Farmer's Weekly (South Africa)
The development of the modern tomato
With tomatoes a major crop worldwide, it should come as no surprise that there are so many varieties, says Bill Kerr.
MANY TOMATOES GROWN IN SOUTH AFRICA ARE RELATIVELY TASTELESS AND WATERY
Tomatoes originated in the Andes mountains, mainly in Ecuador and Peru. There are many species of wild tomatoes, but they look nothing like the varieties we use today.
As is often the case, scientists change the Latin names of plants from time to time, which causes confusion. A case in point is the common market tomato Lycopersicum esculentum, which was changed to Solanum lycopersicum. Bear this in mind when reading old literature on tomatoes.
CHERRY TOMATOES
Tomatoes arrived rather late to our tables compared with most other vegetables; they have been in use for only a few hundred years.
They were originally regarded with suspicion, as so many members of the Solanum genus are poisonous. The French at one time called them ‘love apples’, believing them to have aphrodisiac properties.
Tomatoes were also used initially as ornamental plants.
Modern cherry tomatoes have many beneficial genes conferred by the wild species S. pimpinellifolium. This species is very hardy and resistant to stress, and many selections have good salt tolerance.
Some selections are also resistant to late blight, Stemphylium and bacterial speck, and these genes have been transferred to modern tomatoes.
USED IN CROSSES
Cherry tomatoes often appear in gardens, the seeds having been transported there by birds with a little ‘organic fertiliser’. They usually grow well.
A species that’s not eaten, but used in crosses to make rootstock for grafting, is S. habrochaites. It’s exceptionally vigorous, has a distinct aroma, and its leaves look more like those of a mint plant. The fruit is small and turns green to light orange, while the flowers are bright yellow and highly attractive to carpenter bees. The vigour and health of the plant is transferred from the rootstock, giving higher yields.
South African consumers prefer red tomatoes, whereas the Japanese, for example, like pink varieties. Yellow has moderate acceptance in some countries. Other colours used to a limited extent are black, brown, orange, green and blue. Different colours provide different antioxidants.
Over the years, mutants have cropped up, some of which have been widely used in modern varieties. Originally, tomatoes had green shoulders, which would on occasion fade during ripening, but an intense green shoulder would cause unattractive yellow blotching in the green area at ripening. Then a mutation appeared that gave the fruit a uniform colour; called the ug gene, it was immediately accepted and is now the norm.
The ug gene has one big disadvantage: it results in less tasty fruit.
WATERY TOMATOES
Another mutant gene that cropped up was the rin (ripening inhibitor) gene. This proved popular as it slows down the ripening process and thereby extends the shelf life of the fruit.
The rin gene parents are an orangey colour, and when crossed with a red variety, produce a hybrid that’s a lighter colour than the red parent. Many tomatoes grown in South Africa are of this cross and are relatively tasteless and watery; they also have a lower lycopene content.
Consumers in many countries will not accept these; Germans, for example, refer to them as ‘water balls’ and reject them.
Bill Kerr is a vegetable specialist and a breeder of a range of vegetables. Email him at farmersweekly@caxton.co.za. Subject line: Vegetable production.