However, their seeming diversity is only skin-deep: heirlooms are actually feeble and inbred—the defective product of breeding experiments that began hundreds of years ago, and exploded thanks to enthusiastic backyard gardeners. ‘The irony of all this,’ says Steven Tanksley, ‘is all that diversity of heirlooms can be accounted for by a handful of genes. There’re probably no more than 10 mutant genes that create the diversity of heirlooms you see.’
To discover those genes, Esther van der Knaap, took a gene from one heirloom tomato and inserted it into a wild relative. She observed that, as a result, the tiny fruits became shaped like pears.
Wild plants must continuously evolve to fend off such infections, points out Roger Chetelat. But in their quest for size, shape and flavour, humans have inadvertently eliminated defensive genes. As a result, most possess only a single disease-resistant gene. He elaborates that heirlooms’ table may have less to do with their genes than with the productivity of the plant and the growing environment.
In 1996 a tomato breeder and former Tanksley student named Doug Heath began a favourite project. After 12 years of traditional breeding with the help of molecular markers, he created a new multi-coloured tomato less prone to cracking and also endowed with 12 disease-resistant genes. The original heirloom plant, Heath explains, had defective flowers, which is one reason why it produced only two fruits compared with the 30 he gets from his new variety. He claims he is also able to maintain a comparable flavour and sugar profile even on productive plants.
Questions
1. The transplanting of certain genes into tomatoes can change their shape.
2. The flavour of the heirloom tomato is largely dependent on actual yield and cultivation.
3. A new type of tomato can be produced that is stronger than the original heirloom tomato yet equally sweet and flavoursome.
4. The wide variety of heirloom tomatoes is due to only a small number of genes.