminate plants produce several flower clusters to the side of an apparent main stem, like indeterminates, but eventually the shoot terminates in a flower cluster, as in determinate plants.

Most commercially grown processing and fresh market tomatoes have a determinate growth habit, because their shorter stature makes them easier to stake and the concentrated maturity reduces the harvest period, which generally reduces labor costs. Indeterm inates are used in greenhouse production and by home gardeners because of the longer, less concentrated harvest period.

Fruit Characteristics. The tomato fruit is a classified botanically as berry. Size varies from small cherry types with only two divisions of the ovary (locules) to large multi-locular beefsteak types.

Two-locules wild types: Examples are cherry tomatoes and processing (plum or pear) types. Cherry tomatoes are small and round and grown only for fresh market. Processing types are usually somewhat larger and can be pear, plum or 'square-round' in shape. Although most processing tomatoes are canned or processed into sauces and condiments, small percentages are also sold fresh or as 'sun-dried' tomatoes. Four to six locules: Examples are most commercial cultivars for fresh market. More than six locules: Examples are the large 'beefsteak' types. Although the eating quality is very good, beefsteak tomatoes are now grown mainly in greenhouses or by home gardeners because they do not ship well and are more likely to crack and to be irregularly shaped.

Color. Fruit can be yellow, orange, pink, red, or even white. The red color comes from the pigment lycopene while the orange and yellow colors come from betacarotene pigments. Yellow and orange tomatoes are equal or higher in nutrition to red tom atoes because lycopene has no particular nutritional value while carotenoids are a source of vitamin A. Pink tomatoes have the same interior color as red tomatoes but have a transparent rather than yellow skin.

Shape. Fresh market tomatoes range from round to oblate (flat-round) while processing tomatoes are more elongated (oblong) or pear-shaped. Breeders of processing tomatoes have developed oblong types with squarer shoulders (called square-rounds) t o resist crushing. Old tomato cultivars are of many shapes and sizes, including ridged.

Composition.

Fresh Market: Most of the fruit fresh weight is water, with solids constituting only 5 percent. These solids consist of water insoluble substances such as cell walls, and soluble components such as sugars and acids. The amount of sugar present ( generally about half of the solids) and the amount of acids present (generally about one-eighth of the solids) and their ratio determine flavor. High sugars and high acid are the best combination for good flavor. Low sugar/high acid tomatoes are tart; high sugar/low acid tomatoes are bland; and low sugar/low acid tomatoes are tasteless. Processing: Processing tomatoes are canned or cooked down into sauces and tomato paste. They have thicker walls and are firmer than most fresh market cultivars so they will hold their shape when cooked. It costs money to remove the water and to dispose of wastewater so processors prefer cultivars with higher soluble solids than in fresh market tomatoes. A high ratio of water insoluble solids to total solids is also important in ketchup and other consistency products. After all, who wants runny ketchup or tomato paste?

Climatic Requirements

Although we think of tomatoes as an adaptable crop, they are actually quite sensitive to low light and adverse temperatures. Tomatoes need at least 6 hours of direct sunlight to flower. Slender, non-fruiting tomato vines are a common complaint of home gardeners and are usually traceable to shading. Many homeowner and grower complaints can also be attributed to high or low temperatures. Although tomatoes grow well over a wide range of temperatures (65 to 85 degrees F), fruit set is very sensitive to high and low temperatures. Above 90 degrees F day or 70 degrees F night temperatures and below 50 to 55 degrees F, flowers may produce oddly-shaped (rough) fruit or flowers may fall off without setting fruit at all. Malformed fruit are sometimes said to be 'catfaced' or to have open locules. These malformations are the result of incomplete separation of cells during the early stages of flower and fruit development. Adverse effects seem to be worst when both day and night temperatures are high or when both are low. Proper coloring of the fruit is also temperature dependent. Lycopene and carotenes are not synthesized above 85 degrees F and lycopene is not synthesized below 50 degrees F, precluding normal color development in ripening fruit.

Location of Production

By acres harvested in 1992 in the United States, the top states for tomato production were California, Florida, Ohio, Indiana, and Michigan. With the exception of greenhouse tomatoes, the entire U.S. crop comes from Florida or Mexico from November through May. Twenty percent of the fresh tomatoes consumed in the U.S. are imported. Of the total acres of both processing and fresh market tomatoes harvested in the United States, 11.2 percent are in the Southern Region. The top five states in 1992 were Florida, 63,423 acres; Tennessee, 4,300; Virginia, 3,495; Texas, 3,260; and South Carolina, 3,043. Consumption of tomatoes exceeds all vegetables except potatoes.

Nutrition

One medium fresh tomato provides 47 percent RDA of Vitamin C, 22 percent RDA Vitamin A and 25 calories (135g). Although not high in nutrients compared to other vegetables, the tomato ranks number one in contribution to diet in the United States because of the large quantities consumed.